为什么 Animation Tween 总是 运行 从 0.0 到 1.0？

Question

我想用

在flutter中制作动画

  late AnimationController controller1;
  late Animation<double> animation1;

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

   controller1 = AnimationController(
      duration: const Duration(milliseconds: 700),
      vsync: this,
    );
    animation1 = Tween(begin: 50.0, end: 0.0).animate(controller1)
      ..addListener(() {
        setState(() {});
      });

    controller1.forward();
}

无论我输入哪个值作为“开始”和“结束” -

controller1.value

总是从 0.0 到 1.0。我这里有什么错误？

谢谢！

Answer 1

您应该使用 animation1.value 而不是控制器值。

@override
  void initState() {
    super.initState();
    controller = AnimationController(
      vsync: this,
      duration: const Duration(milliseconds: 350),
    );
    animation = Tween<double>(begin:50, end:0.0).animate(controller);
    animation.addListener((){
      print(animation.value);
    });
    controller.forward();
  }

输出

50 50 41.285714285714285 36.714285714285715 31.57142857142857 24.857142857142854 20.14285714285714 15.428571428571423 10.428571428571423 5.714285714285708 0.9999999999999929 0

Code example

Answer 2

我认为您想使用 animation1.value，而不是 controller1.value，您可以使用以下代码验证它:) :

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

  animation = Tween<double>(begin: 50.0, end: 0.0).animate(controller)
    ..addListener(() {
      // #enddocregion addListener
      setState(() {
        print("Animation value: ${animation.value}");

        //TODO: you can uncomment this print to see the value of the controller
        //print("Controller value: ${controller.value}");
      });
    });
  controller.forward();
}

查看官方教程了解更多信息:)

Animations tutorial

顺便说一下，由于 controller.value 从 0.0 变为 1.0，您可以将其视为一种完成百分比 :)

Answer 3

我设法使用 SlideTransition 和 FadeTransition 对其进行了排序。 我想我们应该只将 Transition 小部件用于...转换？而 Positioned 和 Opacity 之类的东西用于更多静态小部件？不确定...

它的样子：https://youtu.be/hj7PkjXrgfg

无论如何，这是替换代码，如果有人正在寻找参考：

class WeatherCloudWidget extends StatefulWidget {
  final double sunSize;
  final CloudProperties properties;

  WeatherCloudWidget({Key key, this.properties, this.sunSize})
      : super(key: key);

  @override
  State<StatefulWidget> createState() => _WeatherCloudWidget();
}

class _WeatherCloudWidget extends State<WeatherCloudWidget>
    with TickerProviderStateMixin {
  AnimationController controller;
  Animation<Offset> position;
  Animation<double> opacity;

  final alphaTween = new Tween(begin: 0.0, end: 1.0);

  @override
  initState() {
    super.initState();
    _startAnimation();
  }

  @override
  Widget build(BuildContext context) {
    // screen width and height
    final screenWidth = MediaQuery.of(context).size.width;
    final screenHeight = MediaQuery.of(context).size.height;

    final properties = widget.properties;

    var vertical = (screenHeight * 0.5) +
        (widget.sunSize * properties.verticalOffset * -1);

    var horizontal =
        (screenWidth * 0.5) + (widget.sunSize * properties.tweenEnd);

    return Positioned(
      left: horizontal,
      top: vertical,
      child: SlideTransition(
          position: position,
          child: FadeTransition(
            opacity: opacity,
            child: Image.asset(
              properties.path,
              width: properties.getScaledWidth(widget.sunSize),
              height: properties.getScaledHeight(widget.sunSize),
            ),
          )),
    );
  }

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

  void _startAnimation() {
    controller = AnimationController(
        duration: const Duration(milliseconds: 2000), vsync: this);

    position = new Tween<Offset>(
      begin: new Offset(widget.properties.tweenStart, 0.0),
      end: new Offset(0.0, 0.0),
    ).animate(new CurvedAnimation(parent: controller, curve: Curves.decelerate));

    opacity = alphaTween.animate(controller);

    controller.forward();
  }
}