Android for Python Users

An unofficial Buildozer Users' Guide

2023-11-13 This repository is archived.

Revised 2023-10-17

Table of Contents

Introduction
Confidence and Competence
What is Different about Android?
- Posix
- Android Lifecycle
- Wheels
- Meta-information
- App Security
Android Storage
- Private Storage
- Shared Storage
- Sharing a file between apps
Concurrency
- Threads
- Subprocess
- Async
Android Service
- Specifying a Service
- Service Lifetime
- Service Notifications
- p4a Service Implementation
App Permissions
- Manifest Permissions
- User Permissions
Buildozer and p4a
- Install
- Try Hello World
- Changing buildozer.spec
- What should I change?
- If Buildozer fails to compile
- Some buildozer.spec options
- Most Common Issues
- Non-deterministic Behavior
Debugging
- Install App on Android
- Get an Error Message
- I Included Android Permissions, but....
- Slow App Start
Android Hardware
- Camera
- Keyboard
- Back Button and Gesture
Android Packages
- The Android package
  - BroadcastReceiver
- Plyer
- Pyjnius
Kivy Related Topics
- disable_multitouch
- Layout
- Kivy Filechooser
- KivyMD
- Kivy Lifecycle
- Kivy Garden
Creating a Recipe
- Why a Recipe
- Porting Overview
- P4A Recipe API
- Porting Build Instructions
- Recipe Support
Resources
- Read the Fine Manual
- Android for Python
- KivAds and KivMob
- Android Notifications
- Android Billing
- Other Resources
Release Builds
- Setup signing
- Build the release
Appendix A : Using adb
Appendix B : Using an emulator
Appendix C : Locally modifying a recipe
Appendix D : Debugging on WSL
Appendix E : Copying from private storage
Appendix F : Install Bundletool
Appendix G : Modifying p4a
Appendix H : Cryptic Error Messages
- No module named 'msvcrt'
- Aidl not found
- Sdkmanager is not installed
- 64-bit instead of 32-bit
- EM_X86_64 instead of EM_AARCH64
- No module named '_Socket'
- weakly-referenced object
- OpenCV requires Android SDK Tools
- No such file or directory: 'ffmpeg'
- Unsupported class file major version 62
- Permission denied: '/storage/emulated/0/...'
- ModuleNotFoundError: No module named 'PIL'
- Requested API target 27 is not available
- BUILD FAILURE: No main.py(o)
- /usr/bin/gzip: 1: ELF : not found
- SSL: CERTIFICATE_VERIFY_FAILED
- gradlew failed!
- android:exported
- null pointer dereference
- No module named 'android'
- Hunk #1 FAILED
- Kivy is too old
- C compiler cannot create executables
- undefined macro LT_SYS_SYMBOL_USCORE
- possibly undefined macro: AC_PROG_LD
- all is not a valid value for orientation
- orientation have an invalid value
- build.gradle : 79: Unexpected input: '{'
- Could not resolve all files for configuration
- presplash-lottie: No such file or directory
- ssl module in Python is not available
- AttributeError: 'str' object has no attribute 'stdout'
- error: expression is not assignable
- error: possibly undefined macro: AM_ICONV
- error: failed to read PNG
- Build failed: Requested API target 31 is not available
- aaudio_DetectBrokenPlayState
- 'config.pxi' not found
- extra tap when single tap expected
- No module named 'kivy._clock'
- ValueError: 'border_radius' must have 4, got 0
- storage dir path cannot contain spaces
- java.lang.OutOfMemoryError
- No module named '_version'
- Can't exec "autopoint"
- # Cython (cython) not found
- no attribute '_JavaClass__cls_storage'
- Error compiling Cython file:
- missing optional dependency 'openpyxl'

Introduction

Python and Kivy are portable across operating systems because of POSIX, Python wheels, and pip. However Android is not POSIX-compliant, wheels are not usually available for Android, and pip is not installed on Android. Clearly many apps won't 'just work' on Android. The document is about porting a Kivy app to Android.

For a simple, well-written app that only paints the screen, and does nothing else, building for Android will be 'push button'. One can for example build 'Hello World' with the default 'buildozer.spec' file. Of course this does not describe many apps.

This document is not a substitute for Reading The Fine Manual (RTFM). Your basic resources are Buildozer, Python for Android, and Android.

Python-for-Android (p4a) is a truly amazing achievement, but there are some details to understand. The alternative is Java and the Android API, which has been shown to induce insanity in laboratory mice.

Finally, this document is my understanding as of the date above. I am not a developer in any of the Kivy sub projects (except for a few PRs). I have created a suite of Android oriented examples.

The document is guaranteed to be incomplete in some way, and may possibly be wrong in other ways. But reading it will hopefully provide you with come context with which to read the official documentation and to experiment. Those two steps are the key to insight and understanding, which in turn is key to making your idea real.

Confidence and Competence

This document aims to provide the context to enable you to take yourself up the slope on the right side of the graph.

You can get stuck on the peak on the left by failing to read the documentation, watching old YouTube videos, or using ChatGPT to write your code. If you find yourself stuck in the valley this is your opportunity to recognize (and learn from) your choices that didn't work for you.

Source: Wikimedia Commons

What is Different about Android?

POSIX

Android is not POSIX-compliant (POSIX is so deep in your assumptions about computers you probably don't know it exists).

The file system model is different; the app cannot use any directory in the file system. The app has specific private storage directories that support file operations. The app also has storage shared between apps; this is implemented as a database.

Threads are available like a desktop. Subprocess is available, but the excutable called by subprocess on the desktop almost certainly is not available.

Multi-tasking: On the desktop when an app loses focus or is minimized it continues to execute - it just doesnt see UI events; it is said to move to the background. Android is not multi-tasking, when an app is removed from the UI it pauses, and does not execute any app code - there is no background operation. Execution of separate code (with no UI), in the background requires an Android Service.

Android Lifecycle

On a desktop apps simply 'execute' and eventually 'exit'. On Android an app has an Activity Lifecycle. The Kivy Lifecycle is compliant with the Android Activity Lifecycle, so no special considerations are required for a pure Python app.

A special case is an impure Python app that calls Android Java apis. Android api calls must occur no earlier in the Kivy Lifecycle that one timestep after on_start().

In practice you may find that some Android apis are available earlier in the Kivy Lifecycle, this may vary by api and by Android version. Android documentation does not in general discuss the earliest point in the lifecycle that an api can be called. Calling from on_start() or earlier is not reliable, and may (or not!) result in unexpected behavior.

Wheels

Some Python packages are not written in Python (i.e. are not pure Python); they contain code that must be compiled. Pip provides pre-compiled packages for desktop OSes, but not for Android. P4a addresses this with recipes, but not all impure packages are available. AVOID DISAPPOINTMENT, check availability first.

A quick and easy way to determine if a package is pure Python is to go to the package on PyPI (this is where pip gets wheels), then follow the "Download Files" link, and look under "Built Distribution".

If the "Built Distribution" only contains files that end with py3-none-any.whl (for example) then the package is pure Python, and WILL NOT require a recipe.

If the "Built Distribution" contains files that end with win32.whl, and64.whl, arm64.whl or similar (for example) then the package is not pure Python, and WILL require a recipe.

If the package requires a recipe, check the list of available recipes. Note that the recipe name is not always identical to the PyPI package name, for example the "opencv-python" package has a recipe named "opencv".

If the package requires a recipe, and one does not exist, then your app is not portable to Android without extra work. Read this summary of your options.

Note that it is possible but unlikely that a pure Python package may contain OS-specific code, or depend on OS-specific third-party apps (for example ffmpeg).

Meta-information

Unlike the desktop, you must provide information about your Python code. This requirement causes everybody who doesn't understand it to crash and burn. This information must be supplied in the buildozer.spec file. It includes all the pip packages your app depends on, any file types your app depends on for data, and the Android permissions your app depends on. Meta-information may not be limited to that short list, but that list is critical.

App Security

A mobile app is different from a desktop app in that it is less likely to be physically secure from bad actors. Anybody with Android Studio and a device on which your app is installed can view most of the contents of your app. Python, Java, or C code must be decompiled to be human-readable, but this is not hard for a determined attacker.

Nothing is perfectly secure (just ask any hacker, or anybody who prints their own copies of a government's paper money). You can make confidential information harder to reverse engineer by designing your app such that:

Any trade secrets, and also the app user's private data, are only saved on a secure server.
Password vaildation is with a secure server (i.e. no passwords are built into the app).
Any temporary refresh keys are saved in app private storage, and not in the app install directory. For private storage location do not use p4a's android.app_storage_path() API call as this location is not secure

Android Storage

The view of the Android file system has changed a few times over the years. Modern Android devices physically use external storage, however the term is ambiguous as it applies to two incompatible uses cases.

Storage is either Private Storage or Shared Storage. Private Storage content is only visible to the app that created it, Shared Storage is visible to all apps. Python file operations can only be performed in Private Storage. Shared Storage is a database not a file system. Programmers used to only a desktop file system have a hard time accepting this storage architecture is different.

The storage architecture is summarized in the Android documentation. The following subsections address storage from the point of view of a Buildozer user.

Private Storage

An app can perform Python file operations (read, write, shutil) on its private storage. There are three usable storage location: the app install directory, the app storage directory, and the app cache directory. File names must be valid Linux file names.

No permissions are required to read or write an app's private storage. More on permissions below.

Do not confuse private with secure. On older Android versions it is possible for other apps to read private storage. On modern Android devices the 'App Install Directory' is not secure as Android Studio allows inspection. The 'App Storage Directory' and 'App Cache Directory' are secure.

App Install Directory

The install directory is ./. Files from the apk or aab can be accessed. An app update will overwrite this directory, so this is not a good place to save important files (though you can).

App Storage Directory

Most of the time, this is what you should use.

The app storage directory is persistent over the installed lifetime of the app. It is removed when the app is uninstalled.

The app storage directory is accessed using:

from android import mActivity

    context = mActivity.getApplicationContext()
    result =  context.getExternalFilesDir(None)   # don't forget the argument
    if result:
        storage_path =  str(result.toString())

The result in the code can be None on Android devices that have removable external storage when that storage is removed.

In addition, p4a provides a legacy storage directory. This works but does not return the same location as the Android documented getExternalFilesDir(None) above. The legacy storage directory may be used as a fallback in the case of removed external storage. The location returned by app_storage_path() is not secure, and when removed, the storage media is not secure.

from android.storage import app_storage_path
from android import mActivity

    context = mActivity.getApplicationContext()
    result =  context.getExternalFilesDir(None)   # don't forget the argument
    if result:
        storage_path = str(result.toString())
    else:
        storage_path = app_storage_path()   # NOT SECURE

App Cache Directory

The app cache directory is temporary storage. The lifetime of files in this are is managed by Android. The app storage directory is accessed using:

from android import mActivity

    context = mActivity.getApplicationContext()
    result =  context.getExternalCacheDir()
    if result:
        app_cache_directory_path =  str(result.toString())

Shared Storage

Shared storage is visible to all apps, and is persistent after an app is uninstalled. A portable app can not perform Python file operations on Shared Storage. Files are copied to and from Shared Storage.

Android Version Issues

On devices running Android 10 and later or build android.api > 28, shared storage is implemented as a database. You cannot access shared storage with Python file operations because there is no file path. The Kivy Filechooser and KivyMD file chooser only work with private storage; you must use the Android Chooser for shared storage.

On devices with Android less than 10, shared storage is a file system and you can access file with from android.storage import primary_external_storage_path. This does not work on devices running Android 10 or greater.

On devices running Android 10 or greater, shared storage is accessed via the Java MediaStore API or the Chooser API.

MediaStore

The MediaStore is a database, not a file system. The MediaStore is organized based on multiple root directories. For example 'Music', 'Movies', 'Pictures', 'Documents', and 'Downloads'.

