在同一属性上颤动交错动画

Question

我想为小部件的比例设置动画。 点击向下时，它应该缩小，点击向上时，它应该放大。

问题是如何在同一属性上使用交错动画？
这里有一个关于 SO 的较旧问题（链接在相同属性上工作的单独动画），但它没有有效的答案。

我尝试调整其解决方案，但问题是即使尚未达到指定的

Interval

，也会调用每个动画侦听器。

我添加了一个条件来检查

_animationFuture

是否已设置，但使用此模式，您必须为小部件中的任何正在运行的动画保留一个值，这有点麻烦。

是否有一个“本机”解决方案，您不需要解决这个问题，或者只是不支持具有相同值的多个动画？

我不想

reverse()

动画。每个补间必须能够有自定义曲线、开始值和结束值。

这是我的小部件：

class AnimatedIconButton extends StatefulWidget {

  final Widget child;

  final Function onPress;

  AnimatedIconButton({@required this.child, this.onPress}): assert(child != null);

  @override
  _AnimatedIconButtonState createState() => _AnimatedIconButtonState();
}

class _AnimatedIconButtonState extends State<AnimatedIconButton> with SingleTickerProviderStateMixin {
  AnimationController _animationController;

  Animation<double> _animationIn;
  Animation<double> _animationOut;

  double _scale = 1;

  TickerFuture _animationFuture;


  Function get onPress => widget.onPress ?? () => null;

  _tapDown(TapDownDetails details) {
    print("_tapDown progress=${_animationController.value} scale=$_scale");
    _animationFuture = _animationController.animateTo(0.5);
  }

  _tapUp(TapUpDetails details) {
    assert(_animationFuture != null);
    print("_tapUp progress=${_animationController.value} scale=$_scale");

    _animationFuture.then((_) {
      _animationFuture = null;
      _animationController.animateTo(1);
    });

  }

  @override
  void initState() {
    super.initState();

    _animationController = AnimationController(value: 0, vsync: this, duration: const Duration(milliseconds: 1500), animationBehavior: AnimationBehavior.preserve);

    _animationIn = Tween<double>(begin: 1.0, end: 0.9).animate(CurvedAnimation(
      parent: _animationController,
      curve: Interval(
        0, 0.5, curve: Curves.easeOut,
      ),
    ))..addListener(() {
      if (_animationFuture == null) return;
      print("_animationIn.value ${_animationOut.value}");
      _scale = _animationIn.value;
    });

    _animationOut = Tween<double>(begin: 0.9, end: 1).animate(CurvedAnimation(
      parent: _animationController,
      curve: Interval(
          0.5, 1, curve: Curves.elasticOut,
      ),
    ))..addListener(() {
      if (_animationFuture != null) return;
      print("_animationOut.value ${_animationOut.value}");
       _scale = _animationOut.value;
    });



  }

  @override
  void dispose() {
    _animationController.dispose();

    super.dispose();
  }

  @override
  Widget build(BuildContext context) {

    return GestureDetector(
      onTapUp: _tapUp,
      onTapDown: _tapDown,
      child: AnimatedBuilder(
        animation: _animationController,
        child: widget.child,
        builder: (_, child) {
          return Transform.scale(
            scale: _scale,
            transformHitTests: false,
            child: child,
          );
        },
      ),
    );

  }
}

Answer 1

您可以使用 TweenSequence 将多个动画交错排列。借用文档中的示例并对其进行一些更改，这是一个复制粘贴小部件，它将蓝色容器从 100x100 动画到 200x200，暂停一会儿，然后将其动画回来：

class _StaggeredState extends State<Staggered>
    with SingleTickerProviderStateMixin {
  /// Controller managing the animation
  late final AnimationController controller;

  /// The aninmation of our TweenSequence
  late final Animation<double> animation;

  /// An Animatable consisting of a series of tweens
  final Animatable<double> tweenSequence = TweenSequence<double>(
    <TweenSequenceItem<double>>[
      // Animate from .5 to 1 in the first 40/80th of this animation
      TweenSequenceItem<double>(
        tween: Tween<double>(begin: 100, end: 200)
            .chain(CurveTween(curve: Curves.ease)),
        weight: 40.0,
      ),
      // Maintain still at 1.0 for 20/80th
      TweenSequenceItem<double>(
        tween: ConstantTween<double>(200),
        weight: 20.0,
      ),
      // Animate back from 1 to 0.5 for the last 40/80th
      TweenSequenceItem<double>(
        tween: Tween<double>(begin: 200, end: 100)
            .chain(CurveTween(curve: Curves.ease)),
        weight: 40.0,
      ),
    ],
  );

  @override
  void initState() {
    super.initState();
    controller = AnimationController(
      vsync: this,
      duration: const Duration(seconds: 1),
    );

    // Animate our TweenSequence using our controller
    animation = tweenSequence.animate(controller);

    // Add a listener that calls [setState] so our widget rebuilds
    // when the animation value changes.
    controller.addListener(() => setState(() {}));

    // Set the controller to repeat indefinitely
    controller.repeat();
  }

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Center(
          child: Container(
            width: animation.value,
            height: animation.value,
            color: Colors.blue,
          ),
        ),
      ),
    );
  }
}

Answer 2

与其添加每次控制器值更改时调用

setState

的监听器，不如使用 Flutter 类

AnimatedBuilder

，将动画作为参数传递。