如何确定main.dart文件中的默认导航以及如何根据条件检查更改它？

2 回答

• 1

  使用FutureBuilder更容易 . 这个Widget根据Future的结果构建自己 .

  考虑一下：

  void main() => MyApp();
  
  class MyApp extends StatelessWidget {
     Future<bool> isLoggedIn() async {
       SharedPreferences prefs = await SharedPreferences.getInstance();
       return prefs.getBool("loggedIn");
     }
  
     @override
     Widget build(BuildContext context) {
       return MaterialApp(
         home: FutureBuilder(
           future: isLoggedIn(),
           builder: (BuildContext context, AsyncSnapshot<bool> snapshot) {
             if (snapshot.hasData) {
               return snapshot.data ? Main() : Login();
             }
             return Container(); // noop, this builder is called again when the future completes
           },
         );
       );
     }
  }
  
  class Main extends StatelessWidget { ... }
  class Login extends StatelessWidget { ... }
  

  无需操纵Navigator堆栈 .

  回复于 2024-05-16T14:13:04+08:00
• 0

  checkUserAndNavigate 正在返回一个Future，这就是你得到这个错误的原因 . 您可以使用空白加载屏幕/启动画面来读取首选项并从那里导航到正确的屏幕：

  import 'package:flutter/material.dart';
  import 'dart:async';
  
  void main() => runApp(new MyApp());
  
  class MyApp extends StatelessWidget {
    @override
    Widget build(BuildContext context) {
      return new MaterialApp(
        title: 'Flutter Demo',
        theme: new ThemeData(
          primarySwatch: Colors.blue,
        ),
        home: new SplashScreen(),
        routes: {
          '/main': (context) => MyHomePage(title:'Home Page'),
          '/other': (context) => MyHomePage(title:'Other Page'),
        }
      );
    }
  }
  
  Future<bool> checkUserAndNavigate(BuildContext context) async {
    return false;
  } 
  
  class SplashScreen extends StatelessWidget {
    @override
    Widget build(BuildContext context) {
      checkUserAndNavigate(context).then((res) {
        if (res == true) {
          Navigator.pushNamed(context, '/main');
        } else {
          Navigator.pushNamed(context, '/other');
        }
      });
  
      return new Scaffold(
        body: new Card(
          child: new Center(
            child:
              new Text('Loading.....',
                style: new TextStyle(fontSize: 24.00,
                   fontWeight: FontWeight.bold,
                   color: Colors.indigo)
              ),
            )
          ),
      );
    }
  }
  
  class MyHomePage extends StatefulWidget {
    MyHomePage({Key key, this.title}) : super(key: key);
  
    final String title;
  
    @override
    _MyHomePageState createState() => new _MyHomePageState();
  }
  
  class _MyHomePageState extends State<MyHomePage> {
    int _counter = 0;
  
    void _incrementCounter() {
      setState(() {
        _counter++;
      });
    }
  
    @override
    Widget build(BuildContext context) {
      return new Scaffold(
        appBar: new AppBar(
          title: new Text(widget.title),
        ),
      body: new Center(
        child: new Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            new Text(
              'You have pushed the button this many times:',
            ),
            new Text(
              '$_counter',
              style: Theme.of(context).textTheme.display1,
            ),
          ],
        ),
      ),
      floatingActionButton: new FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: new Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
   }
  
   class OtherPage extends StatefulWidget {
     OtherPage({Key key, this.title}) : super(key: key);
  
     final String title;
  
     @override
     _OtherPageState createState() => new _OtherPageState();
   }
  
   class _OtherPageState extends State<OtherPage> {
     int _counter = 0;
  
     void _incrementCounter() {
       setState(() {
         _counter++;
       });
     }
  
     @override
     Widget build(BuildContext context) {
       return new Scaffold(
         appBar: new AppBar(
            title: new Text(widget.title),
         ),
         body: new Center(
           child: new Column(
             mainAxisAlignment: MainAxisAlignment.center,
             children: <Widget>[
                new Text(
                  'You have pushed the button this many times:',
                ),
                new Text(
                  '$_counter',
                  style: Theme.of(context).textTheme.display1,
                ),
             ],
           ),
         ),
      floatingActionButton: new FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: new Icon(Icons.add),
       ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
  }
  

  更改 checkUserAndNavigate 的返回值，您将看到如何加载不同的屏幕 .

  回复于 2024-05-16T14:13:04+08:00