Navigator.pushReplacement 提供用于空值的空检查运算符。这次是 - 状态答案

【问题标题】：Navigator.pushReplacement gives Null check operator used on a null value. This time it is - stateNavigator.pushReplacement 提供用于空值的空检查运算符。这次是 - 状态
【发布时间】：2022-01-16 04:56:55
【问题描述】：

Google 登录提供程序类未导航到下一个屏幕。登录用户工作，但用户必须登录然后离开应用程序，然后重新打开。重新打开应用程序后，用户登录正常。

错误日志给出： [ERROR:flutter/lib/ui/ui_dart_state.cc(209)] Unhandled Exception: Null check operator used on a null value E/flutter ( 9884): #0 StatefulElement.state (package:flutter/src/widgets/framework.dart:4789:44) E/flutter ( 9884): #1 Navigator.of (package:flutter/src/widgets/navigator.dart:2730:47) E/flutter ( 9884): #2 GoogleSignInProvider.signInwithGoogle (package:blahblah/google_signin_provider.dart:37:17) E/flutter ( 9884): <asynchronous suspension>

错误指向 Navigator 类中的“状态”。如何设置它，以便应用导航？

class GoogleSignInProvider extends ChangeNotifier {

final FirebaseAuth _auth = FirebaseAuth.instance;
User user = firebaseAuth.currentUser;
final GoogleSignIn _googleSignIn = GoogleSignIn();

 Future<String> signInwithGoogle(BuildContext context) async {

  try {
    final GoogleSignInAccount googleSignInAccount =
    await _googleSignIn.signIn();
    final GoogleSignInAuthentication googleSignInAuthentication =
    await googleSignInAccount.authentication;
    final AuthCredential credential = GoogleAuthProvider.credential(
      accessToken: googleSignInAuthentication.accessToken,
      idToken: googleSignInAuthentication.idToken,
    );
    await _auth.signInWithCredential(credential);
  } on FirebaseAuthException catch (e) {
    print(e.message);
    throw e;
  }

  final User currentUser = FirebaseAuth.instance.currentUser;
  String uid = currentUser.uid;
  if (currentUser != null)
    await usersRef.doc(currentUser.uid).set({'id': uid, 'email': 
 currentUser.email,
      'username': currentUser.displayName, 'photoUrl': 
 currentUser.photoURL,
      'phone': '', 'dob': '', 'sex': ''});

 Navigator.of(context).pushReplacement(
      MaterialPageRoute(builder: (_) => TabScreen()));
  notifyListeners();
return null;
}

Future logout() async {
await _googleSignIn.disconnect();
FirebaseAuth.instance.signOut();
}
}

感谢您的帮助！

【问题讨论】：

标签： flutter state navigator

【解决方案1】：

由于您启用了可靠的 null 安全性，因此您无需对 currentUser 进行 null 检查。

【讨论】：