Flutter Firebase authStateChanges() 與 Provider 和 NullSafety On

Question

我見過很多這樣的問題，但其中大多數已經過時，並且沒有使用空安全。

我正在使用 FirebaseAuth 和提供程序來流式傳輸和更新用戶狀態（他是否登錄）

這段代碼有什么問題？

AuthenticationProvider 類

class AuthenticationProvider {
  final FirebaseAuth _firebaseAuth;
  AuthenticationProvider(this._firebaseAuth);

   Stream<User?> get authState => _firebaseAuth.authStateChanges();
  
}

main.dart

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MultiProvider(
      providers: [
        Provider<AuthenticationProvider>(
          create: (_) => AuthenticationProvider(FirebaseAuth.instance),
        ),
        StreamProvider(
          create: (context) =>
              context.read<AuthenticationProvider>().authState,
          initialData: null,
        ),
      ],
      child: MaterialApp(
        title: 'Flutter Demo',
        
        home: SplashScreen(),
        
      ),
    );
  }
}

SplashScreen() 類

 class SplashScreen extends StatelessWidget {
      @override
      Widget build(BuildContext context) {
        final firebaseUser = context.watch<User>();
    
        if (firebaseUser != null) { // This line warning: The operand can't be null, so the condition is always true. Remove the condition.
          return Dashboard();
        }
        return StartingScreen();
      }
    }

Answer 1

鑒於您從User?流開始User? ：

Stream<User?> get authState => _firebaseAuth.authStateChanges();

我認為watch應該在User? 也。 所以：

final firebaseUser = context.watch<User?>();