如何在 Flutter 中创建滑入和滑出动画？

Question

我正在尝试在 Flutter 中创建滑入和滑出动画。动画应该是这样的：

----- Widget slides in ---> Wait for 1 seconds -----Widget slides out of screen -->

我试过下面的代码，但我的动画卡在一个循环中。

class _MyStatefulWidgetState extends State<MyStatefulWidget> with SingleTickerProviderStateMixin {
  AnimationController _controller;
  Animation<Offset> _positionAnimation;
  Animation<double> opacityAnimation;

  @override
  void initState() {
    super.initState();
    _controller = AnimationController(
      duration: const Duration(seconds: 2),
      vsync: this,
    );

    _positionAnimation = Tween<Offset>(
      begin: const Offset(-1, 0),
      end: const Offset(0, 0.0),
    ).animate(
      CurvedAnimation(
          parent: _controller,
          curve: Curves.elasticOut),
    )..addStatusListener((status) {
        print('animation 1 status $status');
        if (status == AnimationStatus.completed) {
          _controller.reset();
        }
        if (status == AnimationStatus.dismissed) {
          _positionAnimation = Tween<Offset>(
            begin: const Offset(0, 0),
            end: const Offset(1, 0.0),
          ).animate(
            CurvedAnimation(
                parent: _controller,
                curve: Curves.elasticIn),
          )..addStatusListener((status2) {
              print('animation 2 status $status2');
            if (status == AnimationStatus.dismissed) {
              _controller.reset();
            }
            });
          _controller.forward();
        }
      });
    _controller.forward();
  }

  @override
  void dispose() {
    super.dispose();
    _controller.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return AnimatedBuilder(
      builder: _buildAnimation,
      animation: _controller,
    );
  }

  Widget _buildAnimation(BuildContext context, Widget child) {
    return Opacity(
      opacity: 1,
      child: SlideTransition(
        position: _positionAnimation,
        child: Container(
          color: Colors.blueAccent,
          height: 100,
          child: Center(
            child: Text(
              'Hello, World!',
              style: Theme.of(context).textTheme.display1,
            ),
          ),
        ),
      ),
    );
  }

使用这种方法动画陷入循环。

我无法使用交错动画，因为我正在尝试为相同的属性设置动画。（或者有没有办法在同一属性上使用交错动画？）。有什么更好的方法来实现这个吗？

Answer 1

从注释中的@pskink 代码中汲取灵感，使用以下代码实现了预期效果TweenAnimationBuilder：

class _SlideInOutWidgetState extends State<SlideInOutWidget>
    with SingleTickerProviderStateMixin {
  double startPos = -1.0;
  double endPos = 0.0;
  Curve curve = Curves.elasticOut;
  @override
  Widget build(BuildContext context) {
    return TweenAnimationBuilder(
      tween: Tween<Offset>(begin: Offset(startPos, 0), end: Offset(endPos, 0)),
      duration: Duration(seconds: 1),
      curve: curve,
      builder: (context, offset, child) {
        return FractionalTranslation(
          translation: offset,
          child: Container(
            width: double.infinity,
            child: Center(
              child: child,
            ),
          ),
        );
      },
      child: Text('animated text', textScaleFactor: 3.0,),
      onEnd: () {
        print('onEnd');
        Future.delayed(
          Duration(milliseconds: 500),
          () {
            curve = curve == Curves.elasticOut
                ? Curves.elasticIn
                : Curves.elasticOut;
            if (startPos == -1) {
              setState(() {
                startPos = 0.0;
                endPos = 1.0;
              });
            }
          },
        );
      },
    );
  }
}