链接可在相同属性上工作的单独动画 [英] Chaining seperate animations that work on the same properties

问题描述

我看过错开动画来链接动画，但是在那里他们将一种动画用于一个小部件的属性，例如一个不透明的动画控制着淡入，但是如果我想先淡入然后再淡出相同的小部件怎么办?我的意思是我已经创建了淡入淡出的动画，并用于小部件的不透明度值，如下所示:

I have looked at Staggered animations for chaining animations but there they use one animation for one widget's properties, e.g. a opacity animation is controlling the fade in, but what if I want to first fade in and then later fade out that same widget? I mean I already have created the fade in animation and that is used for the widget opacity value like this:

_opacityDontWorry = Tween(
  begin: 0.0,
  end: 1.0,
).animate(
  CurvedAnimation(parent: _animationController, curve: Interval(0.0, 0.75, curve: Curves.easeIn)),
);

所以这两个现在像这样绑定在一起:

so those two are now bound together like this:

Opacity(
  opacity: _opacityDontWorry.value,
  child: Text("Don't worry"),
)

这项工作正常，我的不透明度逐渐淡入，但是淡入后我希望它在短暂的停顿后淡出，但是我该怎么做呢?我是否要创建一个新的Tween并用它覆盖_opacityDontWorry，或者?我什至在正确的路径上，如何链接改变小部件上相同属性的多个动画?

This work just fine and my Opacity get faded in, but after it is faded in I would like it to fade out after a short pause, but how can I do this? Do I create a new Tween and overwrite the _opacityDontWorry with that, or? Am I even on the right path here, how do I chain multiple animations that alter the same properties on a widget?

谢谢
索伦

推荐答案

您可以在Animation上使用addStatusListener.检查动画何时完成，然后在AnimationController上调用reverse().

You can use addStatusListener on your Animation. Check when the animation is completed and then call reverse() on your AnimationController.

如果需要，可以在Future.delayed()内调用reverse()进行暂停.

If you want to, you can call reverse() inside a Future.delayed() for making a pause.

我为您制作了此示例:

import 'package:flutter/material.dart';

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> with TickerProviderStateMixin {
  AnimationController _animationController;
  Animation _opacityDontWorry;

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

    _animationController = AnimationController(duration: Duration(seconds: 1), vsync: this);
    _opacityDontWorry = Tween(
      begin: 0.0,
      end: 1.0,
    ).animate(
      CurvedAnimation(parent: _animationController, curve: Curves.easeIn),
    )..addStatusListener((status) {
      if (status == AnimationStatus.completed) {
        Future.delayed(Duration(seconds: 3), () {
          _animationController.reverse();
        });
      }
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      floatingActionButton: FloatingActionButton.extended(
        label: Text('Animate'),
        onPressed: () => _animationController.forward(),
      ),
      body: Center(
        child: AnimatedBuilder(
          animation: _opacityDontWorry,
          builder: (context, widget) {
            return Opacity(
              opacity: _opacityDontWorry.value,
              child: Text("Don't worry"),
            );
          },
        ),
      ),
    );
  }
}

更新

如果需要播放此动画，然后再调用另一个动画，则可以将不透明度值提取到变量中.然后根据需要从多个连续动画中更新该值.

In case you need to play this animation, and call another one after that, you can extract the opacity value to a variable. Then update that value from as many consecutive animations as you need.

  _firstAnimation = Tween(
    begin: 0.0,
    end: 1.0,
  ).animate(
    CurvedAnimation(parent: _animationController, curve: Interval(0.0, 0.20, curve: Curves.easeIn)),
  )..addListener(() {
      setState(() => _opacity = _firstAnimation.value);
    });

  // Leave an interval pause if you need
  _secondAnimation = Tween(
    begin: 1.0,
    end: 0.0,
  ).animate(
    CurvedAnimation(parent: _animationController, curve: Interval(0.40, 0.60, curve: Curves.easeIn)),
  )..addListener(() {
      setState(() => _opacity = _secondAnimation.value);
    });

在窗口小部件的不透明度属性中，不要使用_firstAnimation.value而是使用_opacity.

In your widget's opacity property, instead of using _firstAnimation.value use _opacity.

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