颤振：从当前物体位置重新启动SlideAnimation

Question

我有一个SlideAnimation上的对象，每当我点击屏幕时触发一个对象。物体只是向上滑动，但当我再次点击屏幕时，动画将再次从对象的原始位置开始。我将如何捕获对象在最后一个动画中结束的位置并从那里执行动画？
我已经得到了SlideTransition的创建下面的代码：

 new SlideTransition(
      child: new Container(
      child: char, 
     ), 
      position: _characterPosition, 
     ) 

而且此代码为实际动画：

_characterPosition = new FractionalOffsetTween(
    begin: const FractionalOffset(0.0, 0.0), 
    end: const FractionalOffset(0.0, -0.2), 
).animate(new CurvedAnimation(
    parent: _characterAnimationController, 
    curve: Curves.easeOut, 
) 
); 

Answer 1

在最简单的情况下，你可以使用你的_characterAnimationController。 AnimationController有两种相关的方法stop和forward。验证当前动画的状态，并调用所需的方法：

void _onTap() { 
    if (_characterAnimationController.isAnimating) { 
     _characterAnimationController.stop(canceled: false); 
    } else { 
     _characterAnimationController.forward(); 
    } 
} 

要在完成后，延长的动画，您可以通过重置value状态_characterAnimationController（或创建新的）和更新位置。完整示例：

class Home extends StatefulWidget { 
    @override 
    State createState() => new _HomeState(); 
} 

class _HomeState extends State<Home> with TickerProviderStateMixin { 
    Animation _characterPosition; 
    AnimationController _characterAnimationController; 
    FractionalOffset _beginOffset; 
    FractionalOffset _endOffset; 
    FractionalOffset _animationOffset; 

    void _restartAnimation() { 
    _characterAnimationController.value = 0.0; 
    _beginOffset = _endOffset; 
    _endOffset = _endOffset + _animationOffset; 

    setState(() { 
     _characterPosition = _generateCharacterPosition(); 
    }); 

    _characterAnimationController.forward(); 
    } 

    @override 
    void initState() { 
    _animationOffset = const FractionalOffset(0.0, 0.15); 
    _beginOffset = const FractionalOffset(0.0, 0.0); 
    _endOffset = _animationOffset; 

    _characterAnimationController = new AnimationController(
     duration: new Duration(seconds: 5), vsync: this); 
    _characterPosition = _generateCharacterPosition(); 
    } 

    @override 
    Widget build(BuildContext context) { 
    return new Material(
     child: new InkWell(
     child: new SlideTransition(
      child: new Container(
      child: new Text("Hello"), 
     ), 
      position: _characterPosition, 
     ), 
     onTap: _onTap, 
    ), 
    ); 
    } 

    void _onTap() { 
    if (_characterAnimationController.isAnimating) { 
     _characterAnimationController.stop(canceled: false); 
    } else if (_characterAnimationController.status == 
     AnimationStatus.completed) { 
     _restartAnimation(); 
    } else { 
     _characterAnimationController.forward(); 
    } 
    } 

    Animation _generateCharacterPosition() => new FractionalOffsetTween(
     begin: _beginOffset, 
     end: _endOffset, 
    ) 
      .animate(new CurvedAnimation(
     parent: _characterAnimationController, 
     curve: Curves.easeOut, 
    )); 
}