The MediaStore files are accessed using a content URI, not a file path. Python requires a file path to access a file, not a content URI. So Python APIs such as fopen(), which depend on a file path, will fail. Content URIs are obtained from Android OS APIs - for example, the MediaStore API.

"Are you telling me I can't ....?" I'm explaining that Android shared storage is different from our expectations of a POSIX file system. Evolve or die out.

You can find examples of calling the MediaStore Java API from Python in the source for AndroidStorage4Kivy.

AndroidStorage4Kivy

An Android-version-independent Python API for shared storage is implemented in the package androidstorage4kivy.

This package is an abstraction of the MediaStore API. The abstraction is copy or delete, so files can be copies to, copied from, and deleted from shared storage. The MediaStore API, and content URIs are thus hidden. For more details see Android Shared Storage 4 Kivy's Programming Model and Android Shared Storage 4 Kivy's Shared Storage Class.

Example usage is in shared_storage_example. The example also demonstrates using the Android file Chooser, using the SharedStorage4Kivy Chooser class.

Storage Permissions

On devices running Android 10 and later, no permissions are requires to read or write an app's own shared storage or private storage. An app cannot modify another app's shared file.

If android.api < 33 reading another app's shared storage requires READ_EXTERNAL_STORAGE permission.

If android.api >= 33 use one or more of READ_MEDIA_IMAGES, READ_MEDIA_VIDEO, READ_MEDIA_AUDIO, READ_EXTERNAL_STORAGE see Android docs. Despite what it says in the Android docs, READ_EXTERNAL_STORAGE is required only to read another app's shared file when the file is part of the Documents collection.

There is one special case which is different from typical desktop usage. An app cannot read another app's file in the Downloads directory, regardless of permissions.

On devices running Android 9 and less, WRITE_EXTERNAL_STORAGE is required for any file writes. Or READ_EXTERNAL_STORAGE if the app only wants to do shared storage reads.

Shared Storage Alternatives

A little research and you will discover the MANAGE_EXTERNAL_STORAGE permission, and the requestLegacyExternalStorage flag. Neither is discussed here, due to the issues they introduce.

Sharing a file between apps

Files in Shared Storage can be shared between apps. If you want to share a file, first copy it to shared storage and then send it to an Android ShareSheet. The complement operation (receiving a shared file) requires copying the file to private storage so Python can access it.

The androidstorage4kivy package contains a ShareSheet class that invokes an Android ShareSheet, or sends a file directly to a specific app. The latter assumes that the specific app knows how to receive files of the type sent.

Examples of sending a file are in share_send_example, and receiving a file in share_receive_example.

Concurrency

Threads

Kivy executes on its 'UI thread', Android requires that its UI thread is always responsive to UI events. As a consequence, long latency operations (e.g. network access, sleep()) or computationally expensive operations must be performed in their own Python threads.

Threads must be truly asynchronous to the UI thread, so do not use join() in the UI thread. A non-UI thread may not write to a UI widget. See this basic example. A thread-safe way to return results to the UI thread is to use the @mainthread decorator, for example:

from threading import Thread
from kivy.clock import mainthread

    def run_some_function_in_thread(self, arg0):
        # note the value of args is a tuple,
        # it always contains at least one comma
        Thread(target=self.some_function, args = (arg0, ),
               daemon=True).start()

    def some_function(self, arg0):
    	# the behavior goes here, creating some result
        result = 'Greetings, Earthlings.'
        # sync a *copy* of the result with the Kivy UI thread
        self.make_thread_safe(str(result))

    @mainthread
    def make_thread_safe(self, text):
        # assign to some UI widget
        self.label.text = text

A daemon thread will automatically terminate when the main thread completes, providing all threads running at app exit are also daemon threads. Failure to always specify a daemon thread may cause an app to exit in a delayed way.

Subprocess

The Python subprocess module depends on having an ARM executable to run, this does not exist unless you build it and then chmod 744. The exception is system commands which, of course, are compiled for ARM; the executables for ls, ps, etc. are in Android's /system/bin. System commands may not have the same features as a Bash shell, and when run from subprocess.Popen have app-only permission.

There is no python3 executable, Python's sys.executable is empty. To run a Python script in a new process, we use an Android Service.

Async

Kivy async usage

Python does not allow calling (async) coroutines from (traditional) routines. Kivy is constructed of routines, however Kivy has a method that allows it to be started as an async coroutine. Thus, the Kivy and Async loops do not block one another. This does not mean any other Kivy routines become coroutines.

We normally start a Kivy app with:

ExampleApp().run()

For basic Async usage we start Kivy with (we'll show trio later):

asyncio.run(ExampleApp().async_run('asyncio'))

Alone, this does not allow us to combine routines and coroutines. An app can't directly call a coroutine from, say, a Kivy UI event such as a Button event. But an app can do this indirectly.

The details are different for the trio and asyncio packages. But the approach is the same, a co-rountine is scheduled on the async loop from a routine.

trio

Trio is an alternative async library to Python's built-in asyncio.

Using trio, a coroutine is scheduled with nursery.start_soon():

from kivy.app import App
from kivy.uix.label import Label
import trio

class ExampleApp(App):
    def __init__(self, nursery):
        super().__init__()
        self.nursery = nursery

    def build(self):
        return Label(text = 'Greetings Earthlings')

    def on_start(self):
        print("Kivy app started")
        self.start_async_function()

    def start_async_function(self):
        self.nursery.start_soon(self.my_async_function) # starts coroutine

    async def my_async_function(self):
        print("woohooo running async function on kivy app")
        await self.another_async_function()

    async def another_async_function(self):
        print("another async function")

# Start kivy app as an asynchronous task
async def main():
    async with trio.open_nursery() as nursery:
        await ExampleApp(nursery).async_run("trio") # start Kivy
        nursery.cancel_scope.cancel()

trio.run(main)              # note this is a reference to main

Thanks to @Hamburguesa for this one.

asyncio

Using asyncio, a coroutine is scheduled with asyncio.create_task():

from kivy.app import App
from kivy.uix.label import Label
import asyncio

class ExampleApp(App):
    
    def build(self):
        return Label(text = 'Greetings Earthlings')

    def on_start(self):
        print("Kivy app started")
        asyncio.create_task(self.my_async_function())
    
    async def my_async_function(self):
        print("woohooo running async function on kivy app")
        await self.another_async_function()

    async def another_async_function(self):
        print("another async function")
        
# Start kivy app as an asynchronous task
asyncio.run(ExampleApp().async_run('asyncio'))

Android Service

An Android Service performs operations that are not related to the UI. In the context of Kivy, an Android service is a Python script that executes in its own process.

A service is a Python script, not a Kivy App. You can use some functions from the Kivy package, but nothing that depends on an instantiated Kivy App class. There is no Kivy event loop (so no Clock), there is no SDL2 (so no codecs). Don't even think about instantiating a Kivy App class (there is no Window). Most Kivy functions will not work in a stand-alone Python script that does not contain an instantiated App.

There are three Kivy examples:

The first is a basic example, the second illustrates multiple services, and the third a service that is persistent regardless of app state.

OSC is a good package for message passing between app and service. However it is not designed for passing large data; consider using the file system in this case. OSC requires INTERNET permission.

Specifying a Service

We assign the service a name, and associate this with script file name in buildozer.spec. The service name must be a valid Java class name. The first character and no other character must be upper case. In the sample below the_service.py is the name of the script, and Worker is the name we give the service.

# (list) List of service to declare
services = Worker:the_service.py

We start the service from an app using the fully qualified service name, which is the app package name, with '.Service' and the service name appended:

from android import mActivity

   def start_service(self, name):
       context =  mActivity.getApplicationContext()
       service_name = str(context.getPackageName()) + '.Service' + name
       service = autoclass(service_name)
       service.start(mActivity,'')   # starts or re-initializes a service

   self.start_service('Worker') # starts a service

service_name is the name of a Java class implementing the service, which in turn executes the file the_service.py.

Stop a service by sending a message (using OSC) from the app to the service, to terminate the service's event loop.

## Inside the service
from android.config import SERVICE_CLASS_NAME
PythonService = autoclass(SERVICE_CLASS_NAME)

    self.mService = PythonService.mService
    self.loop_running = True

    # Loop
    while self.loop_running:   # set False in response to some message
        sleep(0.1)
    self.mService.stopSelf()

Some documentation shows stopping a service from the app. But it does not work in the general case as the app cannot always know the service state, only Android knows the service state

   # This does not work with a sticky foreground service
   self.service.stop(self.mActivity)

More generally check if the service is already running before starting it. An already running service will loose it's internal state if it is started again. This is required in the case of a persistent ('sticky') service, as at on_start the app cannot know if the service is running without testing for its existance.

    def get_service_name(self, name):
        context =  mActivity.getApplicationContext()
        return str(context.getPackageName()) + '.Service' + name

    def service_is_running(self, name):
        service_name = self.get_service_name(name)
        context =  mActivity.getApplicationContext()
        manager = cast('android.app.ActivityManager',
                       mActivity.getSystemService(context.ACTIVITY_SERVICE))
        for service in manager.getRunningServices(100):
            if service.service.getClassName() == service_name:
                return True
        return False
           
    def start_service_if_not_running(self, name):
        if self.service_is_running(name):
            return
        service = autoclass(self.get_service_name(name))
        service.start(mActivity,'round_music_note_white_24',
                      'Music Service','Started','')

When debugging, the default Python filter excludes any print statements in the service. To see output from the service use the adb logcat -s option, for example adb logcat -s Worker. Note, that name parameter is the name of the service with only the first character capitalized, exactly as it appears in buildozer.spec .

Within a service, the service's Android activity can be obtained using:

from android.config import SERVICE_CLASS_NAME

    PythonService = autoclass(SERVICE_CLASS_NAME)
    mActivity = PythonService.mService

Service Lifetime

Three types of service are available. The difference between them is the service lifetime allowed by the OS. The service type is specified in buildozer.spec.

Background Service

A background service is generally "short lived" as defined by the OS, its lifetime is never longer than the lifetime of the app that started it. A background service is specified in buildozer.spec with:

# (list) List of service to declare
services = Worker:the_service.py

There is an API for restarting a background service killed by the OS: setAutoRestartService().

Foreground Service

A foreground service's lifetime is no longer than its app's lifetime. When the app stops (not pauses) the service stops. A foreground service is specified in buildozer.spec with:

# (list) List of service to declare
services = Worker:the_service.py:foreground

# (list) Permissions
android.permissions = FOREGROUND_SERVICE

A notification icon may be created in the task bar, see next section.

Sticky Foreground Service

A sticky foreground service lifetime is nominally unconstrained. An app may stop and start (not just pause) and resume communication with a sticky foreground service. An app is responsible for terminating a sticky foreground service, especially if the service is energy intensive. A sticky foreground service is specified in buildozer.spec with:

# (list) List of service to declare
services = Worker:the_service.py:foreground:sticky

# (list) Permissions
android.permissions = FOREGROUND_SERVICE

A notification icon may be created in the task bar, see next section.

Because an app may stop and restart while a sticky foreground service is running, the app may not contain valid dynamic information about the service. Importantly, a reference to the instance of the service saved in a class variable will be None when the app restarts. The restart-stop code above re-initializes the service to obtain a new reference to the service so that it can be stopped.

Bound Service

There is no built-in p4a support for a bound service.

Service Notifications

For android.api < 33, a foreground service always places a notification icon in the task bar. Depending on Android device version there may be an up-to-10-second delay in the appearance of the icon. This delay is an Android 'feature' and does not indicate that the foreground service has not started.

For android.api >= 33, a foreground service only places a notification icon in the task bar if POST_NOTIFICATIONS permission is specified in buildozer.spec and as a run-time permission. If you do not do this, app behavior will vary with device version. See the Android documentation and App Permissions. No notification does not mean the service is not started.

