fix Applying decoration for a table row widget will cause render exception (flutter#34285)

chunhtai · web-flow · commit ad507723ec65 · 2019-06-12T16:58:24.000-07:00
diff --git a/packages/flutter/lib/src/rendering/table.dart b/packages/flutter/lib/src/rendering/table.dart
@@ -518,6 +518,8 @@ class RenderTable extends RenderBox {
   /// the table, unlike decorations for individual cells, which might not fill
   /// either.
   List<Decoration> get rowDecorations => List<Decoration>.unmodifiable(_rowDecorations ?? const <Decoration>[]);
+  // _rowDecorations and _rowDecorationPainters need to be in sync. They have to
+  // either both be null or have same length.
   List<Decoration> _rowDecorations;
   List<BoxPainter> _rowDecorationPainters;
   set rowDecorations(List<Decoration> value) {
@@ -703,7 +705,7 @@ class RenderTable extends RenderBox {
     if (_rowDecorationPainters != null) {
       for (BoxPainter painter in _rowDecorationPainters)
         painter?.dispose();
-      _rowDecorationPainters = null;
+      _rowDecorationPainters = List<BoxPainter>(_rowDecorations.length);
     }
     for (RenderBox child in _children)
       child?.detach();
@@ -1137,6 +1139,7 @@ class RenderTable extends RenderBox {
     }
     assert(_rowTops.length == rows + 1);
     if (_rowDecorations != null) {
+      assert(_rowDecorations.length == _rowDecorationPainters.length);
       final Canvas canvas = context.canvas;
       for (int y = 0; y < rows; y += 1) {
         if (_rowDecorations.length <= y)
diff --git a/packages/flutter/test/widgets/table_test.dart b/packages/flutter/test/widgets/table_test.dart
@@ -5,6 +5,7 @@
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
+import 'package:flutter/material.dart';
 
 class TestStatefulWidget extends StatefulWidget {
   const TestStatefulWidget({ Key key }) : super(key: key);
@@ -67,6 +68,41 @@ void main() {
     await run(TextDirection.rtl);
   });
 
+  testWidgets('Table widget can be detached and re-attached', (WidgetTester tester) async {
+    final Widget table = Table(
+      key: GlobalKey(),
+      children: const <TableRow>[
+        TableRow(
+          decoration: BoxDecoration(
+              color: Colors.yellow
+          ),
+          children: <Widget>[Placeholder()],
+        ),
+      ],
+    );
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: Center(
+          child: table,
+        ),
+      ),
+    );
+    // Move table to a different location to simulate detaching and re-attaching effect.
+    await tester.pumpWidget(
+      Directionality(
+        textDirection: TextDirection.ltr,
+        child: Center(
+          child: Center(
+            child: table
+          ),
+        ),
+      ),
+    );
+
+    expect(tester.takeException(), isNull);
+  });
+
   testWidgets('Table widget - column offset (LTR)', (WidgetTester tester) async {
     await tester.pumpWidget(
       Directionality(
