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Adds READMEs for databinding and mvp-loaders
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‎todo-databinding/README.md

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# TODO-DataBinding
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It is based on the [todo-mvp](https://github.com/googlesamples/android-architecture/tree/master/todo-mvp) sample and uses the Data Binding library (currently in beta) to display data
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and bind UI elements to actions.
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It's doesn't follow a strict Model-View-ViewModel or a Model-View-Presenter
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pattern, as it uses both View Models and Presenters.
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The [Data Binding Library](http://developer.android.com/tools/data-binding/guide.html#data_objects) saves on boilerplate code allowing UI elements to be bound to a property in a
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data model.
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* Layout files are used to bind data to UI elements
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* Events are also bound with an action handler
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* Data can be observed and set up to be updated automatically when needed
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<img src="https://github.com/googlesamples/android-architecture/wiki/images/mvp-databinding.png" alt="Diagram"/>
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### Data binding
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In the todo-mvp sample, a Task description is set in the [TaskDetailFragment](https://github.com/googlesamples/android-architecture/blob/master/todo-mvp/app/src/main/java/com/example/android/architecture/blueprints/todoapp/taskdetail/TaskDetailFragment.java):
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```
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public void onCreateView(...) {
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...
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mDetailDescription = (TextView)
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root.findViewById(R.id.task_detail_description);
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}
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@Override
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public void showDescription(String description) {
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mDetailDescription.setVisibility(View.VISIBLE);
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mDetailDescription.setText(description);
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}
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```
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In this sample, the [TaskDetailFragment](https://github.com/googlesamples/android-architecture/blob/master/todo-databinding/app/src/main/java/com/example/android/architecture/blueprints/todoapp/taskdetail/TaskDetailFragment.java) simply passes the Task to the data binding:
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```
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@Override
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public void showTask(Task task) {
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mViewDataBinding.setTask(task);
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}
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```
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and the library will take care of displaying it, as defined by the layout (<code>[taskdetail\_frag.xml](https://github.com/googlesamples/android-architecture/blob/master/todo-databinding/app/src/main/res/layout/taskdetail_frag.xml)</code>)
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```
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&lt;TextView
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android:id="@+id/task_detail_description"
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...
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android:text="@{task.description}" />
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```
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### Event binding
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Data binding eliminates the need to call <code>findViewById() </code>and event binding can also help minimizing <code>setOnClickListener()</code>.
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In this CheckBox from <code>[taskdetail\_frag.xml](https://github.com/googlesamples/android-architecture/blob/master/todo-databinding/app/src/main/res/layout/taskdetail_frag.xml)</code>, the presenter is called directly when the user taps on it:
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```
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&lt;CheckBox
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android:id="@+id/task_detail_complete"
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...
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android:checked="@{task.completed}"
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android:onCheckedChanged="@{(cb, isChecked) ->
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presenter.completeChanged(task, isChecked)}" />
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```
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### Observing data
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The view that shows the list of tasks (TasksFragment) only needs to know if the
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list is empty to show the appropriate message in that case. It uses [TasksViewModel](https://github.com/googlesamples/android-architecture/blob/master/todo-databinding/app/src/main/java/com/example/android/architecture/blueprints/todoapp/tasks/TasksViewModel.java) to provide that information to the layout. When the list size is set, only the
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relevant properties are notified and the UI elements bound to those properties
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are updated.
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```
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public void setTaskListSize(int taskListSize) {
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mTaskListSize = taskListSize;
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notifyPropertyChanged(BR.noTaskIconRes);
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notifyPropertyChanged(BR.noTasksLabel);
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notifyPropertyChanged(BR.currentFilteringLabel);
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notifyPropertyChanged(BR.notEmpty);
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notifyPropertyChanged(BR.tasksAddViewVisible);
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}
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```
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## Feature components
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There are multiple ways to create the relevant parts of a feature using the
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Data Binding Library. In this case, the responsibility of each component in
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this sample is:
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* Activity: object creation
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* Fragment: interaction with framework components (options menu, Snackbar, FAB,
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Adapter for list…)
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* Presenter: receives user actions and retrieves the data from the repository. If
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it doesn't do data loading, it's calling an action handler (See [TasksItemActionHandler](https://github.com/googlesamples/android-architecture/blob/master/todo-databinding/app/src/main/java/com/example/android/architecture/blueprints/todoapp/tasks/TasksItemActionHandler.java))
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* ViewModel: Exposes data for a particular view
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Some features don't have a ViewModel ([TaskDetail](https://github.com/googlesamples/android-architecture/tree/master/todo-databinding/app/src/main/java/com/example/android/architecture/blueprints/todoapp/taskdetail), [AddEditTask](https://github.com/googlesamples/android-architecture/tree/master/todo-databinding/app/src/main/java/com/example/android/architecture/blueprints/todoapp/addedittask)) as they use the Task model directly.
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## Additional dependencies
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Data Binding Library.
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## Features
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### Testability
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#### Unit testing
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As the Data Binding Library takes care of many of the wiring that would usually
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be unit tested, the number of unit tests is lower although the test coverage
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should be similar.
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#### UI testing
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No difference with MVP.
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### Code metrics
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Compared to MVP, there are more Java classes but less code per class. Because
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some wiring is moved to layouts, there are more XML lines.