The default icon, and the notification title and text, can be changed by specifying three additional string arguments.

  service.start(mActivity, 'icon_resource_name', 'Title', 'Text', '')

'icon_resource_name' is the name of an Android resource. See android.add_resources in buildozer.spec. Remember to consider icon size.

For example adding icon resources from a local directory named 'res_icons':

android.add_resources =
    res_icons/all_inclusive.xml:mipmap,
    res_icons/align_vertical_top.png:drawable

And use one as:

    service.start('all_inclusive', 'Important News', 'Suddenly, nothing happened.', '')

p4a Service Implementation

If you want to understand the implementation of services in more detail, read the code: PythonService.java, Service.tmpl.java, and build.py.

App Permissions

Android restricts access to many features. An app must declare the permissions it requires. There are two different declarations: manifest and user. User permissions are a subset of manifest permissions.

The full list of permissions is documented by Google. In general, you must research the permissions needed by your app. Resist the temptation to blindly guess.

Note: starting with Android API 33, the names of the shared storage permissions changed. See Storage Permissions.

Manifest permissions

Manifest permissions are declared in the buildozer.spec file. Common examples are: CAMERA, INTERNET, BLUETOOTH_SCAN, RECORD_AUDIO. Apps that scan Bluetooth or scan Wifi may require multiple permissions.

For example: If the app connects to a network, add INTERNET permission.

WRITE_EXTERNAL_STORAGE is never required for api >= 30. [Learn more.]

READ_EXTERNAL_STORAGE for api >= 33 this is only required to read another app's shared file in the Documents collection. [Android docs. Note the docs to do not mention the case described here.]

User permissions

Any app manifest permission documented as having "Protection level: dangerous" additionally requires a user permission. From Python, this is initiated with a request_permissions() call. User permission requests are seen as the dialog that Android apps present to the user. Of the four manifest permissions listed above, three are "dangerous".

Many old Kivy examples show request_permissions() at the top of main.py. On newer versions of Android this will lead to unexpected behavior, because it violates the Kivy Lifecycle.

Currently request_permissions() can only be called after (not from) on_start(), or from build(), and can only be called once per time step. Generally calling after on_start simplifies the app control logic for handling both the 'request' case and the 'previously granted' case; of course, the user may deny permission and the app must handle this case.

from android.permissions import request_permissions, check_permission, Permission

     request_permissions([Permission.CAMERA, Permission.RECORD_AUDIO])

     ok = check_permission(Permission.RECORD_AUDIO)

An implementation example is the AndroidPermissions class which encapsulates permission behavior. You can copy this file and modify the actual permissions for your app. Then instantiate the class like this:

    def on_start(self):
        self.dont_gc = AndroidPermissions(self.start_app)  

    def start_app(self):
        self.dont_gc = None
	# use whatever required permission

Note that the App class variable self.dont_gc delays garbage collection. It is critically important.

Finally, it is normal Android behavior that if a user denies permission, it may not be possible to grant that permission from the App. In this case, the user must grant the permission from the Android Settings panel for the app.

Buildozer and p4a

Install

The current release version of Buildozer is 1.5. By default, Buildozer always uses the current release version of python-for-android.

Buildozer runs on Linux. Buildozer also runs on a Mac, but the number of users is small and this is reflected in the availability of help.

It does not run on native Windows. Windows users need a Linux virtual machine such as Microsoft's WSL, Google's Colaboatory (Colab), or Oracle's VirtualBox to run Buildozer. (Most users use WSL or Colab).

Read Buildozer's installation documentation. Really.

There is an obsolete Docker image. DO NOT USE IT. The Docker image is not maintained.

If building on WSL, always build the project in a directory on the Linux partition (somewhere under WSL cd ~). You will have to copy your project from the Windows partition to the Linux partition. Never build the project in a directory on the Windows partition (usually /mnt/c/ or /mnt/d/). This may give unpredictable results, and builds that are five to ten times slower than on the Linux partition.

Try Hello World

Create a project directory and cd to it: mkdir ~/hello; cd ~/hello.
Create main.py containing the Kivy Hello World app.
Run buildozer init - this will create a buildozer.spec default template. Edit it to say that android.api=33.
Run buildozer android debug. This will take a while, especially the first time.
A successful build completes showing this on the terminal:

# Android packaging done!
# APK myapp-0.1-arm64-v8a_armeabi-v7a-debug.apk available in the bin directory

An unsuccessful build of this example almost certainly means the install instructions, or these instructions, were not followed.
Install the app on your phone. Learn how..

Changing `buildozer.spec`

Note that Buildozer allows specification of build files, versions, and options; but unlike most other build tools it does not do version management of your project options. If buildozer.spec is changed, the change probably won't propagate into the apk on the next build.

After changing the buildozer.spec file (or any of the dependencies) users must do an appclean.

buildozer appclean
buildozer android debug

There may be some exceptions to this. The only one I know to be safe is one can add (but not change version of, or remove) a package in the requirements list without the appclean.

If you don't change buildozer.spec, you don't need do a buildozer appclean.

There is no magic universal buildozer.spec. Its configuration depends on the functionality of your app.

Note: buildozer.spec syntax is a variant of the .ini syntax. There is no syntax checking.

Comments must start on the first non-whitespace character of a line. You can't put a comment at the end of a line containing an option.
Options and comments must not be more deeply indented than the previous options - they will be considered part of a multi-line options.

Failure to follow this syntax may result in hard-to-understand behavior.

What should I change?

Generally change as few options as possible; resist the temptation to overspecify, use the defaults as much as possible.

Change the title and package.name.
Change android.api to 33.
If the app is for distribution via a store, also change package.domain.
If the app includes data files, add any necessary file extensions in source.include_exts.
If the app uses Python packages that are normally installed with pip, add these and their dependencies to requirements.
If the app layout supports landscape, or landscape and portrait; enable the required device orientation.
Optionally add presplash.filename, and icon.filename (icon must be a .png).
Add the required Android Permissions to android.permissions. For example, if the app connects to a network add INTERNET permission.
If the app is for the Android store you may want to increase the default android.api to 34.
If you want to add Java use android.add_src, android.add_jars, android.add_aars, or for Maven Java packages android.gradle_dependencies.
Want to speedup debug builds? Remove one of the machine architectures in android.archs.

There are a lots of other options; most users should ignore these.

If Buildozer fails to compile

Find the error message

Look for an error message in the last part of the log after STDOUT: but before STDERR:. There is also a log output after STDERR:, this is supplemental information and generally does not contain the error message.
If you don't can't find the error message in STDOUT:, try looking immediately above STDOUT: for lines starting with [DEBUG].
If you can't find any message, get enough information so somebody can help you. Ask in one of the (Support) User Groups (Discord Kivy, or Google Groups Kivy). Always include the FULL LOG as a .txt file (not screen shots).

Understand the message

If you are lucky the message is self explanatory, or a quick search will explain it.
If you don't understand the message, look in Appendix H : Cryptic Error Messages.
If you still don't understand, get enough information so somebody can help you. Ask in one of the (Support) User Groups (Discord Kivy, or Google Groups Kivy). Always include BOTH the full contents of STDOUT: (or above) and full contents of STDERR: as a .txt file (not screen shots).

Some `buildozer.spec` options

RTFM, really. See the KivyMD section.

package.name

All characters must be alphanumeric or an underscore [a-zA-Z0-9_].

package.domain

All characters must be alphanumeric, an underscore, or a period [a-zA-Z0-9_.]. A period . must not be the last character. Any period . must be followed by a letter.

Do not use a domain owned by somebody else. The default value org.test is not accepted by the Android Store.

version

This must contain no more than two periods . surrounded by numeric characters. More than two periods will cause Gradle build tool to fail.

requirements

requirements basics

This is the list of pip packages (and possibly versions) that your app imports from. So this list will always contain at a minimum python3, kivy.

In addition Buildozer needs to know all the packages your packages depend on; there is no pip engine to work this out on Android. Determining these is shown in the next section.

Do not add Python system modules. Only packages you might install with pip on the desktop.

There are some pip packages that are added automatically: libffi, openssl, sqlite3, setuptools, six, pyjnius, android. There is no need to put these in requirements:

Remember that some packages need "recipes" to be supported. In an example of poor tool design, the names of some recipes do not match the PyPI package names. Use the 'Recipe Name', in place of the 'PyPI' package name.

PyPi Name	Recipe Name
python-dateutil	dateutil
mysql-python	mysql
ndg-httpsclient	ndghttpsclient
opencv-python	opencv
opencv-contrib-python	opencv_extras
protobuf-python	protobuf_cpp
leveldb	pyleveldb
spine-cython	spine
pyav	av

Version pinning

If a requirement is a package that requires a recipe, version pinning may result in a build error. Because a compile recipe is created for the version specified in the recipe, and may not apply to other versions if the compile model has changed.

Your options are to use the default version, or locally modify the recipe.

Find the Dependencies

To recursively find an installed package dependencies, use pipdeptree. Do not use pip freeze, this will cause unexpected results.

pip3 install pipdeptree

Use pipdeptree -p <packagename>, for example:

pip3 install google-cloud-firestore
pipdeptree -p google-cloud-firestore

Returns a package dependency tree. It looks like this:

google-cloud-firestore==2.5.2
  - google-api-core [required: >=1.31.5,<3.0.0dev,!=2.3.0,!=2.2.*,!=2.1.*,!=2.0.*, installed: 2.8.1]
    - google-auth [required: >=1.25.0,<3.0dev, installed: 2.6.0]
      - cachetools [required: >=2.0.0,<6.0, installed: 5.0.0]
      - pyasn1-modules [required: >=0.2.1, installed: 0.2.8]
        - pyasn1 [required: >=0.4.6,<0.5.0, installed: 0.4.8]
      - rsa [required: >=3.1.4,<5, installed: 4.8]
        - pyasn1 [required: >=0.1.3, installed: 0.4.8]	
....and so on....

Each line is a dependency. Because it is a tree and we want a list many lines may be duplicates. Remove the version information (after and including the [), remove the duplicate lines, remove the newlines, and change the - to ,.

We get the list of requirements dependencies for this package.

google-cloud-firestore, googxle-api-core, google-auth, cachetools, pyasn1-modules, pyasn1, rsa, googleapis-common-protos, protobuf, requests, chardet, idna, urllib3, google-cloud-core, proto-plus

However, this technique is only as good as the package information. And exhibits platform variations. For example if this is run on Linux the requests dependencies certifi, chardet, idna, urllib3 will not be listed. These missing dependencies will be found during debugging.

Kivy Widget Dependencies

Some Kivy widgets have requirement dependencies:

kivy.network.urlrequest needs requests, urllib3, chardet, idna, certifi
kivy.uix.video needs ffpyplayer and usually ffpyplayer_codecs
kivy.uix.video SDL2 crashes may be addressed with the following before all other import statements:

import os
os.environ["SDL_AUDIODRIVER"] = "android"

kivy.core.audio.SoundLoader needs ffpyplayer and optionally ffpyplayer_codecs

Requirements Examples

For examples see.

