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# PositionedTransition

定位控件动画,用在Stack子组件中,用法如下:

class AnimationDemo extends StatefulWidget {
  
  State<StatefulWidget> createState() => _AnimationDemo();
}

class _AnimationDemo extends State<AnimationDemo>
    with SingleTickerProviderStateMixin {
  AnimationController _animationController;
  Animation _animation;

  
  void initState() {
    _animationController =
        AnimationController(duration: Duration(seconds: 2), vsync: this);

    _animation = RelativeRectTween(
            begin: RelativeRect.fromLTRB(10.0, 10.0, 10.0, 10.0),
            end: RelativeRect.fromLTRB(100.0, 100.0, 100.0, 100.0))
        .animate(_animationController);

    //开始动画
    _animationController.forward();
    super.initState();
  }

  
  Widget build(BuildContext context) {
    return Container(
      height: 300,
      width: 300,
      color: Colors.blue,
      child: Stack(
        children: <Widget>[
          PositionedTransition(
            rect: _animation,
            child: Container(
              color: Colors.red,
            ),
          )
        ],
      ),
    );
  }

  
  void dispose() {
    _animationController.dispose();
    super.dispose();
  }
}

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效果如下: