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当使用BottomNavigationBar导航时，如何在颤动中保留窗口小部件状态？

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我正在制作一个Flutter应用程序，它将在从一个屏幕导航到另一个屏幕时保留状态，并在使用BottomNavigationBar时再次返回 . 就像它在Spotify移动应用程序中工作一样;如果您在其中一个主屏幕上导航层次结构中导航到某个级别，通过底部导航栏更改屏幕，然后更改回旧屏幕，将保留用户在该层次结构中的位置，包括保留国家 .

我把头靠在墙上，尝试各种不同的事情而没有成功 .

我想知道如何阻止 pageChooser() 中的页面，当用户点击BottomNavigationBar项目时切换，重建自己，而是保留他们已经找到的状态（页面都是有状态的Widgets） .

import 'package:flutter/material.dart';
import './page_plan.dart';
import './page_profile.dart';
import './page_startup_namer.dart';

void main() => runApp(new Recipher());

class Recipher extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Pages();
  }
}

class Pages extends StatefulWidget {
  @override
  createState() => new PagesState();
}

class PagesState extends State<Pages> {
  int pageIndex = 0;


  pageChooser() {
    switch (this.pageIndex) {
      case 0:
        return new ProfilePage();
        break;

      case 1:
        return new PlanPage();
        break;

      case 2:
        return new StartUpNamerPage(); 
        break;  

      default:
        return new Container(
          child: new Center(
            child: new Text(
              'No page found by page chooser.',
              style: new TextStyle(fontSize: 30.0)
              )
            ),
          );     
    }
  }

  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      home: new Scaffold(
        body: pageChooser(),
        bottomNavigationBar: new BottomNavigationBar(
          currentIndex: pageIndex,
          onTap: (int tappedIndex) { //Toggle pageChooser and rebuild state with the index that was tapped in bottom navbar
            setState(
              (){ this.pageIndex = tappedIndex; }
              ); 
            },
          items: <BottomNavigationBarItem>[
            new BottomNavigationBarItem(
              title: new Text('Profile'),
              icon: new Icon(Icons.account_box)
              ),
              new BottomNavigationBarItem(
                title: new Text('Plan'),
                icon: new Icon(Icons.calendar_today)
              ),
                new BottomNavigationBarItem(
                title: new Text('Startup'),
                icon: new Icon(Icons.alarm_on)
              )
            ],
          )
      )
    );
  }
}
dart flutter

2 回答

  • 1

    使用AutomaticKeepAliveClientMixin强制不处理您的标签内容 .

    class PersistantTab extends StatefulWidget {
  @override
  _PersistantTabState createState() => _PersistantTabState();
}

class _PersistantTabState extends State<PersistantTab> with AutomaticKeepAliveClientMixin {
  @override
  Widget build(BuildContext context) {
    return Container();
  }

  // Setting to true will force the tab to never be disposed. This could be dangerous.
  @override
  bool get wantKeepAlive => true;
}

    要确保标签在不需要保留时处理，请使 wantKeepAlive 返回一个类变量 . 您必须调用 updateKeepAlive() 来更新保持活动状态 .

    动态保持活动的示例：

    // class PersistantTab extends StatefulWidget ...

class _PersistantTabState extends State<PersistantTab>
    with AutomaticKeepAliveClientMixin {
  bool keepAlive = false;

  @override
  void initState() {
    doAsyncStuff();
  }

  Future doAsyncStuff() async {
    keepAlive = true;
    updateKeepAlive();
    // Keeping alive...

    await Future.delayed(Duration(seconds: 10));

    keepAlive = false;
    updateKeepAlive();
    // Can be disposed whenever now.
  }

  @override
  bool get wantKeepAlive => keepAlive;

  @override
  Widget build(BuildContext context) {
    return Container();
  }
}
    回复于
  • 0

    每次运行 pageChooser 时，不是返回新实例，而是创建一个实例并返回相同的实例 .

    例：

    class Pages extends StatefulWidget {
  @override
  createState() => new PagesState();
}

class PagesState extends State<Pages> {
  int pageIndex = 0;

  // Create all the pages once and return same instance when required
  final ProfilePage _profilePage = new ProfilePage(); 
  final PlanPage _planPage = new PlanPage();
  final StartUpNamerPage _startUpNamerPage = new StartUpNamerPage();


  Widget pageChooser() {
    switch (this.pageIndex) {
      case 0:
        return _profilePage;
        break;

      case 1:
        return _planPage;
        break;

      case 2:
        return _startUpNamerPage;
        break;

      default:
        return new Container(
          child: new Center(
              child: new Text(
                  'No page found by page chooser.',
                  style: new TextStyle(fontSize: 30.0)
              )
          ),
        );
    }
  }

  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
        home: new Scaffold(
            body: pageChooser(),
            bottomNavigationBar: new BottomNavigationBar(
              currentIndex: pageIndex,
              onTap: (int tappedIndex) { //Toggle pageChooser and rebuild state with the index that was tapped in bottom navbar
                setState(
                        (){ this.pageIndex = tappedIndex; }
                );
              },
              items: <BottomNavigationBarItem>[
                new BottomNavigationBarItem(
                    title: new Text('Profile'),
                    icon: new Icon(Icons.account_box)
                ),
                new BottomNavigationBarItem(
                    title: new Text('Plan'),
                    icon: new Icon(Icons.calendar_today)
                ),
                new BottomNavigationBarItem(
                    title: new Text('Startup'),
                    icon: new Icon(Icons.alarm_on)
                )
              ],
            )
        )
    );
  }
}

    或者您可以使用像PageView或Stack这样的小部件来实现相同的功能 .

    希望有所帮助！

    回复于

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