Using the technique described above, we get the following:

Requests

requirements = python3, kivy, requests, urllib3, chardet, idna, certifi

or

requirements = python3, kivy, requests, urllib3, charset-normalizer==2.1.1, idna, certifi

Pyrebase4

requirements = python3,kivy, pyrebase4, gcloud, googleapis-common-protos, protobuf, httplib2, pyparsing, oauth2client, pyasn1, pyasn1-modules, rsa, pycryptodome, python-jwt, jws, requests, certifi, chardet, idna, urllib3, requests-toolbelt , jwcrypto, cryptography, deprecated, wrapt

Run on Windows, the last four items were not determined automatically. Run on Linux the requests dependencies were missing. In both cases these were added during debugging.

firebase_admin

requirements = python3,kivy, firebase-admin, cachecontrol, msgpack, requests, certifi, chardet, idna, urllib3, google-api-core, google-auth, cachetools, pyasn1-modules, pyasn1, rsa, pyasn1, googleapis-common-protos, protobuf, google-api-python-client, google-auth-httplib2, httplib2, pyparsing, uritemplate, google-cloud-firestore, google-cloud-core, proto-plus, google-cloud-storage, google-resumable-media, google-crc32c

Not Pure Python

The packages you add here must be pure Python, or have a recipe in this list. If this is not the case, the options are to:

Rewrite the app using a different package.
Locally modify an existing recipe.
Create a new recipe.
Import the functionality from Java using Pyjnius.

None of these options are trivial. That is why it said AVOID DISAPPOINTMENT in the Wheels section above.

orientation

Some combination of portrait, landscape, portrait-reverse, landscape-reverse. And landscape is portrait rotated 90 degrees counter clockwise.

For all use:

orientation = portrait, landscape, portrait-reverse, landscape-reverse

fullscreen

If the fullscreen value is 1, the Status Bar is not shown. It defaults to 0 and the Status Bar is shown.

When not shown, a swipe up/down will temporarily show the Status Bar.

fullscreen = 0

source.include_exts

If the app contains any data files, for example icons. Then add the file extension to this list:

source.include_exts = py,png,jpg,kv,atlas

android.permissions

Research the Android permissions your app needs. List the permisions, for example:

android.permissions = INTERNET, CAMERA, BLUETOOTH_SCAN

Qualified permissions (only maxSdkVersion, or usesPermissionFlags) are supported by an extended syntax, for example:

android.permissions = INTERNET, CAMERA, (name=android.permission.BLUETOOTH_SCAN;usesPermissionFlags=neverForLocation)

If the app connects to a network you must include INTERNET permission.

android.api

The current buildozer default is 31, but should be "as high as possible".

android.api = 33

android.minapi

The current default is 21. For typical usage, don't change this.

android.ndk

The current default is 25b. For typical usage, don't change this.

android.sdk

This is automatically set by Buildozer to the latest supported version. For typical usage, don't change this.

android.archs

(previously android.arch)

Defaults to building both for ARM7 and ARM8.

android.archs = armeabi-v7a, arm64-v8a

This is what you want when building for the Android Store. For debugging this is probably not what you want because it almost doubles the build time. Select one that matches your debug device.

android.archs = arm64-v8a

An install message INSTALL_FAILED_NO_MATCHING_ABIS means the apk was built for a different architecture than the phone or emulator.

Most Common Issues

Some things you can do now to prevent surprises later:

Read the install instructions to re-check that all the dependencies are installed.
Re-check that the requirements in buildozer.spec are fully specified.
Re-check that each of the requirements is either pure Python or has a recipe.
The first time Buildozer is run, type y each time you are asked to accept a Google License Agreement.

Non-deterministic Behavior

Buildozer's behavior can be unpredictable in any of these cases:

It is run as root on an OS with user accounts (so Colab is OK).
It is run on an NTFS partition mounted on a Linux system, because some Python packages implement OS specific behavior based on the disk root name. WSL users: don't build your app on the Windows partition (/mnt/c/Users....).
buildozer.spec syntax is not .ini syntax.
The buildozer.spec source.exclude_dir is used, as source.include_ext has priority, so some files in the excluded directory may not be excluded.
There is a setup.py from some other build tool in the project directory.

Debugging

Install App on Android

First, connect the Android device to a desktop via USB. On the Android device, enable 'Developer Mode' (This option varies by device and tends to be well hidden. Google it.) and enable 'USB debugging'.

The app is then installed using Android Debug Bridge (adb) either indirectly from Buildozer or directly.

If Buildozer was run on a desktop OS (Linux or Mac) you can use Buildozer options to install and run the app on the device.

	buildozer android deploy run logcat

If Buildozer was run on a virtual machine, such as WSL or Colab, copy the .apk to a desktop OS, and use adb to install the app (For details on installing and using adb see Appendix A).

	adb install -r myapp-0.1-arm64-v8a-debug.apk

Successful adb/Buildozer configuration is indicated by log output similar to:

List of devices attached
0A052FDE40019P  device

If 'List of devices attached' is followed by an empty line then the configuration is incorrect. Usually because either the Android device debug options are not set, or adb is run from a virtual machine that can't see the physical USB port.

Do not install a debug apk using a file manager. Do not install a debug apk by copying it to the Android device and using a file manager to install the app. This is unreliable and will intermittently fail on an app update, requiring an uninstall and loss of user data. Also this install method does not allow viewing debug error messages.

An app that has been debugged and is ready to be distributed must be built using the release option not the debug option, and must be signed. For more details see Release Builds. An app built with the release option can be installed either via the Android Store, some other Store, or using a file manager.

Get an Error Message

On the desktop, your friends are the Python stack trace, and logging or print statements. It is no different on Android. To get these we run the debugger.

If the app has been installed on Android, search the logcat output for TraceBack. What follows is a Python stack trace, which usually indicates the cause of the issue. For example:

ModuleNotFoundError: No module named 'some-import-name'

Where 'some-import-name' is in 'some-pip-package-name', the error occurs because 'some-pip-package-name' is missing from buildozer.spec requirements. To get 'some-pip-package-name' look at the import statement in the Python code, it will typically be similar to from some-pip-package-name import some-import-name. Get the file name and line number of the import statement from the traceback.

If 'some-import-name' is a directory in your app and it contains .py files and the app was tested on Windows. Then update your Python on Windows and test the app on Windows again. (For a while MS shipped an 'improved' Python - luckily they stopped.)

Messages from the Android OS rather than from Python can usually be found by searching for backtrace. If using adb, Android messages appear by default. If using Buildozer, the messages are filtered to be Python only. To see the Android messages when using Buildozer, in buildozer.spec comment out the Python-only filter:

# (str) Android logcat filters to use
#android.logcat_filters = *:S python:D

Messages from Android can be cryptic. Most commonly they are due to a missing recipe for a Python package, Java API errors when using pyjnius, or Kivy lifecycle violations.

It is possible to debug using an emulator but this is not recomended initially, as it adds unknowns to the debug process. The emulator is useful for checking a debugged app on various devices and Android versions.

I Included Android Permissions, but....

If you think you have a permissions issue, you probably have a design issue.

Sometimes the issue is missing permissions, but you did read the Android documentation for the permitted resource so this is not you, right? Sometimes developers guess and specify too many permissions. It's not usually wrong but it is less than optimal.

Usually the issue is the wrong permissions for the Android device version or Android api version. Some permissions change name, and even meaning with versions. Because permissions are for an api, this means that apis change and you may be using the wrong api. This is a design issue.

The most common example is Storage Permissions, which may mean the design issue is understanding Android Storage apis. If you think in terms of 'external storage', this is probably you.

Another example is ACCESS_FINE_LOCATION, see the Android Bluetooth Permissions documentation.

Slow App Start

On the desktop, if you start a Kivy app from a desktop icon, the app is slower to start than say from an IDE. This is because Python has to start first. On Android, the same delay due to Python starting exists - Kivy apps can be slow to launch. On Android, the splash screen is used to distract from this delay. The splash screen is a work-around; it isn't the cause of the delay.

If your app is unusually slow to start, it is because it is doing too much work in the __init__(), build() or on_start() methods. A common symptom of this is is a black screen after the splash screen has closed but before the app displays.

This is your code, you can change this behavior. Common causes are:

monolithic kv
compute intensive Python in the above methods
blocking I/O operations in the above methods
too many autoclass() statements

Monolithic kv is an example of doing too much work in the build() method. A solution for monolithic kv is to have a kv file for each screen and to instantiate the screen manager in Python. At build() only the first screen is added to the screen manager. Other screens are built and added after on_start(), either on demand or on some schedule. This is known as "lazy loading".

Another common solution is to schedule any initial Python compute intensive, or I/O tasks to occur after on_start(), either on demand or on some schedule. I/O operations must always be implemented in a non-blocking way, for example using threading.

Autoclass is expensive in startup time, if you have 10 or more autoclass statements this may be significant on older devices. The solution is to throw out most of that clever Pyjnius code you spent so long perfecting, and move the code to a Java class in a .java file. Then reference your Java with one or two autoclass in the usual way. Include your Java in the build with Buildozer's android.add_src.

There may be other causes. It's your code.

Android Hardware

Camera

Use the third party Camera4Kivy Preview widget, and try its examples.

Other cameras libraries do not work on newer versions of Android; including OpenCV Camera, Kivy Camera and its derivatives such as Xcamera.

Keyboard

The relationship between the Android keyboard and the layout is somewhat configurable with softinput_mode. Consider Window.softinput_mode = 'below_target'.

The type of keyboard can be set with input_type for example TextInput(input_type = 'tel'). Accepted values are 'text', 'number', 'url', 'mail', 'datetime', 'tel', or 'address'.

The keyboard_suggestions property does not work on all Android devices. For a workaround, see Kivy's Focus behavior.

Back Button and Gesture

The back button or gesture is used by Android to pause an app. It has historically been used to also navigate within a Kivy app, as shown below.

Android 10 and up require that the back button/gesture can return the app to the Android home screen (i.e. pause an app).

Android 14 will show a preview of the 'Back target'. This preview probably won't work inside Kivy apps. So, using Back to navigate inside a Kivy app is probably going to be confusing to Android users.

To use for internal navigation, a back button/gesture can be detected with a test for key == 27, as shown in the documentation. The key handler must return a boolean, which determines if the event is passed to the OS.

In order to use the button for internal navigation, there must be a state in the app where back button/gesture is not consumed by the app. For example if the back button/gesture transitions between Kivy screens, from the "main" screen the app can go to the Android home screen on a back event:

class Main(ScreenManager):
    def __init__(self, **kwargs): 
        super().__init__(**kwargs)
        Window.bind(on_keyboard = self.keyboard)
        
    def keyboard(self,window,key,*args):
        if key == 27 and self.sm.current != "main":
            self.current = some_previous_screen
            return True   # key event consumed by app
        else:           
            return False  # key event passed to Android

Android Packages

The Android package

P4a provides Android specific utilities in the android package. This package is only available on Android. It is a Python interface to some Android OS APIs. These APIs only exist on Android devices and Android emulators, which is why the package is only available on Android. The package is part of p4a and you will not find it standalone on PyPi.

The package is, as they say, 'self documenting' (i.e. there isn't any documentation!) Read the code.

One (!) such utility is:

BroadcastReceiver

A Python class to receive Android Broadcasts. There are two examples WiFi Scanner and Bluetooth Scanner.

To find a file containing a list of all the Android system Broadcast actions for a particular installed android.api: on a machine where Buildozer has been run, type find ~/.buildozer -name broadcast_actions.txt.

Plyer

Plyer is an OS independent API for some non-POSIX OS features. See Supported APIs. Plyer is not well maintained.

Some Plyer modules and examples work on older Android versions, but not on newer Android versions. The Supported APIs table does not reflect this. For example Camera, Speech to text, Audio, and FileChooser do not work on newer Android versions.

The Plyer examples are the documentation.

The following Plyer modules require Manifest and run time permissions:

Module	Permissions
audio	RECORD_AUDIO
battery	BATTERY_STATS
brightness	WRITE_SETTINGS
call	CALL_PHONE
flash	CAMERA, FLASHLIGHT
gps	ACCESS_COARSE_LOCATION, ACCESS_FINE_LOCATION
sms	SEND_SMS
stt	RECORD_AUDIO
vibrator	VIBRATE

If you plan to use Plyer, and the idea of it is very appealing, first try a small test case on your target Android versions. If it does what you expect, check that all the features you need are available; as Plyer has a platform lowest-common-denominator design.

