How to keep the widget's state in Scaffold.drawer in Flutter?

问题

I want to keep the widget's state in Scaffold.drawer. The Scaffold.drawer is a custom widget, which has a RaiseButton in it. When click the button, the text in the button changed. But when the drawer is closed, and reopen the drawer, the changed text is reseted.

I have use " with AutomaticKeepAliveClientMixin<> " in my custom Drawer, but it does't work.

import 'package:flutter/material.dart';

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

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

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key}) : super(key: key);

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Flutter Demo"),
      ),
      drawer: Drawer(child: CustomDrawer(),),
      body: Center(
        child: Text("Flutter Demo"),
      ),
    );
  }
}

class CustomDrawer extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return _CustomDrawerState();
  }
}

class _CustomDrawerState extends State<CustomDrawer> with AutomaticKeepAliveClientMixin<CustomDrawer> {

  String btnText = "Click!";

  @override
  bool get wantKeepAlive => true;

  @override
  Widget build(BuildContext context) {
    super.build(context);
    return Center(
      child: RaisedButton(onPressed: () {
        setState(() {
          btnText = "Clicked!!";
        });
      }, child: Text(btnText),),
    );
  }

}

I expect the widget's state can keep, even if the Drawer is closed.

回答1:

In your case, you have 2 choices:

1. You should keep your state in your Top level widget. in your case _MyHomePageState;
2. Use state managers like Redux, Bloc, ScopedModel. I think ScopedModel is great for you in this case.

otherwise, you can't control the state of Drawer. cause it re-creates every moment you call the Drawer by the action button in Appbar;

回答2:

Create a separate widget for the drawer and just use in anywhere you need to.

Manage the Drawer State with a Provider

class DrawerStateInfo with ChangeNotifier {
  int _currentDrawer = 0;
  int get getCurrentDrawer => _currentDrawer;

  void setCurrentDrawer(int drawer) {
    _currentDrawer = drawer;
    notifyListeners();
  }

  void increment() {
    notifyListeners();
  }
}

Adding State Management to the Widget tree

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MultiProvider(
      child: MaterialApp(
        title: 'Flutter Demo',
        theme: ThemeData(
          primarySwatch: Colors.teal,
        ),
        home: MyHomePage(title: 'Flutter Demo Home Page'),
      ),
      providers: <SingleChildCloneableWidget>[
        ChangeNotifierProvider<DrawerStateInfo>(
            builder: (_) => DrawerStateInfo()),
      ],
    );
  }
}

Creating The Drawer Widget for reuse in application

class MyDrawer extends StatelessWidget {
  MyDrawer(this.currentPage);

  final String currentPage;

  @override
  Widget build(BuildContext context) {
    var currentDrawer = Provider.of<DrawerStateInfo>(context).getCurrentDrawer;
    return Drawer(
      child: ListView(
        children: <Widget>[
          ListTile(
            title: Text(
              "Home",
              style: currentDrawer == 0
                  ? TextStyle(fontWeight: FontWeight.bold)
                  : TextStyle(fontWeight: FontWeight.normal),
            ),
            trailing: Icon(Icons.arrow_forward),
            onTap: () {
              Navigator.of(context).pop();
              if (this.currentPage == "Home") return;

              Provider.of<DrawerStateInfo>(context).setCurrentDrawer(0);

              Navigator.of(context).pushReplacement(MaterialPageRoute(
                  builder: (BuildContext context) =>
                      MyHomePage(title: "Home")));
            },
          ),
          ListTile(
            title: Text(
              "About",
              style: currentDrawer == 1
                  ? TextStyle(fontWeight: FontWeight.bold)
                  : TextStyle(fontWeight: FontWeight.normal),
            ),
            trailing: Icon(Icons.arrow_forward),
            onTap: () {
              Navigator.of(context).pop();
              if (this.currentPage == "About") return;

              Provider.of<DrawerStateInfo>(context).setCurrentDrawer(1);

              Navigator.of(context).pushReplacement(MaterialPageRoute(
                  builder: (BuildContext context) => MyAboutPage()));
            },
          ),
        ],
      ),
    );
  }
}

Use of Drawer in one of your pages

class MyAboutPage extends StatefulWidget {
  @override
  _MyAboutPageState createState() => _MyAboutPageState();
}

class _MyAboutPageState extends State<MyAboutPage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('About Page'),
      ),
      drawer: MyDrawer("About"),
    );
  }
}

来源：https://stackoverflow.com/questions/56735073/how-to-keep-the-widgets-state-in-scaffold-drawer-in-flutter