动画初步

实现一些基本的动画

class _MyHomePageState extends State with SingleTickerProviderStateMixin  //具备TickerProvider特性

//定义动画初始值
AnimationController _controller;
double _size = 100;

//动画监听
  @override
  void initState() {
    super.initState();
     _controller =  AnimationController(
        vsync: this,
        duration: Duration(milliseconds: 500),
        lowerBound: 100,
        upperBound: 200)
      ..addStatusListener((AnimationStatus status) {
        if(status == AnimationStatus.completed){
          _controller.reverse();
        }else if(status == AnimationStatus.dismissed){
          _controller.forward();
        }
      })
      ..addListener(() {
        setState(() {
          _size = _controller.value;
        });
      });
  }
//body
 Center(
        child: GestureDetector(
          onTap: (){_controller.forward();},
          child: Container(
            height: _size,
            width: _size,
            color: Colors.blue,
            alignment: Alignment.center,
            child: Text("点我，开始动画"),
          ),
        ),
        )
//释放资源        
@override
  void dispose() {
    super.dispose();
    _controller.dispose();
  }