Pyjnius

Basic Pyjnius Usage

Pyjnus allows import of Java code into Python code. It is an interface to the Java API and the Android API. The Android API is only available on Android devices and emulators, so Android API calls must be debugged on Android.

from jnius import autoclass
# declare a Java Class
DownloadManager = autoclass('android.app.DownloadManager')
# Java sub classes are delimited by a '$' in place of a '.'
DownloadManagerRequest = autoclass('android.app.DownloadManager$Request')  

   # get a class constant
   visibility = DownloadManagerRequest.VISIBILITY_VISIBLE_NOTIFY_COMPLETED
   # instance a Java class
   self.request = DownloadManagerRequest(uri)
   # call a method in that class
   self.request.setNotificationVisibility(visibility)

Then use this to write code with Python syntax and semantics, and Java class semantics added. Some basic knowledge of Java semantics is required. Get over it. Android classes will require (possibly extensive) reading of the Android Developer Guide and Android Reference.

The record_audio_example is small and uses two different Android API classes. There is also a reference to the Android Java example that it is based on.

Add your own Java to the package using the Buildozer options android.add_src and android.add_jars in the buildozer.spec. Java files should be organized in sub-directories reflecting the Java package hierarchy.

Add AndroidX Java packages (or other Maven packages) using the Buildozer option android.gradle_dependencies in the buildozer.spec. See Maven AndroidX Group.

There are lots of small Java examples of using Android system APIs at www.java2s.com/Code/Android.

Note: some Kivy documentation examples are obsolete. If you see .renpy. as a sub field in an autoclass argument replace it with .kivy..

Pyjnius Memory Management

You will be using two garbage collectors working on the same heap, but they don't know each other's boundaries. Python may free a local reference to a Java object because it can't see that the object is used. Obviously this will cause the app to crash in an ugly way. So use class variables, as shown below, to indicate persistence to the Python garbage collector.

    ###### DONT DO THIS ####
    def foobar(self):
        # instance a Java class
        request = DownloadManagerRequest(uri)
        # call a method in that class
        request.setNotificationVisibility(visibility)

    ###### DO THIS ####
    def foobar(self):
        # instance a Java class
        self.request = DownloadManagerRequest(uri)
        # call a method in that class
        self.request.setNotificationVisibility(visibility)
        # Tell the Python garbage collector this will not be reused
        self.request = None

mActivity

Android Activity state is available via mActivity this may be used by the Android API. For example:

from android import mActivity

    mActivity.getWindowManager()
    mActivity.getApplicationContext()
    mActivity.getSystemService( <service type> )
    mActivity.getContentResolver()

Within a service, the service's Android mActivity can be obtained using:

from android.config import SERVICE_CLASS_NAME

    PythonService = autoclass(SERVICE_CLASS_NAME)
    mActivity = PythonService.mService

Android UI Thread

It possible, but uncommon, that Java statements must be executed on the Android UI thread. This is not the same as the Kivy UI thread, so will result in a run time error seen in the unfiltered logcat. In this case use the @run_on_ui_thread decorator, for example:

from android.runnable import run_on_ui_thread
from android import mActivity
from jnius import autoclass

SpeechRecognizer = autoclass('android.speech.SpeechRecognizer')

    @run_on_ui_thread
    def create_recognizer(self):
        self.speechRecognizer = SpeechRecognizer.createSpeechRecognizer(mActivity)

Python Java Class

Write Java class implementations in Python using PythonJavaClass, RTFM. You will need to understand Java signature format. This class implementation is only visible in Python, Java cannot see the implementation (though it can see the Java-defined interface).

Python implementations of Java classes have this general form:

from jnius import PythonJavaClass, java_method

class CallbackWrapper(PythonJavaClass):
    __javacontext__ = 'app'  # include if Java class interface is user supplied 
    __javainterfaces__ = ['org/kivy/speech/CallbackWrapper'] # Java package

    @java_method('(Ljava/lang/String;Ljava/lang/String;)V')  # Java signatures 
    def callback_data(self, key, value):
    	pass

Pyjnius Performance

The autoclass() statement adds significant latency during the app start. If the app contains more than perhaps a dozen autoclass() calls you will probably notice the extra app startup time.

The way to address this is to create a Java file that references the Java classes that were referenced with autoclass(). Then reference your Java class with autoclass(). A Java file is included in the project using Buildozer's android.add_src. If your Java file is located at <project>/src/org/me/myproject/my.java then use android.add_src = src .

Java Abstract Classes

It is not possible to import Java abstract classes or methods, as they have no implementation (abstract and implementation are Java keywords). It is not possible to provide the implementation in Python. You must write the implementation in Java and import that new class.

Java API Versions

Python for Android builds an apk with a minimum device API. Importing Java modules can invalidate this minimum. Check the Added in API level field in the class or method reference documentation.

If the app includes an .aar file, check that the version of Java used to build the aar is not newer than the version of OpenJDK you installed for Buildozer. If the aar is built with a newer Java, you will get an error message similar to this.

Calling Python from Java

The following illustrates calling a Python method (here called from_java()) from Java. In the example there is one argument which is a string. Java sees the method as having a different name, in this case callback_string().

The technique relies on passing the method inside a wrapper class. The interface of the wrapper class is defined in Java. And the implementation of this wrapper class is defined in Python. The wrapper class is initialized with the Python method to be called. Java calls a method inside an the same instance of the same wrapper class.

You are going to have to write some Java; get over it. To comprehend the following code fragments: read from top to bottom, then follow the path of the string from bottom to top.

In Python:

from jnius import autoclass, PythonJavaClass, java_method
SomeJavaClass = autoclass('org.wherever.whatever.SomeJavaClass')

class SomewhereInMyApp(somewidget):

         # instantiate the wrapper
         self.callback_instance = CallbackWrapper(self.from_java)

         # pass the class instance to Java
         SomeJavaClass(self.callback_instance)

     # the method to be called
     def from_java(self, filepath):
         print(filepath)   # prints "Greetings Earthlings"


# The wrapper implementation
class CallbackWrapper(PythonJavaClass):
    __javacontext__ = 'app'
    __javainterfaces__ = ['org/wherever/whatever/CallbackWrapper']

    def __init__(self, callback):
        super().__init__()
        self.callback = callback

    @java_method('(Ljava/lang/String;)V')        
    def callback_string(self, filepath):
        if self.callback:
            self.callback(filepath)

CallbackWrapper.java

package org.wherever.whatever;
// the wrapper interface
public interface CallbackWrapper {
    public void callback_string(String filepath);
}

The Java method generating the callback will be called from Java. The same Java need to reference the CallbackWrapper instance. Depending on the overall implementation you may need a Java wrapper to call the method and catch the result. Extra Java wrapper or not, call the Python like this:

SomeJavaClass.java

import org.wherever.whatever.CallbackWrapper;

class SomeJavaClass() {

   CallbackWrapper callbackClass;
   
   public SomeJavaClass(CallbackWrapper wrapper) {
       // self.callback_instance passed from Python
       CallbackWrapper callbackClass = wrapper;
   }

   // This would be the result of some Java callback, and not a static string.
   String javaCallBackResult = "Greetings Earthlings";

   // At last, the actual Java callback
   callbackClass.callback_string(javaCallBackResult);

}

Place the Java files in <project>/src/org/wherever/whatever/ and in buildozer.spec set android.add_src = src .

Java Listener Class

Sometimes the Java API has a listener class containing the Java callback method. The approach in the previous section is not directly applicable.

In this case, you will have to write a small amount of Java. Create a class that extends the required listener class, and initialize it with a CallbackWrapper class similar to the one in the previous section. The methods in your newly created subclass then call the callback wrapper methods.

The following code fragments are taken from the speech recognizer example where you can see the pieces assembled.

The custom Java listener, extends and overrides the default Java listener for the particular Java functionality:

public class KivyRecognitionListener implements RecognitionListener {

    private CallbackWrapper callback_wrapper;

    public KivyRecognitionListener(CallbackWrapper callback_wrapper) {	
	this.callback_wrapper = callback_wrapper;
    }       
    
    @Override
    public void onReadyForSpeech(Bundle bundle) {
	this.callback_wrapper.callback_data("onReadyForSpeech",""); 
    }

    @Override
    public void onRmsChanged(float v) {
	this.callback_wrapper.callback_data("onRmsChanged",String.valueOf(v)); 
    }

The Java part of the callback wrapper:

public interface CallbackWrapper {
    public void callback_data(String key, String value);
}

The Python part of the callback wrapper:

class CallbackWrapper(PythonJavaClass):
    __javacontext__ = 'app'
    __javainterfaces__ = ['org/kivy/speech/CallbackWrapper']

    def __init__(self, callback):
        super().__init__()
        self.callback = callback

    @java_method('(Ljava/lang/String;Ljava/lang/String;)V')        
    def callback_data(self, key, value):
        if self.callback:
            self.callback(key, value)

In Python, we then initialize the required Java functionality (in this case SpeechRecognizer) with our custom Java listener, and initialize our listener with an instance of the (PythonJavaClass) callback wrapper. In the case of SpeechRecognizer, the listener is set with a method named setRecognitionListener().

It is a characteristic of the SpeechRecognizer class that it must run on the Android UI thread, so we use the @run_on_ui_thread directive.

    @run_on_ui_thread
    def create_recognizer(self, recognizer_event_handler):
        self.speechRecognizer = \
            SpeechRecognizer.createSpeechRecognizer(mActivity)
        self.callback_wrapper = CallbackWrapper(recognizer_event_handler)
        self.speechRecognizer.setRecognitionListener(
            KivyRecognitionListener(self.callback_wrapper))  # Java

Finally, we handle the Java callbacks in Python.

Since in this case this method configures a Kivy UI Label widget, it must run on the Kivy main thread. We use the @mainthread directive, because the method was called from Java on the thread specified by @run_on_ui_thread. The "Android UI thread" is not the same thread as the thread on which Kivy UI widgets are updated.

    @mainthread
    def recognizer_event_handler(self, key, value):
        if key == 'onReadyForSpeech':
            self.status.text = 'Status: Listening.' 
        elif key == 'onBeginningOfSpeech':
            self.status.text = 'Status: Speaker Detected.'
        elif key == 'onEndOfSpeech':
	    self.status.text = 'Status: Not Listening.'

For more details and context, see the full speech recognizer example. In particular you will find the Python autoclass statements, and the Java package and import statements. Also the Java file hierarchy, and the buildozer.spec with the android.add_src directive.

Kivy Related Topics

disable_multitouch

If you use disable_multitouch to disable that nasty red dot in a desktop Kivy app, do not use it on Android (or iOS) as it will result in duplicate touch events in some cases.

from kivy.utils import platform
if platform not in ['android', 'ios']:
    from kivy.config import Config 
    Config.set('input', 'mouse', 'mouse, disable_multitouch')

Layout

A portable layout must be an elastic layout, because on a mobile device the Kivy window is defined by the screen and the screen changes between devices. Read the Android Documentation.

Setting widget properties such as size, size_hint, or orientation make the layout less elastic. But setting some of these layout constraints is required to achieve a particular layout, so portable layout is a balance between the two.

Mobile device screen resolution (dpi), screen orientation (landscape or portrait), and screen aspect ratio all impact the portability of a layout.

Screen Resolution

Screen resolution can be addressed by specifying font size in units of sp, and widget size in units of dp. See Kivy Metrics, and the Android Documentation.

Screen Orientation

Screen orientation on a desktop defaults to landscape, and on a mobile device usually defaults to portrait, but can be landscape or both. Developing a layout in landscape will not provide a good layout in portrait. Develop for your target orientation, or support both orientations as follows.

For a mobile device the available orientation is set in buildozer.spec, orientation it can be some combination of portrait, landscape, portrait-reverse, landscape-reverse.

