flutter : SharedPreferences not fetching value at app start

Question

我正在尝试存储一个值，并根据该值导航到 LandinPage 或 HomePage。但是，当我的应用程序加载时，我无法获得 SharedPreferences 值。目前，该值是在单击着陆页中的按钮以及关闭/最小化应用程序时设置的。我什至看不到来自 main.dart 的打印消息，也无法获取值。我究竟做错了什么？

这是我的代码:

import 'package:credit/src/pages/landing.dart';
import 'package:flutter/material.dart';
import 'package:credit/src/pages/credit/home.dart';
import 'package:shared_preferences/shared_preferences.dart';

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

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

  _LoadingPageState createState() => _LoadingPageState();
}

class _LoadingPageState extends State<MyApp> {
  @override
  void initState() {
    super.initState();
    getUserStatus().then((userStatus) {
      if (userStatus == null) {
        Navigator.of(context)
            .push(MaterialPageRoute<Null>(builder: (BuildContext context) {
          return LandingPage();
        }));
      } else {
        Navigator.of(context)
            .push(MaterialPageRoute<Null>(builder: (BuildContext context) {
          return HomePage();
        }));
      }
    });
  }

  @override
  Widget build(BuildContext context) {
    return Container(
        child: Center(
      child: CircularProgressIndicator(),
    ));
  }
}

Future<String> getUserStatus() async {
  SharedPreferences prefs = await SharedPreferences.getInstance();
  String userStatus = prefs.getString('userstatus');
  print("==On Load Check ==");
  print(userStatus);
  return userStatus;
}

Answer 1

您可能需要使用在您的两个页面中的任何一个之前首先加载的“加载页面”:

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

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'An App',
      home: LoadingPage(),
      routes: {
        '/landing': (context) => LandingPage(),
        '/home': (context) => HomePage(),
      }
    );
  }
}


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

  _LoadingPageState createState() => _LoadingPageState();
}

class _LoadingPageState extends State<LoadingPage> {
  @override
  void initState() {
    super.initState();
     loadPage();
  }

  loadPage() {
     getUserStatus().then((userStatus) {
      if (userStatus == null) {
        Navigator.of(context).pushNamed('/landing');
      } else {
        Navigator.of(context).pushNamed('/home');
      }
    });
  }

  @override
  Widget build(BuildContext context) {
    return Container(
        child: Center(
      child: CircularProgressIndicator(),
    ));
  }
}

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

  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  @override
  Widget build(BuildContext context) {
    return Container(
       child: Text('Home Page'),
    );
  }
}

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

  _LandingPageState createState() => _LandingPageState();
}


class _LandingPageState extends State<LandingPage> {

  @override
  void initState() {
    super.initState();
    setUserStatus('done');
  }

  @override
  Widget build(BuildContext context) {
    return Container(
       child: Text('Landing'),
    );
  }
}

Future<String> getUserStatus() async {
  SharedPreferences prefs = await SharedPreferences.getInstance();
  String userStatus = prefs.getString('userStatus');
  print("==On Load Check ==");
  print(userStatus);
  return userStatus;
}

Future<bool> setUserStatus(String userStatus) async{
  SharedPreferences prefs = await SharedPreferences.getInstance();
  prefs.setString('userStatus', userStatus);
  return true;
}