expanding_app_bar.dart

import 'package:flutter/material.dart'; void main() => runApp(new MyApp()); class MyApp extends StatelessWidget { @override Widget build(BuildContext context) { return new MaterialApp( title: 'Expanding AppBar Example', theme: new ThemeData( primarySwatch: Colors.teal, ), home: new AnimatedScaffold(), ); } } class AnimatedScaffold extends StatefulWidget { @override createState() => new AnimatedScaffoldState(); } class AnimatedScaffoldState extends State<AnimatedScaffold> with SingleTickerProviderStateMixin { AnimatedScaffoldState() { controller = new AnimationController( duration: new Duration(milliseconds: 500), vsync: this); animation = new CurvedAnimation(parent: controller, curve: Curves.easeIn); } AnimationController controller; Animation animation; bool expanded = false; _animateAppBar() { expanded ? controller.reverse() : controller.forward(); expanded = !expanded; } Widget build(BuildContext context) { return new AnimatedScaffoldBottom( animation: animation, onPress: _animateAppBar); } } class AnimatedScaffoldBottom extends AnimatedWidget { AnimatedScaffoldBottom({Key key, Animation<double> animation, this.onPress}) : super(key: key, listenable: animation); final Function onPress; static final _sizeTween = new Tween<double>(begin: 0.0, end: 300.0); @override Widget build(BuildContext context) { return new Scaffold( body: new Center( child: new Text( 'Hello World!', style: Theme.of(context).textTheme.display1, )), appBar: new AppBar( title: const Text('Expanding AppBar Example'), actions: [ new IconButton( icon: new Icon(Icons.expand_more), onPressed: onPress, ), ], bottom: new PreferredSize( preferredSize: new Size.fromHeight(_sizeTween.evaluate(listenable)), child: new Container( height: _sizeTween.evaluate(listenable), child: const Center( child: const FlutterLogo(size: 300.0), ), ), ), ), ); } }