add AnimatedContainer demo

lib/my_app_meta.dart

@@ -9,6 +9,7 @@ import './my_route.dart';
 import './routes/about.dart';
 
 import './routes/animation_animated_builder_ex.dart';
+import './routes/animation_animated_container_ex.dart';
 import './routes/animation_animated_widget_ex.dart';
 import './routes/animation_basic_ex.dart';
 import './routes/animation_hero_ex.dart';
@@ -177,6 +178,7 @@ const kMyAppRoutesStructure = <MyRouteGroup>[
       BasicAnimationExample(),
       AnimatedWidgetExample(),
       AnimatedBuilderExample(),
+      AnimatedContainerExample(),
     ],
   ),
   MyRouteGroup(

lib/routes/animation_animated_container_ex.dart

@@ -0,0 +1,83 @@
+import 'dart:math';
+
+import 'package:flutter/material.dart';
+import '../my_route.dart';
+
+class AnimatedContainerExample extends MyRoute {
+  const AnimatedContainerExample(
+      [String sourceFile = 'lib/routes/animation_animated_container_ex.dart'])
+      : super(sourceFile);
+
+  @override
+  get title => 'AnimatedContainer';
+
+  @override
+  get description =>
+      'Implicit animation when container property changes, without controllers.';
+
+  @override
+  get links => {
+        'Cookbook':
+            'https://flutter.dev/docs/cookbook/animation/animated-container',
+        'Widget of the Week (YouTube)': 'https://youtu.be/yI-8QHpGIP4',
+      };
+
+  @override
+  Widget buildMyRouteContent(BuildContext context) {
+    return new _AnimatedContainerDemo();
+  }
+}
+
+class _AnimatedContainerDemo extends StatefulWidget {
+  @override
+  _AnimatedContainerDemoState createState() => _AnimatedContainerDemoState();
+}
+
+class _AnimatedContainerDemoState extends State<_AnimatedContainerDemo> {
+  final _rng = Random();
+  double _height = 100;
+  double _width = 100;
+  double _borderRadius = 8;
+  Color _color = Colors.blue;
+
+  @override
+  void initState() {
+    super.initState();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    return Column(
+      children: <Widget>[
+        AnimatedContainer(
+          margin: EdgeInsets.all(8),
+          child: FlutterLogo(),
+          // Use the properties stored in the State class.
+          width: this._width,
+          height: this._height,
+          decoration: BoxDecoration(
+            color: this._color,
+            borderRadius: BorderRadius.circular(this._borderRadius),
+          ),
+          duration: Duration(seconds: 1),
+          curve: Curves.fastOutSlowIn,
+        ),
+        RaisedButton.icon(
+          icon: Icon(Icons.update),
+          label: Text('Change random property'),
+          onPressed: () => setState(
+            () {
+              // Generate a random width and height.
+              _width = _rng.nextInt(100).toDouble() + 50;
+              _height = _rng.nextInt(100).toDouble() + 50;
+              _borderRadius = _rng.nextInt(50).toDouble();
+              // Generate a random color.
+              _color = Color.fromRGBO(
+                  _rng.nextInt(256), _rng.nextInt(256), _rng.nextInt(256), 1);
+            },
+          ),
+        ),
+      ],
+    );
+  }
+}