Supporting orientation = <some list> usually requires dynamically modifying layout parameters such as size, size_hint, or orientation. Do this using a Widget's on_size() method, and testing for orientation. For example.

Screen Aspect Ratio

Window aspect ratio on a desktop defaults to 4:3, but screen aspect ratio varies widely on mobile devices typically about 16:9 to 20:9. So a portable layout must be elastic.

A truly elastic layout has only hints, and no sizes. In practice this may not look good in all cases. So we must specify the size of some widgets, but this requires the other widgets to be more elastic.

Geometry tells us there is no right answer. You can however localize issues. For example; instead of placing a UI Widiget in a BoxLayout element, place the UI Widget (centered and filling in one direction) in a RelativeLaout (or AnchorLayout) with the RelativeLayout inside the BoxLayout element. The UI Widgets spacing will locally adjust to BoxLayout changes, and the layout as a whole will scale with different screen aspect ratios. You will have to fill the RelativeLaout or AnchorLayout with some background color matching the UI Widgets, this will hide the adjustment space in the not-filled direction.

Testing Portability

To test the portability of a layout using a desktop, set the required size and dpi on app start. (Change the numbers to whatever you want).

python3 main.py --size=420x720 --dpi=200

Manually making changes to this window size quickly explores many cases. This provides a sanity check that you really have a good layout design.

Kivy Filechooser

Android storage is not organized in the same way as storage on a desktop, read about Android Storage.

Kivy Filechooser may only be used with Private Storage, and the rootpath property must be set to one of the three Private Storage locations. For example:

FileChooserListView(rootpath='.')   # install directory

from android import mActivity

    context = mActivity.getApplicationContext()
    result =  context.getExternalFilesDir(None)   
    if result:
        storage_path =  str(result.toString())
        FileChooserListView(rootpath=storage_path) # storage directory

For Shared Storage use the Android Chooser. The AndroidStorage4Kivy package provides a Python wrapper around the Android Chooser. Files in shared storage are referenced by a content URI not a file path, the package provides an API for copying between these.

KivyMD

The KivyMD widgets have the look-and-feel that Android users expect, but the Material Design rules mean you don't have the same flexibility as Kivy widgets.

Be certain to use the same version of KivyMD on the desktop and with Buildozer, as the API may change with KivyMD versions.

The KivyMD instructions for Buildozer are updated for a known KivyMD issue on some Android devices.

Kivy Lifecycle

Follow the Kivy Lifecycle, it abstracts the app behavior that Android expects.

The Kivy Lifecycle is a platform superset so on_pause() and on_resume() are never called by a desktop OS, but always called by Android. And on_stop() is always called by a desktop OS and never by Android. If the app implements on_pause() the implementation must return True otherwise the app will exit not pause.

In general Android api calls should be called no earlier than one timestep after on_start(). So code that innteracts with Android should not be 'script style' before the App class is instantiated, in a Widget's __init__(), in build(), or in on_start(). This is the conservative and safest approach, for more details see Android Lifecycle

An example is request_permissions() which must only be called after the App's on_start() method, and only one once in a given timestep.

Kivy Garden

Kivy Garden is a library of components ('flowers'). It consists of user contributions, and is mostly not maintained. Anybody who has had a garden knows a garden needs a gardener. Kivy Garden doesn't have one. Set your expectations accordingly.

For flowers that are maintained, add them to your buildozer.spec requirements as kivy_garden.flower, and in the app from kivy_garden.flower import FlowerClass replacing flower with the actual name, for example xcamera.

For flowers that are not maintained, copy the flower code to your project and edit so that it builds. Note: garden.matplotlib is an example of a flower that is not maintained. (Also, garden.matplotlib depends on matplotlib; this should be added to requirements).

There is a #garden_requirements = field in older buildozer.spec files. This is deprecated and should not be used.

Creating a Recipe

Why a Recipe

Some Python packages are not pure Python, they contain compiled code. This must be compiled for the specific platform.

Python packages are generally distributed in a wheel. This will contain pre-compiled binaries for supported platforms. Python wheels do not support Android, so to port a package to Android is must be explicitly compiled for ARM/Android.

P4a provides an API for creating package build scripts, called "recipes". The task in creating a recipe is to port existing build instructions. To create a recipe you must understand both of these:

The p4a recipe API.
The existing build instruction for the package.

Porting Overview

A recipe is simply a format required by p4a. It doesn't do much except set the environment variables for Clang, define some steps (environment, setup, build, install), and automate simple cases.

The potentially hard and unique part is understanding what you want the package's build scripts to do. Once you understand that then to automate within p4a's format is fairly simple.

Its easy to incorrectly focus one's attention on the p4a API when the real issue is understanding what you want the build scripts to do. As humans, we hope the recipe will magically make our dreams come true, because the work of understanding a build in order to port it can be hard.

By analogy, think of your self as an author of a recipe book. The easy part is formatting for the publisher (p4a recipe) . The potentially hard part is interpreting the chef's instructions (make, cmake, setup, configure.....), so you can modify the instructions for making the dish in a household kitchen.

P4A Recipe API

A recipe generally consists of two parts; a package build, and a package install.

The recipe API attempts to automate common cases such as Cython or setup.py, but likely this will not be sufficient - you will have to dig deeper.

The documentation provides an overview. Your best resource is the examples.

Porting Build Instructions

Build instructions could be a setup.py, a shell script, Make, CMake, Bazel, or something else. These instructions may be processor- or OS-specific, and usually depend on the GCC tools.

A port involves specifying the Android-NDK-supplied compiler tools (Clang and LLVM) in place of GCC tools, and patching any of the existing build scripts as necessary.

For background reading, the Build System Maintainers Guide provides some perspective of the Android build tools.

Recipe Support

This is full custom work. You can't schedule this; you aren't finished until the surprises stop. This task is for those who consider themselves self-supporting. Requests for help usually go unanswered because nobody will have experience of that specific issue in that context.

Resources

Read the Fine Manual

Really.

Don't rely on other sources; they can be obsolete.

Android for Python

Android for Python Examples contains examples of some Android features as used from Python. These examples only run on Android.

KivAds and KivMob

KivAds is a library that allows you to monetize your Kivy Apps using Google Admob. To use KivAds, minor modifications to p4a are currently required.

KivMob is a library that allows you to monetize your Kivy Apps using Google Admob. The documentation for android.gradle_dependencies needs to be updated.

Android Notifications

Android-Notification-in-Python

Android Billing

In-app billing

Other Resources

There are a lot of useful features to be found at these links:

Release Builds

Set up signing before your release build.

Setup signing

The official Android signing overview is here.

For a Buildozer build, setting up signing consists of two steps:

Create a key, do this once for an app. You will use keytool for this. Save the keystore, you will need it in the future to update the app in the store.
Tell Bulldozer to sign the app using the key. You will set environment variables to pass the information about the key to Buildozer.

Follow the Kivy signing instructions but don't just follow the instructions, read all the annotated comments by HeRo002. The instructions are flawed, but in combination with the comments they are good.

Here are some very detailed signing instructions.

If you are updating an app in the store, you must have the same keystore that was previously used to submit the app to the store. Export the four keystore values in the same way as you did after you first created them. Check that the key values are exported (env | grep _KEY) as this is how the keys are passed to Buildozer.

Build the release

Check that the keys are set: env | grep _KEY, if they are not set read Setup Signing.

The Android Store requires that apps be built with a minimum API level of 33. Set

android.api = 33

To generate a multi-architecture apk or aab, android.archs specifies a list of architectures. (The legacy android.arch still works, but will be removed.)

android.archs = armeabi-v7a, arm64-v8a

A debug build always builds an .apk. A release build creates an .aab as a default. You can create a release .apk by setting:

android.release_artifact = apk

After changing buildozer.spec you must:

buildozer appclean

Build a release apk or aab with:

buildozer android release

To install an .aab locally use Bundletool, in place of adb.

Appendix A : Using adb

The easiest way to get adb is to install Android Studio.

Add something like this to your PATH: C:\Users\UserName\AppData\Local\Android\Sdk\platform-tools

Some adb commands:

adb devices
adb install -r  cameraxf-0.1-arm64-v8a-debug.apk

Android and Python messages to a file:

adb logcat -c
adb logcat > log.txt

Python messages only to the screen:

adb logcat *:S python:D

Now start your app.

Note that adb logcat does not finish; it continues logging until it is terminated.

You can also connect the device wirelessly using adb but this does not appear to work from WSL.

Appendix B : Using an emulator

It is possible to debug using an emulator but this is not recomended initially; it adds unknowns to the debug process. The emulator is useful for checking a debugged app on various devices and Android versions.

The apk must be built with buildozer.spec android.arch having the same as ABI the emulator, I find x86 works more reliably than x86_64.

Install Android Studio.

In Android Studio, go to Tools->AVD Manager

Use the 'Create Virtual Device..' button if the emulator you want is not listed.

Right click on an emulator (view details) to see it's name, for example: Nexus_4_API_21

Add something like this to your PATH: C:\Users\UserName\AppData\Local\Android\Sdk\emulator

Start an emulator using it's name

emulator @Nexus_4_API_21

Check the emulator is running using 'adb devices'. Then install an app in the emulator from adb.

Appendix C : Locally modifying a recipe

Modify an existing recipe by making a local copy. Replace RECIPE_NAME with whatever recipe you are changing:

in buildozer.spec set p4a.local_recipes = ./p4a-recipes
mkdir ./p4a-recipes
Download python-for-android
Copy the recipe you want from python-for-android/tree/develop/pythonforandroid/recipes/RECIPE_NAME to ./p4a-recipes
Change the files in a way that makes you happy
buildozer appclean
buildozer android debug

Appendix D : Debugging on WSL

As an alternative to copying the apk from the WSL file system to the main Windows file system, and running adb in Windows, one can use two copies of adb as described here.

The easiest way to get adb is to install Android Studio for both Linux Subsystem (WSL) and Windows of same Android Debug Bridge version, use adb --version command to find it out

Windows setup:

Add something like this to your PATH in Windows: C:\Users\UserName\AppData\Local\Android\Sdk\platform-tools

In cmd / pwsh, run this command and this is your server and should not be closed until you finish debugging.

adb kill-server
adb -a -P 5037 nodaemon server

Add the below environmental variable to the ~/.bashrc or ~/.zshrc , depending on your shell

Linux Subsystem (WSL) setup:

export ADB_SERVER_SOCKET=tcp:192.168.1.250:5037

Note: 192.168.1.250 is local ip of your machine find it using ipconfig in cmd

Finally, adb devices in Linux Subsystem should show your device

List of devices attached
0A052FDE40019P  device

Appendix E : Copying from private storage

To copy from app private storage on an Android device to the host computer:

Connect the device via USB, on device enable Developer Mode and USB debugging.

In Android Studio run View->Tool Windows->Device File Explorer In Device File Explorer go to /data/data/org.test.example/files or lower Right click the item and Save As

Appendix F : Install Bundletool

Bundletool depends on JRE.

Download bundletool-all-1.8.0.jar (or newer) from https://github.com/google/bundletool/releases . Save in someplace that is not the project directory.

Simplify your life:

On Linux add to .bashrc:

alias bundletool='java -jar <pathToSomeplace>/bundletool-all-1.8.0.jar'

On Windows create bundltool.bat containing:

@echo off
java -jar <pathToSomeplace>\bundletool-all-1.8.0.jar %*

Then, for example:

bundletool help

bundletool validate --bundle=Test-release-0.0.1-.aab

To install a .aab to a locally connected device use bundletool:

bundletool build-apks --mode universal --bundle bin/myapp-0.0.1-armeabi-v7a_arm64-v8a-release.aab --output ./app.apk
bundletool install-multi-apks --apks app.apk

Appendix G : Modifying p4a

Buildozer clones p4a and places a copy in <project>/.buildozer. Do not try modifying this, this is Buildozer's database - you don't control what happens there.

