颤振:从当前对象位置重新启动幻灯片动画

Question

我有一个对象SlideAnimation，每次点击屏幕都会触发。对象只是在ATM上滑动，但是当我再次点击屏幕时，动画再次从对象的原始位置开始。如何捕获对象在上一个动画中结束的位置并从那里开始执行动画？
我有以下代码用于创建幻灯片过渡：

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

而这段代码用于实际的动画：

_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，您可以使用您的_characterAnimationController。动画控制器有两个相关的方法停止和前进。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();
}
}

要在完成后扩展动画，您可以通过value重置_characterAnimationController状态(或创建新状态(并更新位置。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,
));
}