无法'forward ' flutter动画

Question

我有这段代码，它使用 AnimationController 和 Tween 在 [ 时沿 Z 轴旋转容器=29=] 按钮 被按下。问题是它只在第一次转发动画之后无论我按下多少次按钮它什么都不做并且容器保持静止。

curvesanimation.dart 具有所有动画逻辑

import 'package:flutter/material.dart';
import 'dart:math' as math;


class CurvedAnimationExample extends StatefulWidget {
  CurvedAnimationExample({Key key}) : super(key: key);
  @override
  CurvedAnimationExampleState createState() => CurvedAnimationExampleState();
}

class CurvedAnimationExampleState extends State<CurvedAnimationExample>
    with SingleTickerProviderStateMixin {
  Animation<double> _animation;
  AnimationController _animationController;

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

    _animationController =
        AnimationController(vsync: this, duration: Duration(seconds: 5))
          ..addListener(() {
            setState(() {});
          });

    final Animation curve =
        CurvedAnimation(parent: _animationController, curve: Curves.easeIn);

    _animation = Tween<double>(begin: 0, end: math.pi * 2).animate(curve);
  }

  void startStopAnimation() {                      
    print(_animationController.isAnimating.toString());
    if (_animationController.isAnimating)
      _animationController.stop();
    else {
      _animationController.forward();
    }
  }

  @override
  Widget build(BuildContext context) {
    return Center(
        child: Column(
      mainAxisAlignment: MainAxisAlignment.spaceEvenly,
      children: [
        Transform(
          alignment: Alignment.center,
          transform: Matrix4.identity()..rotateZ(_animation.value),
          child: Container(
            color: Colors.pinkAccent,
            width: 200,
            height: 200,
          ),
        ),
        RaisedButton(
          child: const Text("Start/Stop Animation"),
          elevation: 15,
          color: Colors.blueGrey,
          onPressed: () => startStopAnimation(),
        )
      ],
    ));
  }

  @override
  void dispose() {
    _animationController.dispose();
    print("Curved Animation Example : dispose is called");
    super.dispose();
  }
}

main.dart 文件

import 'package:flutter/material.dart';
import 'curvesanimations.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomeScaffold(
        title: "Curved Animation Example",
      ),
    );
  }
}

class MyHomeScaffold extends StatelessWidget {
  final String title;
  MyHomeScaffold({this.title});
  @override
  Widget build(BuildContext context) {
    return SafeArea(
      child: Scaffold(
        appBar: AppBar(
          title: Text(title),
        ),
        body: CurvedAnimationExample(),
      ),
    );
  }
}

Answer 1

这是因为您的动画已经到达终点。一旦到达终点就不能继续前进。一个简单的解决方法是检查动画是否已经在终点，如果是，则将其重置为起点：

void startStopAnimation() {                      
    print(_animationController.isAnimating.toString());
    if (_animationController.isAnimating)
      _animationController.stop();
    else {
      print("forward");
      if(_animationController.isCompleted) {//Check if animation is at endpoint
        _animationController.value = 0;
      }
      _animationController.forward();
    }
  }

无法'forward ' flutter动画

Unable to 'forward ' the flutter animation

dart

flutter

flutter-animation