Local Copy

Make a local copy of p4a, but not in the <project> directory. In buildozer.spec specify where the local copy is located:

p4a.source_dir = /someplace/python-for-android-develop

Modify the local copy in a way that makes you happy. This will be cloned into <project>/.buildozer so remember to appclean after changes.

From GitHub

As an alternative to making changes locally, you can reference changes saved on GitHub. The fork must be 'public' on Github. For example if you have a p4a fork on GitHub under SomeGitHubName, and optionally some branch some_branch:

p4a.fork = SomeGitHubName

p4a.branch = some_branch

Appendix H : Cryptic Error Messages

No module named 'msvcrt'
Aidl not found
Sdkmanager is not installed
64-bit instead of 32-bit
EM_X86_64 instead of EM_AARCH64
No module named '_Socket'
weakly-referenced object
OpenCV requires Android SDK Tools
No such file or directory: 'ffmpeg'
Unsupported class file major version 62
Permission denied: '/storage/emulated/0/...'
ModuleNotFoundError: No module named 'PIL'
Requested API target 27 is not available
BUILD FAILURE: No main.py(o)
/usr/bin/gzip: 1: ELF : not found
SSL: CERTIFICATE_VERIFY_FAILED
gradlew failed!
android:exported
null pointer dereference
No module named 'android'
Hunk #1 FAILED
Kivy is too old
C compiler cannot create executables
undefined macro LT_SYS_SYMBOL_USCORE
possibly undefined macro: AC_PROG_LD
all is not a valid value for orientation
orientation have an invalid value
build.gradle : 79: Unexpected input: '{'
Could not resolve all files for configuration
presplash-lottie: No such file or directory
ssl module in Python is not available
AttributeError: 'str' object has no attribute 'stdout'
error: expression is not assignable
error: possibly undefined macro: AM_ICONV
error: failed to read PNG
Build failed: Requested API target 31 is not available
aaudio_DetectBrokenPlayState
'config.pxi' not found
extra tap when single tap expected
No module named 'kivy._clock'
ValueError: 'border_radius' must have 4, got 0
storage dir path cannot contain spaces
java.lang.OutOfMemoryError
No module named '_version'
Can't exec "autopoint"
# Cython (cython) not found
no attribute '_JavaClass__cls_storage'
Error compiling Cython file:
missing optional dependency 'openpyxl'

No module named 'msvcrt'

No module named 'msvcrt' and No module named '_posixsubprocess'

Newer versions of setuptools break the p4a build tools.

pip3 list | grep setuptools will show a version >= 60

The workaround requires that you are using a venv.

pip3 uninstall setuptools
pip3 install setuptools==58.0.0

And buildozer appclean.

Aidl not found

# Aidl not found, please install it.

Aidl is part of the Google tools. To get the tools you have to accept the Google license agreements.

Cleanup with buildozer appclean, delete ~/.buildozer, and buildozer android debug and accept the Google license agreements.

If you are Linux clueless ~ expands to your home directory you can see this with ls -a ~.

Sdkmanager is not installed

# sdkmanager path "/home/????/.buildozer/android/platform/android-sdk/tools/bin/sdkmanager" does not exist, sdkmanager is notinstalled

Sdkmanager is part of the Google tools. To get the tools you have to accept the Google license agreements.

Delete ~/.buildozer , then buildozer android debug and accept the Google license agreements.

64-bit instead of 32-bit

ImportError: dlopen failed: "/data/data/org.test.myapp/files/app/_python_bundle/site-packages/cv2/cv2.so" is 64-bit instead of 32-bit

The build process included the wrong binary file.

You can check this by changing arch from armeabi-v7a to arm64-v8a, buildozer appclean, and rebuild you will get a different error. This will say failed to link an x86_64 object, which is a more informative message.

The cause is an x86_64 binary from PyPl was used; because of a requirements specification error in buildozer.spec

One of the app requirements needs a recipe (or needs to be specified differently). See the Wheels section.

In this case the requirements for OpenCV is incorrectly specified, it should be opencv because that is the recipe name.

If this message is charset_normalizer related, in Buildozer requirements set charset-normalizer==2.1.1.

And buildozer appclean.

EM_X86_64 instead of EM_AARCH64

ImportError: dlopen failed: "<something>/_python_bundle/site-packages/<somepackage>/_binding.so" is for EM_X86_64 (62) instead of EM_AARCH64 (183)

The build process included the wrong binary file.

The cause is an x86_64 binary from PyPl was used; because of a requirements specification error in buildozer.spec

One of the app requirements needs a recipe (or needs to be specified differently). See the Wheels section.

If this message is charset-normalizer related, in Buildozer requirements set charset-normalizer==2.1.1.

And buildozer appclean.

No module named '_Socket'

Module not found error: No module named '_Socket'

Occurs with some VMs (just Colab?) in response to buildozer android deploy run

Because in most cases you can't deploy run from a VM because the VM can't see the physical USB port.

Copy the .apk to the desktop, and use adb.

weakly-referenced object

ReferenceError: weakly-referenced object no longer exists

This almost always due to a known issue in kivy==1.11.1 with Python >= 3.8

The fix for this case is to use the current Kivy.

In any other case this issue can be hard to find. The programmer is assuming an object can be reused, and the garbage collector is assuming it will not be reused. One way to create this error is to assume some third-party API is not stateful, when infact it does have state.

OpenCV requires Android SDK Tools

Android SDK Tools: OpenCV requires Android SDK Tools revision 14 or newer.

Yes, but OpenCV also requires Android SDK Tools revision 30 or older (I assume it is 30). Buildozer currently uses 31 and this revision does not contain the tools that the OpenCV build expects. Hence the misleading error message, which should be OpenCV requires Android SDK Tools revision 30 or older..

It is possible to address this with a patch to ~/.buildozer to include the older tools as described in this thread.

No such file or directory: 'ffmpeg'

Occurs when the app is using subprocess() to run ffmpeg.

There is no ffmpeg executable. You have to build it for ARM. The recipe builds a library, not an executable. After building the executable, copy it to the working directory. Android does not allow installing to the usual desktop directories.

Unsupported class file major version 62

[DEBUG]: General error during semantic analysis: Unsupported class file major version 62

Version 62 Is Java 18. Error is probably due to an added jar built with Java 18. This is not going to work.

The Java version used by p4a is the version required for the gradle version used. This can be any version between openJDK-11 and 17, the install instructions suggest 17.

Permission denied: '/storage/emulated/0/...'

PermissionError: [Errno 13] Permission denied: '/storage/emulated/0/org.test.x' - Kivy on android write and save file

This occurs on devices running Android 10 or higher. What was once known as "external strorage" is now "shared storage", and is a database not a file system. The app's "local storage" is now "private storage", private storage is still a file system. See the Android Storage section.

App file operations should occur in private storage. If you want to share the file then it must be 'copied' from private to shared storage, this requires a database 'create' operation.

The package androidstorage4kivy contains a copy_to_shared() method that implements the database create. Sample usage is here.

ModuleNotFoundError: No module named 'PIL'

ModuleNotFoundError: No module named 'PIL'

The most common cases are:

Either 'pillow' was not specified in buildozer.spec requirements, in which case it must be added.

Or buildozer has been run with root permissions. Running Buildozer as root is known to cause non deterministic behavior, this is one example.

Simply running buildozer as user is not sufficent to fix the issue. Before running buildozer with user permissions you must first cleanup the corrupted state.

cd <project directory>
sudo rm -rf .buildozer 
sudo rm -rf ~/.buildozer
# and if either of these exist:
sudo rm -rf /.buildozer 
sudo rm -rf ~/.gradle

Check also that your project files are owned by a user, and not by root.

Requested API target 27 is not available

[ERROR]: Build failed: Requested API target 27 is not available, install it with the SDK android tool.

In buildozer.spec set android.api to 33.

And buildozer appclean.

BUILD FAILURE: No main.py(o)

BUILD FAILURE: No main.py(o) found in your app directory

Things to check:

The file containing your App class is named main.py.

The project directory is the current working directory.

There is no hidden directory (the name starts with a period) in the project path will cause this failure. This is a p4a error.

An app build error, try python3 -m compileall main.py to check for errors.

/usr/bin/gzip: 1: ELF : not found

/usr/bin/gzip: 1: ELF : not found

This is due to regressive behavior in WSL 1, ref.

Check the current WSL version at the Windows Command prompt with wsl -l -v.

The fix is to upgrade to WSL 2.

SSL: CERTIFICATE_VERIFY_FAILED

[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: unable to get local issuer certificate

Check for basic errors, or explictly add a certificate reference.

Check that certifi is included in the requirements.
Check that the request to use Android's network api conforms to the Kivy Lifecycle. This may vary by Android version, but generally not before on_start().
Possibly explicitly specify the location of the certificate in an environment variable at the top of the file, before other imports except these two.

import os
import certifi
os.environ['SSL_CERT_FILE'] = certifi.where()

Possibly explicitly tell ssl where the certificate is.

import ssl
import certifi
ssl.default_ca_certs = certifi.where()

Possibly explicitly specify the location of the certificate in the requests that generates the error.

import certifi

resp = requests.get(req, cafile=certifi.where())

Also it is possible to bypass https verification, if you choose to do this understand the risks. This is for your information and not a recommendation.

import ssl
ssl._create_default_https_context = ssl._create_unverified_context

And buildozer appclean.

gradlew failed!

[WARNING]: ERROR: whatever/.buildozer/android/platform/build-arm64-v8a_armeabi-v7a/dists/appname/gradlew failed!

The Gradle error message is further up the log file. Search upwards for 'BUILD FAILED' or 'what went wrong', the error messages will be in this general area.

Generally Gradle errors are due to an incorrect Java version, Java usage errors, missing Java files, a Java jar built with a newer version of Java, missing Android Java packages, or misconfigured Android resource or configuration files. Gradle does not analyze Python errors.

And buildozer appclean.

android:exported

[DEBUG]: android:exported needs to be explicitly specified for element <whatever>

This is a Gradle error message, it is about using an obsolete version of the Android package named in the message.

You can research Android package versions at Maven, and you will need a version that is compatible which whatever Python code you are using.

null pointer dereference

DEBUG : Cause: null pointer dereference

This message is not from Python, it is from the Android run time system. Some Android API call has been corrupted. This is a memory corruption issue it may exhibit differently (or not at all) on different devices. Probably due to a misuse of Pyjnius, Plyer, or android_permissions.

ALERT There is an issue on some devices with KivyMD 1.1.1 that can cause a null pointer deference, this issue does not exist in KivyMD 1.0.2 . You will see an (unfiltered) backtrace like this:

NOTE:   /data/data/org.mac.tec2023/files/app/_python_bundle/site-packages/kivy/_event.so
DEBUG   :   NOTE:   /data/data/org.mac.tec2023/files/app/_python_bundle/site-packages/kivy/graphics/compiler.so
DEBUG   :   NOTE:   /data/data/org.mac.tec2023/files/app/_python_bundle/site-packages/kivy/graphics/instructions.so
NOTE:   /data/data/org.mac.tec2023/files/app/_python_bundle/site-packages/kivy/graphics/vbo.so

To workaround, see the KivyMD instructions or use KivyMD 1.0.2 .

Memory issues are incredibly hard to debug, the error may or may not be local to the symptom. So removing code from the app may just move the issue, not remove the issue. That doesn't mean don't cut your app down, it means it is not sufficent to see your app work - you must also understand which code of yours broke the app.

Some possibilities:

A corrupted build try an appclean. This probably it not the issue but if it is you'll save a lot of work.
Pyjnius code that does not take into account the use of two garbage collectors, modify your code.
Plyer or android_permissions calls that do not occur in the 'App functions' block of the Kivy Lifecycle. Modify your code.
It is also possible that an impure Python package that has no recipe could generate this error; though other error messages or are more likely.

