如何根据flutter中的sharedPrefs值设置动态initialRoute？

Posted 2023-02-23

【中文标题】如何根据flutter中的sharedPrefs值设置动态initialRoute？

【英文标题】：How to set dynamic initialRoute based on sharedPrefs value in flutter?

【发布时间】：2020-03-07 21:10:20

【问题描述】：

目前，我正在处理路线，我想根据 sharedPreferences 值在我的应用中设置 initialRoute。

我在 MaterialAppWidget 中使用 Statedulwidget，并在从 sharedPrefs 获取数据后使用 setState() 方法。但是，每次我得到相同的屏幕。

class MyApp extends StatefulWidget 
  @override
  _MyAppState createState() => _MyAppState();


class _MyAppState extends State<MyApp> 
  int initScreen = 0;

  initPrefs() async 
    SharedPreferences prefs = await SharedPreferences.getInstance();
    initScreen = prefs.getInt("initScreen");

    print("initScreen $initScreen");
    setState(() );
  

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

    initPrefs();
  

  @override
  Widget build(BuildContext context) 
    print("initScreen2 $initScreen");
    return MaterialApp(
        debugShowCheckedModeBanner: false,
        title: 'Flutter Authentication',
        theme: ThemeData(
          primarySwatch: Colors.blue,
        ),
        initialRoute: initScreen == 0 || initScreen == null
            ? MediatorPage.routeName
            : PopUntilPage.routeName,
        routes: 
          CloudGroupCreate.routeName: (context) => CloudGroupCreate(),
          CloudDashboard.routeName: (context) => CloudDashboard(),
          PopUntilPage.routeName: (context) => PopUntilPage(),
          ProviderWithFutureBuilderApp.routeName: (context) =>
              ProviderWithFutureBuilderApp(),
          MediatorPage.routeName: (context) => MediatorPage(),
        ,
        );
  

我不想通过家庭财产应用程序使用直接小部件。我只想浏览并且仅使用命名路线。

谁能建议如何正确地做到这一点？

谢谢。

【参考方案1】：

你需要在main()中初始化SharedPreferences并使用WidgetsFlutterBinding.ensureInitialized 您可以在下面复制粘贴运行完整代码 在演示中，我将 initScreen 设置为 12

代码sn-p

int initScreen;

Future<void> main() async 
  WidgetsFlutterBinding.ensureInitialized();
  SharedPreferences prefs = await SharedPreferences.getInstance();
  await prefs.setInt("initScreen",12);
  initScreen = await prefs.getInt("initScreen");
  print('initScreen $initScreen');
  runApp(MyApp());


...
initialRoute: initScreen == 0 || initScreen == null
          ? "/"
          : "first",
      routes: 
        '/': (context) => MyHomePage(title: "demo",),
        "first": (context) => FirstPage(),
      ,

工作演示

完整代码

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

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

int initScreen;

Future<void> main() async 
  WidgetsFlutterBinding.ensureInitialized();
  SharedPreferences prefs = await SharedPreferences.getInstance();
  await prefs.setInt("initScreen",12);
  initScreen = await prefs.getInt("initScreen");
  print('initScreen $initScreen');
  runApp(MyApp());


class MyApp extends StatelessWidget 
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) 
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
      ),
      initialRoute: initScreen == 0 || initScreen == null
          ? "/"
          : "first",
      routes: 
        '/': (context) => MyHomePage(title: "demo",),
        "first": (context) => FirstPage(),
      ,
      //home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  


class MyHomePage extends StatefulWidget 
  MyHomePage(Key key, this.title) : super(key: key);

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

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


class _MyHomePageState extends State<MyHomePage> 
  int _counter = 0;

  void _incrementCounter() 
    setState(() 
      // This call to setState tells the Flutter framework that something has
      // changed in this State, which causes it to rerun the build method below
      // so that the display can reflect the updated values. If we changed
      // _counter without calling setState(), then the build method would not be
      // called again, and so nothing would appear to happen.
      _counter++;
    );
  

  @override
  Widget build(BuildContext context) 
    // This method is rerun every time setState is called, for instance as done
    // by the _incrementCounter method above.
    //
    // The Flutter framework has been optimized to make rerunning build methods
    // fast, so that you can just rebuild anything that needs updating rather
    // than having to individually change instances of widgets.
    return Scaffold(
      appBar: AppBar(
        // Here we take the value from the MyHomePage object that was created by
        // the App.build method, and use it to set our appbar title.
        title: Text(widget.title),
      ),
      body: Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: Column(
          // Column is also a layout widget. It takes a list of children and
          // arranges them vertically. By default, it sizes itself to fit its
          // children horizontally, and tries to be as tall as its parent.
          //
          // Invoke "debug painting" (press "p" in the console, choose the
          // "Toggle Debug Paint" action from the Flutter Inspector in android
          // Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
          // to see the wireframe for each widget.
          //
          // Column has various properties to control how it sizes itself and
          // how it positions its children. Here we use mainAxisAlignment to
          // center the children vertically; the main axis here is the vertical
          // axis because Columns are vertical (the cross axis would be
          // horizontal).
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.display1,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  


class FirstPage extends StatelessWidget 
  @override
  Widget build(BuildContext context) 
    return Text("First");
  

【参考方案2】：

一个简单的方法是在加载完成后使用一个标志，然后在构建中：

return _isLoadComplete? MaterialApp() : Container();

另一个选项，似乎 MaterialApp 正在被缓存，并且 initialRoute 没有第二次运行。使用密钥似乎可以解决此问题：

return MaterialApp(
      key: UniqueKey(),
//etc

我倾向于第一种方法，因为没有必要让 MaterialApp 尝试显示一个视图，会立即用另一个视图替换它。