flutter - 飞镖 flutter : How to run animation from a scoped-model?

Question

如何在作用域模型的作用域模型后代的小部件中运行动画。我这里有一个红色按钮，单击它会显示一个正方形。正方形在 3 秒后消失，这恰好很快。我想要做的是让广场在几秒钟内消失。我尝试了 AnimationController，但它需要一个“vsync:”参数，我看到它通常在 initState() 中作为“vsync: this”完成，并且在其他地方使用时会出错。

import 'package:flutter/material.dart';
import 'dart:async';
import 'package:scoped_model/scoped_model.dart';

void main() {
  runApp(new MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'scoped model Opacity',
      home: new ScopedModel<MyScopedModel>(
        model: new MyScopedModel(),
        child: new MyPage(),
      ),
    );
  }
}

class MyScopedModel extends Model {
  double myOpacity = 0.0;
  Timer myTimer;

  AnimationController myAnimationController;

  void myShowSquare() {
    myOpacity = 1.0;
    myTimer = new Timer(new Duration(seconds: 3), _removeSquare);
    notifyListeners();
  }

  void _removeSquare() {
    myOpacity = 0.0;
    myTimer.cancel();
    notifyListeners();
  }
}

class MyPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Container(
        color: Colors.grey,
        child: new ScopedModelDescendant<MyScopedModel>(
          builder: (context, child, model) => new Column(
                crossAxisAlignment: CrossAxisAlignment.center,
                children: <Widget>[
                  new GestureDetector(
                    onTap: model.myShowSquare,
                    child: new Stack(
                      alignment: Alignment.center,
                      children: <Widget>[
                        new Container(
                          constraints: new BoxConstraints.expand(
                              width: 50.0, height: 50.0),
                          color: Colors.deepOrange,
                        ),
                        new Text(
                          '+',
                          style: new TextStyle(color: Colors.black),
                        ),
                      ],
                    ),
                  ),
                  new Opacity(
                    opacity: model.myOpacity,
                    child: new Container(
                      constraints:
                          new BoxConstraints.expand(width: 50.0, 
                                height: 50.0),
                      color: Colors.amber,
                    ),
                  )
                ],
              ),
        ));
  }
}

Answer 1

我想你要找的是 FadeTransition我相信它可以为您处理淡出小部件的艰苦工作。您也可以使用 AnimatedCrossFade小部件，如果你也想改变尺寸。

但是，如果您想自己制作动画，我建议您查看 Animation documentation还有这个Animation Tutorial因为他们会详细解释它是如何工作的。