Fix Gallery example code display initialization (#6176)

examples/flutter_gallery/lib/gallery/demo.dart

@@ -115,14 +115,13 @@ class FullScreenCodeDialogState extends State<FullScreenCodeDialog> {
   String _exampleCode;
 
   @override
-  void initState() {
-    super.initState();
-
+  void dependenciesChanged() {
     getExampleCode(config.exampleCodeTag, DefaultAssetBundle.of(context)).then((String code) {
       setState(() {
         _exampleCode = code;
       });
     });
+    super.dependenciesChanged();
   }
 
   @override

examples/flutter_gallery/lib/gallery/example_code_parser.dart

@@ -18,7 +18,8 @@ Future<String> getExampleCode(String tag, AssetBundle bundle) async {
 }
 
 Future<Null> _parseExampleCode(AssetBundle bundle) async {
-  final String code = await bundle.loadString('lib/gallery/example_code.dart');
+  final String code = await bundle.loadString('lib/gallery/example_code.dart') ??
+    '// lib/gallery/example_code.dart not found\n';
   _exampleCode = <String, String>{};
 
   final List<String> lines = code.split('\n');

examples/flutter_gallery/test/example_code_display_test.dart

@@ -0,0 +1,53 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+import 'package:flutter_gallery/gallery/app.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+Finder byTooltip(WidgetTester tester, String message) {
+  return find.byWidgetPredicate((Widget widget) {
+    return widget is Tooltip && widget.message == message;
+  });
+}
+
+void main() {
+  TestWidgetsFlutterBinding binding = TestWidgetsFlutterBinding.ensureInitialized();
+  if (binding is LiveTestWidgetsFlutterBinding)
+    binding.allowAllFrames = true;
+
+  testWidgets('Flutter gallery button example code displays', (WidgetTester tester) async {
+    // Regression test for https://github.com/flutter/flutter/issues/6147
+
+    await tester.pumpWidget(new GalleryApp());
+    await tester.pump(); // see https://github.com/flutter/flutter/issues/1865
+    await tester.pump(); // triggers a frame
+
+
+    // Scroll the Buttons demo into view so that a tap will succeed
+    final Point allDemosOrigin = tester.getTopRight(find.text('Demos'));
+    final Point buttonsDemoOrigin = tester.getTopRight(find.text('Buttons'));
+    final double scrollDelta  = buttonsDemoOrigin.y - allDemosOrigin.y;
+    await tester.scrollAt(allDemosOrigin, new Offset(0.0, -scrollDelta));
+    await tester.pump(); // start the scroll
+    await tester.pump(const Duration(seconds: 1));
+
+    // Launch the buttons demo and then prove that showing the example
+    // code dialog does not crash.
+
+    await tester.tap(find.text('Buttons'));
+    await tester.pump(); // start animation
+    await tester.pump(const Duration(seconds: 1)); // end animation
+
+    await tester.tap(find.text('RAISED'));
+    await tester.pump(); // start animation
+    await tester.pump(const Duration(seconds: 1)); // end animation
+
+    await tester.tap(byTooltip(tester, 'Show example code'));
+    await tester.pump(); // start animation
+    await tester.pump(const Duration(seconds: 1)); // end animation
+
+    expect(find.text('Example code'), findsOneWidget);
+  });
+}

packages/flutter_markdown/lib/src/markdown_raw.dart

@@ -130,9 +130,9 @@ class MarkdownBodyRaw extends StatefulWidget {
 class _MarkdownBodyRawState extends State<MarkdownBodyRaw> {
 
   @override
-  void initState() {
-    super.initState();
+  void dependenciesChanged() {
     _buildMarkdownCache();
+    super.dependenciesChanged();
   }
 
   @override