android - 抖动错误 LateInitializationError : Field '@' has not been initialized

Question

这是预计会导致错误的主程序的中间部分。如果您未在启动屏幕上登录，此代码将转到 MyHomePage 并登录。如果您已登录，它将转到 MainScreen 并切换到应用程序的主屏幕。

  class SplashScreen extends StatefulWidget {
      @override
      _SplashScreenState createState() => _SplashScreenState();
    }
    
    class _SplashScreenState extends State<SplashScreen> {
    
      final FirebaseAuth auth = FirebaseAuth.instance;
      final User? user = FirebaseAuth.instance.currentUser;
    
      @override
      void initState() {
        super.initState();
        _initUser().whenComplete((){
          setState(() {});
        });
      }
    
      _initUser() async {
        if (auth.currentUser != null) {
          Timer(
            Duration(seconds: 2),
                () => Navigator.of(context).pushAndRemoveUntil(
                    MaterialPageRoute(
                        builder: (context) =>
                            MainScreen(user!)),
                        (Route<dynamic> route) => false),
          );
        } else {
          Timer(Duration(seconds: 1),
                  () => Navigator.of(context).pushAndRemoveUntil(
                      MaterialPageRoute(
                          builder: (context) =>
                              MyHomePage()),
                          (Route<dynamic> route) => false),
          );
        }
      }
    
      @override
      Widget build(BuildContext context) {
    
        return Scaffold(
            body: Center(
              child: Text("Splash Screen"),
            ),
    
        );
      }
    }

这是您未登录时传递的 MyHomePage 小部件。

class MyHomePage extends StatefulWidget {
      const MyHomePage({Key? key}) : super(key: key);
    
      @override
      State<MyHomePage> createState() => _MyHomePageState();
    }
    
    class _MyHomePageState extends State<MyHomePage> {
    
      @override
      Widget build(BuildContext context) {
        return Scaffold(
          body: Center(
            child: TextButton(
              onPressed: (){
    
                FirebaseService().signup(context);
              },
              child: Text('Google'),
            ),
          )
        );
      }
    }
    class FirebaseService{
    
      final FirebaseAuth auth = FirebaseAuth.instance;
      final GoogleSignIn googleSignIn = GoogleSignIn();
    
      Future<void> signup(BuildContext context) async {
    
    
      final GoogleSignInAccount? googleSignInAccount = await googleSignIn.signIn();
      if (googleSignInAccount != null) {
        final GoogleSignInAuthentication googleSignInAuthentication =
        await googleSignInAccount.authentication;
        final AuthCredential authCredential = GoogleAuthProvider.credential(
            idToken: googleSignInAuthentication.idToken,
            accessToken: googleSignInAuthentication.accessToken);
    
        // Getting users credential
        UserCredential result = await auth.signInWithCredential(authCredential);
        User? user = result.user;
    
    
        if (user != null) {
          Navigator.push(
              context, MaterialPageRoute(builder: (context) => MainScreen(user)));
        }  // if result not null we simply call the MaterialpageRoute,
        // for go to the HomePage screen
      }
    }
    
      Future<void> signOutFromGoogle() async{
        await googleSignIn.signOut();
        await auth.signOut();
      }
    }

这是错误的内容

The following LateError was thrown building MainScreen(dirty, dependencies: [_InheritedProviderScope<Pro?>], state: _MainScreenState#d95a0):
LateInitializationError: Field '_instance@640075166' has not been initialized.

The relevant error-causing widget was: 
  MainScreen MainScreen:file:///F:/flutter%20project/good_man/lib/main.dart:75:25
When the exception was thrown, this was the stack: 

抱歉，我忘记了主屏幕代码。下面是主屏代码

class MainScreen extends StatefulWidget {
  const MainScreen(this.user);

  final User user;

  @override

  _MainScreenState createState() => _MainScreenState();
}
class _MainScreenState extends State<MainScreen> {
  @override
  Widget build(BuildContext context) {

    final User user = widget.user;
    final pro = Provider.of<Pro>(context);
    return DefaultTabController(
      length: 3,
      child: Scaffold(

          appBar: PreferredSize(
              preferredSize: Size.fromHeight(60.0), // here the desired height
              child: AppBar(
                iconTheme: IconThemeData(color: Colors.black),
                backgroundColor: pro.backColor_main,
                elevation: 0.0,
                centerTitle: true,
                title: Text('aaa',
                  style: TextStyle(
                      fontFamily: 'Gugi',
                      fontSize: 20.sp,
                      color: Colors.black,
                  ),),
              ),
          ),
          drawer: Drawer(
            child: ListView(
              padding: EdgeInsets.zero,
              children: [
                DrawerHeader(
                  child: Text('Drawer Header'),
                  decoration: BoxDecoration(
                    color: Colors.white
                  ),
                ),
                ListTile(
                  title: Text('aaa'),
                  onTap: () {
                    Navigator.pop(context);
                  },
                ),

              ],
            ),
          ),
          bottomNavigationBar: BottomBar(),
          body: Stack(children:  [

            TabBarView(
              children:  [
                MainTest(),
                Text(''),
                Main_User(user),
              ],
            ),
          ])),
    );
  }
}

很抱歉发布所有代码。没有使用 Late 的部分，但错误代码显示为 Late，我尝试删除缓存并启动

Answer 1

实际上错误是在当前用户的初始化中......您必须了解有状态小部件的生命周期......initState 没有保持流量。它只是初始化一些实例值...并且您尝试延迟 2 秒...所以这就是问题所在。

使用 FutureBuilder 进行_initUser()，当它获取所有数据时，然后继续下一个屏幕。