带有IndexedStack的AnimatedSwitcher [英] AnimatedSwitcher with IndexedStack

问题描述

我必须使用IndexedStack来维护BottomNavigationBar的小部件状态.现在，我想在切换选项卡时使用AnimatedSwitcher(或替代方法)来创建动画.我遇到了使AnimatedSwitcher在IndexedStack更改时触发的问题.我将IndexedStack作为AnimatedSwitcher的子级，这显然会导致AnimatedSwitcher不会触发，因为IndexedStack小部件没有变化，只是它的子级.

I have to use IndexedStack to maintain the state of my widgets for my BottomNavigationBar. Now i want to use AnimatedSwitcher (or an alternative) to create an animation when i switch tabs. I'm having issues getting AnimatedSwitcher to trigger on change of IndexedStack. I'm having IndexedStack as the child of AnimatedSwitcher, which obviously causes AnimatedSwitcher to not trigger because the IndexedStack widget doesn't change, only it's child.

body: AnimatedSwitcher(  
  duration: Duration(milliseconds: 200),  
  child: IndexedStack(  
    children: _tabs.map((t) => t.widget).toList(),  
    index: _currentIndex,  
  ),  
)

有什么办法解决这个问题?通过手动触发AnimatedSwitcher还是通过使用其他方法来创建动画?我还尝试过更改键，但是很明显，这导致每次创建新状态时都会创建一个新的IndexedStack，因此选项卡的状态也会丢失.

Is there any way around this issue? By manually triggering the AnimatedSwitcher, or by using a different method to create an animation? I also tried changing the key, but that obviously resulted in it creating a new IndexedStack everytime the a new state was created, and therefor the states of the tabs was lost as well.

推荐答案

如果您需要使用IndexedStack.

If you need to use IndexedStack.

您可以添加自定义动画并在更改选项卡上触发它，如下所示:

You can add custom animation and trigger it on changing tabs, like that:

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> with TickerProviderStateMixin {
  final List<Widget> myTabs = [
    Tab(text: 'one'),
    Tab(text: 'two'),
    Tab(text: 'three'),
  ];

  AnimationController _animationController;
  TabController _tabController;
  int _tabIndex = 0;
  Animation animation;

  @override
  void dispose() {
    _tabController.dispose();
    super.dispose();
  }

  @override
  void initState() {
    _tabController = TabController(length: 3, vsync: this);
    _animationController = AnimationController(
      vsync: this,
      value: 1.0,
      duration: Duration(milliseconds: 500),
    );
    _tabController.addListener(_handleTabSelection);
    animation = Tween(begin: 0.0, end: 1.0).animate(_animationController);
    super.initState();
  }

  _handleTabSelection() {
    if (!_tabController.indexIsChanging) {
      setState(() {
        _tabIndex = _tabController.index;
      });
      _animationController.reset();
      _animationController.forward();
    }
  }

  @override
  Widget build(BuildContext context) {
    List<Widget> _tabs = [
      MyAnimation(
        animation: animation,
        child: Text('first tab'),
      ),
      MyAnimation(
        animation: animation,
        child: Column(
          children: List.generate(20, (index) => Text('line: $index')).toList(),
        ),
      ),
      MyAnimation(
        animation: animation,
        child: Text('third tab'),
      ),
    ];

    return Scaffold(
      appBar: AppBar(),
      bottomNavigationBar: TabBar(
        controller: _tabController,
        labelColor: Colors.redAccent,
        isScrollable: true,
        tabs: myTabs,
      ),
      body: IndexedStack(
        children: _tabs,
        index: _tabIndex,
      ),
    );
  }
}

class MyAnimation extends AnimatedWidget {
  MyAnimation({key, animation, this.child})
      : super(
          key: key,
          listenable: animation,
        );

  final Widget child;

  @override
  Widget build(BuildContext context) {
    Animation<double> animation = listenable;
    return Opacity(
      opacity: animation.value,
      child: child,
    );
  }
}

这篇关于带有IndexedStack的AnimatedSwitcher的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！