And buildozer appclean.

No module named 'android'

ModuleNotFoundError: No module named 'android'

The android package is only available on Android. This error occurs on a desktop, because there is no Android API implementation. The android package is only available on Android, and is installed by p4a.

Perhaps you want platform specific code:

from kivy.utils import platform
if platform == 'android':
    import android

Hunk #1 FAILED

STDOUT:
patching file somefile
Hunk #1 FAILED

Usually this is due to version pinning a compile recipe, the error is due to pinning a version that is incompatible with the compile recipe.

Remove the version pin, or locally modify the recipe.

And buildozer appclean.

Kivy is too old

Exception: The version of Kivy installed on this system is too old. (You have 2.1.0, but the application requires 2.2.1)

This message comes from KivyMD, and is seen on all platforms. The message may not be seen and you may see an Android crash (hidden by the Python log filter), related to graphics.

Use Kivy 2.2.1, for the version of KivyMD to use, contact KivyMD support.

See also https://github.com/kivymd/KivyMD/blob/master/README.md#how-to-fix-a-shader-bug-on-an-android-device

And buildozer appclean.

C compiler cannot create executables

[DEBUG]: configure: error: C compiler cannot create executables

May occur when building libffi.

This can be due to an interaction between WSL 1 and Clang in NDK 25b.

Check your WSL version at Windows prompt with wsl -l -v.

Options:

Upgrade to WSL 2
Patch Clang as described here kivy/buildozer#1543 (comment) (EXPERTS ONLY)

Ref : microsoft/WSL#8681 kivy/buildozer#1543

And buildozer appclean.

undefined macro LT_SYS_SYMBOL_USCORE

[DEBUG]: configure.ac:215: error: possibly undefined macro: LT_SYS_SYMBOL_USCORE

Recheck that the install instructions were followed.

And buildozer appclean.

possibly undefined macro: AC_PROG_LD

configure:8578: error: possibly undefined macro: AC_PROG_LD

Recheck that the install instructions were followed.

And buildozer appclean.

all is not a valid value for orientation

[app] "all" is not a valid value for "orientation"

As of Buildozer 1.5, in buildozer.spec orientation = all must be replaced with: orientation = portrait, landscape, portrait-reverse, landscape-reverse

orientation have an invalid value

[app] "orientation" have an invalid value

Upgrade to Buildozer 1.5

build.gradle : 79: Unexpected input: '{'

build.gradle': 79: Unexpected input: '{' @ line 79, column 14.

As of Buildozer 1.5 the values of the gradle_dependencies option must not be in quotes. The previous approach was a security risk.

For example change:

android.gradle_dependencies = "org.tensorflow:tensorflow-lite:+",'org.tensorflow:tensorflow-lite-support:0.0.0-nightly'

to

android.gradle_dependencies = org.tensorflow:tensorflow-lite:+,org.tensorflow:tensorflow-lite-support:0.0.0-nightly

And buildozer appclean.

Could not resolve all files for configuration

Could not resolve all files for configuration ':debugRuntimeClasspath'.
[DEBUG]:           > Could not find "com.google.mlkit:face-detection:16.0.6".

As of Buildozer 1.5 the values of the gradle_dependencies option must not be in quotes. The previous approach was a security risk.

In the above example change:

android.gradle_dependencies = "com.google.mlkit:face-detection:16.0.6" to android.gradle_dependencies = com.google.mlkit:face-detection:16.0.6

And buildozer appclean.

presplash-lottie: No such file or directory

'--presplash-lottie', "/Home/user/dir/'.pics/4.json'",
......
FileNotFoundError: [Errno 2] No such file or directory: "/Home/user/project/'.pics/4.json'"

As of Buildozer 1.5 the values of the Lottie file path option must not be in quotes. The previous approach was a security risk.

Change: android.presplash_lottie = "./pics/4.json" to android.presplash_lottie = ./pics/4.json

And buildozer appclean.

ssl module in Python is not available

WARNING: pip is configured with locations that require TLS/SSL, however the ssl module in Python is not available.

Re-check that the Buildozer install instructions were followed https://github.com/kivy/buildozer/blob/master/docs/source/installation.rst#android-on-ubuntu-2004-and-2204-64bit

And buildozer appclean.

AttributeError: 'str' object has no attribute 'stdout'

File ".buildozer/android/platform/python-for-android/pythonforandroid/build.py", line 35, in get_targets
    targets = avdmanager('list', 'target').stdout.split('\n')
AttributeError: 'str' object has no attribute 'stdout'

Occurs because the default behavior of the Python sh package changed.

Workaround: in buildozer.spec set p4a.branch = develop.

And buildozer appclean.

error: expression is not assignable

There are two different causes, pick the one that applies:

jnius/jnius.c:55290:5: error: expression is not assignable
    ++Py_REFCNT(o);

Change the Cython version to 0.29.33 as specified in the install instructions.

And buildozer appclean.

c/_cffi_backend.c:407:23: error: expression is not assignable
        Py_REFCNT(ct) = 43;

Set p4a.branch = develop

And buildozer appclean.

error: possibly undefined macro: AM_ICONV

configure.as:109: error: possibly undefined macro: AM_ICONV

Install gettext or gettext-dev

sudo apt-get install gettext

And buildozer appclean.

error: failed to read PNG

 ERROR:/content/.buildozer/android/......../src/main/res/mipmap/icon.png: AAPT: error: failed to read PNG signature: file does not start with PNG signature.

Set icon.filename to a PNG file.

And buildozer appclean.

Build failed: Requested API target 31 is not available

[ERROR]:   Build failed: Requested API target 31 is not available, install it with the SDK android tool.

Buildozer defaults to a version of the Android tools that is no longer available, increase android.api to 33

And buildozer appclean.

aaudio_DetectBrokenPlayState

/data/app/org.test.myapp-gVqZaGUKP2suWwYkosnKNQ==/lib/arm/libSDL2.so (aaudio_DetectBrokenPlayState+72)

Add this code at the very top of your main.py

import os
from kivy.utils import platform
if platform == "android":
     os.environ["SDL_AUDIODRIVER"] = "android"

'config.pxi' not found

jnius/jnius.pyx:100:0: 'config.pxi' not found

First check for a corrupted Buildozer database: buildozer appclean and build again.

If that does not fix it, the Java install is probably mis-configured. If you are using a VM and you installed Java inside, don't do this.

Check that the Java VM is configured for the correct JDK:

for Gentoo, by using eselect.
for Arch (or it's derivatives), by using archlinux-java.

To reset the Java install: Uninstall all Java packages (this is important, don't skip it), and install the JDK as shown in the Buildozer install instructions.

And buildozer appclean.

extra tap when single tap expected

This is unexpected behavior, not an error message. It is due to using the Kivy disable_multitouch feature on a mobile device. Kivy multitouch creates a nasty red dot on the screen of a desktop, it is commonly disabled with disable_multitouch. The red dot does not occur on a mobile device, and should not be disabled on a mobile device.

Do this.

No module named 'kivy._clock'

05-22 01:24:23.273 10977 12969 I python : ModuleNotFoundError: No module named 'kivy._clock'

Follow the Buildozer install instructions.

And buildozer appclean.

ValueError: 'border_radius' must have 4, got 0

File "kivy/graphics/boxshadow.pyx", line 316, in kivy.graphics.boxshadow.BoxShadow._check_iter
I   ValueError: 'border_radius' must have 4, got 0

or

File "kivy\graphics\boxshadow.pyx", line 311, in kivy.graphics.boxshadow.BoxShadow._check_iter
TypeError: 'spread_radius' accepts only list/tuple, got <class 'float'>

This is a KivyMD issue, please ask that project.

Background:

In Kivy border_radius (introduced in 2.2.0) is a 4-tuple. https://github.com/kivy/kivy/blob/2.2.0/kivy/graphics/boxshadow.pyx#L53

The version of KivyMD you are using appears to be using it as a scalar. Ask the KivyMD folks what version of their code to use.

A quick look at the versions shows KivyMD 1.1.1 https://github.com/kivymd/KivyMD/blob/1.1.1/kivymd/uix/behaviors/elevation.py does not use border_radius. For any side effects of using this version contact KivyMD.

storage dir path cannot contain spaces

ValueError: storage dir path cannot contain spaces, please specify a path with --storage-dir

The project directory or a directory somewhere above it has a whitespace ( ) in the name, this is not supported.

Change something like /home/user/my project to /home/user/my_project or similar.

java.lang.OutOfMemoryError

Gradle fails with

[DEBUG]:   	   > java.lang.OutOfMemoryError (no error message)

This is a Java error.

It may occur due to too many builds having Gradle errors, and Gradle not freeing memory. Try rebooting the machine.

More likely it occurs because your app is too large for the Java settings. Check that you do not have any unexpected data files in your app; or simmply too many data files in your design.

To change the Java settings see the Java documentation https://docs.gradle.org/current/userguide/build_environment.html#sec:gradle_configuration_properties

You will have to create ~/.gradle/gradle.properties, and add this line:

org.gradle.jvmargs=-Xmx2g -XX:MaxMetaspaceSize=512m -XX:+HeapDumpOnOutOfMemoryError -Dfile.encoding=UTF-8

If you have to do this and your apk is larger tahn 100MB is will probably be too large for the Android Store. The above Java settings workaround will not address the constraints of the Store.

No module named '_version'

RAN: /usr/bin/python3 -c 'import _version; print(_version.__version__)'
STDOUT:
Traceback (most recent call last):
  File "<string>", line 1, in <module>
ModuleNotFoundError: No module named '_version'

Buildozer's build database is corrupted, clean it.

buildozer appclean

Can't exec "autopoint"

Can't exec "autopoint": No such file or directory at /usr/share/autoconf/Autom4te/FileUtils.pm line 345

The build of this Python package or OS library (for example, liblzma) depends on gettext, install gettext.

And buildozer appclean.

Cython (cython) not found

# Cython (cython) not found, please install it.

Recheck that the install instructions were followed.

And buildozer appclean.

no attribute '_JavaClass__cls_storage'

09-01 16:42:41.769  5119  7071 I python  :  AttributeError: 'Class' object has no attribute '_JavaClass__cls_storage'

Check the Cython version is correct. Recheck that the install instructions were followed.

And buildozer appclean.

Pinning the verion of pyjnius can cause this issue. This is not required as Pyjnius and it's correct version are always added automatically.

Remove pyjnius from buildozer.spec requirements.

And buildozer appclean.

Error compiling Cython file:

[DEBUG]:        Error compiling Cython file:
[DEBUG]:        ------------------------------------------------------------
[DEBUG]:        ...
[DEBUG]:                    raise GstPlayerException('Unable to get the bus from the pipeline')
[DEBUG]:
[DEBUG]:                gst_bus_enable_sync_message_emission(self.bus)
[DEBUG]:                if self.eos_cb or self.message_cb:
[DEBUG]:                    self.hid_message = c_bus_connect_message(
[DEBUG]:                            self.bus, _on_gstplayer_message, <void *>self)
[DEBUG]:                                      ^
[DEBUG]:        ------------------------------------------------------------
[DEBUG]:
[DEBUG]:        kivy/lib/gstplayer/_gstplayer.pyx:228:30: Cannot assign type 'void (void *, GstMessage *) except * nogil' to 'buscallback_t'. Exception values are incompatible. Suggest adding 'noexcept' to type 'void (void *, GstMessage *) except * nogil'.

The Cython version is incorrect. Recheck that the install instructions were followed.

And buildozer appclean.

missing optional dependency 'openpyxl'

In buildozer.spec requirements add et_xmlfile in addition to openpyxl.

ogretMAN/Android-for-Python-Users

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