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```
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-------------------------------------------------------------------------------
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Language files blank comment code
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-------------------------------------------------------------------------------
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Java 50 1079 1552 3327 (3450 in MVP)
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XML 34 122 337 714
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-------------------------------------------------------------------------------
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SUM: 84 1201 1889 4041
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-------------------------------------------------------------------------------
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```
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### Maintainability
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#### Ease of amending or adding a feature
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Easier than MVP for small changes. A new feature might require some experience
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with the library.
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#### Learning cost
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The Data Binding library takes care of the communication between some
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components, so developers need to understand what it does and doesn't before
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making changes to the code.
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‎todo-mvp-loaders/README.md

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# TODO-MVP-Loaders
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It is based on the [TODO-MVP](https://github.com/googlesamples/android-architecture/tree/master/todo-mvp) sample and uses Loaders to get the data from the tasks repository.
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<img src="https://github.com/googlesamples/android-architecture/wiki/images/mvp-loaders.png" alt="Diagram"/>
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The advantages of Loaders, from the [Loaders documentation page](http://developer.android.com/guide/components/loaders.html), are:
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* They provide asynchronous loading of data, removing the need for callbacks in
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the repository.
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* They monitor the source of their data and deliver new results when the content
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changes, in our case, the repository.
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* They automatically reconnect to the last loader when being recreated after a
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configuration change.
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## Code
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### Asynchronous loading
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The Loaders ([TaskLoader](https://github.com/googlesamples/android-architecture/blob/master/todo-mvp-loaders/app/src/main/java/com/example/android/architecture/blueprints/todoapp/data/source/TaskLoader.java) and [TasksLoader](https://github.com/googlesamples/android-architecture/blob/master/todo-mvp-loaders/app/src/main/java/com/example/android/architecture/blueprints/todoapp/data/source/TasksLoader.java)) are responsible for fetching the data and extend AsyncTaskLoader.
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In [src/data/source/TasksLoader.java](https://github.com/googlesamples/android-architecture/blob/master/todo-mvp-loaders/app/src/main/java/com/example/android/architecture/blueprints/todoapp/data/source/TasksLoader.java):
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```
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@Override
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public List&lt;Task> loadInBackground() {
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return mRepository.getTasks();
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}
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```
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The results are received in the UI Thread, handled by the presenter.
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In [TasksPresenter.java](https://github.com/googlesamples/android-architecture/blob/master/todo-mvp-loaders/app/src/main/java/com/example/android/architecture/blueprints/todoapp/tasks/TasksPresenter.java)
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```
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@Override
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public void onLoadFinished(Loader&lt;List&lt;Task>> loader, List&lt;Task>
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data) {
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mTasksView.setLoadingIndicator(false);
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mCurrentTasks = data;
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if (mCurrentTasks == null) {
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mTasksView.showLoadingTasksError();
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} else {
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showFilteredTasks();
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}
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}
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```
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The presenter also triggers the loading the data, like in the MVP sample but in
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this case it does it through the LoaderManager:
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```
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@Override
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public void start() {
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mLoaderManager.initLoader(TASKS_QUERY, null, this);
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}
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```
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### Content observer
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After every content change in the repository, <code>notifyContentObserver()</code> is called.
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In [src/data/source/TasksRepository.java](https://github.com/googlesamples/android-architecture/blob/master/todo-mvp-loaders/app/src/main/java/com/example/android/architecture/blueprints/todoapp/data/source/TasksRepository.java):
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```
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@Override
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public void deleteTask(@NonNull String taskId) {
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mTasksRemoteDataSource.deleteTask(checkNotNull(taskId));
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mTasksLocalDataSource.deleteTask(checkNotNull(taskId));
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mCachedTasks.remove(taskId);
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// Update the UI
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notifyContentObserver();
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}
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```
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This notifies the Loader which in this case simply forces a reload of data.
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In [TasksLoader.java](https://github.com/googlesamples/android-architecture/blob/master/todo-mvp-loaders/app/src/main/java/com/example/android/architecture/blueprints/todoapp/data/source/TasksLoader.java):
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```
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@Override
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public void onTasksChanged() {
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if (isStarted()) {
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forceLoad();
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}
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}
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```
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## Additional dependencies
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This project uses the Loaders framework available from Android 3.0 (API Level
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11).
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## Features
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### Complexity - understandability
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#### Use of architectural frameworks/libraries/tools:
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No external frameworks.
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#### Conceptual complexity
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Developers need to be familiar with the Loaders framework, which is not
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trivial.
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### Testability
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#### Unit testing
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The use of the Loaders framework adds a big dependency with the Android
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framework so unit testing is harder.
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#### UI testing
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No difference with MVP.
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### Code metrics
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Compared to MVP, the only new classes are TaskLoader and TasksLoader. Parts of
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the code are simpler as Loaders take care of the asynchronous work.
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```
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-------------------------------------------------------------------------------
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Language files blank comment code
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-------------------------------------------------------------------------------
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Java 48 1085 1444 3517 (3450 in MVP)
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XML 34 97 337 601
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-------------------------------------------------------------------------------
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SUM: 82 1182 1781 4118
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-------------------------------------------------------------------------------
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```
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### Maintainability
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#### Ease of amending or adding a feature
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Similar to MVP
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#### Learning cost
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Medium as the Loaders framework is not trivial.
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