NoSuchMethodError：方法“ findAncestorStateOfType”在null上调用

如何解决NoSuchMethodError：方法“ findAncestorStateOfType”在null上调用

我建立了一个简单的登录页面，单击该按钮可打开菜单以选择一个Google帐户，然后导航到应用程序的主页。

单击该按钮，但未弹出登录菜单。它抛出一个错误，说：

E/flutter ( 4974): [ERROR:flutter/lib/ui/ui_dart_state.cc(166)] Unhandled Exception: Navigator operation requested with a context that does not include a Navigator. E/flutter ( 4974): The context used to push or pop routes from the Navigator must be that of a widget that is a descendant of a Navigator widget.

我尝试将新上下文添加到树中，但是随后出现了另一个错误：

E/flutter (22865): [ERROR:flutter/lib/ui/ui_dart_state.cc(166)] Unhandled Exception: NoSuchMethodError: The method 'findAncestorStateOfType' was called on null. E/flutter (22865): Receiver: null E/flutter (22865): Tried calling: findAncestorStateOfType()

我该怎么办？

这是我的代码：

import 'package:flutter/material.dart';
import 'package:sorted/screens/sortedMain.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:google_sign_in/google_sign_in.dart';

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

  @override
  _LoginMainState createState() => _LoginMainState();
}

class _LoginMainState extends State<LoginMain> {
  final GoogleSignIn _googleSignIn = GoogleSignIn();
  final FirebaseAuth _auth = FirebaseAuth.instance;
  FirebaseUser _user;

  bool isUserSignedIn = false;

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

    checkIfUserIsSignedIn();
  }

  void checkIfUserIsSignedIn() async {
    var userSignedIn = await _googleSignIn.isSignedIn();

    setState(() {
      isUserSignedIn = userSignedIn;
    });
  }

  Future<FirebaseUser> _handleSignIn() async {
    FirebaseUser user;
    bool userSignedIn = await _googleSignIn.isSignedIn();

    setState(() {
      isUserSignedIn = userSignedIn;
    });

    if (isUserSignedIn) {
      user = await _auth.currentUser();
    } else {
      final GoogleSignInAccount googleUser = await _googleSignIn.signIn();
      final GoogleSignInAuthentication googleAuth =
          await googleUser.authentication;

      final AuthCredential credential = GoogleAuthProvider.getCredential(
        accessToken: googleAuth.accessToken,idToken: googleAuth.idToken,);

      user = (await _auth.signInWithCredential(credential)).user;
      userSignedIn = await _googleSignIn.isSignedIn();
      setState(() {
        isUserSignedIn = userSignedIn;
      });
    }
    _user = user;
    return user;
  }

  void onGoogleSignIn(BuildContext context) async {
    FirebaseUser user = await _handleSignIn().then((value) => null);
    BuildContext context;
    Navigator.push(
      context,MaterialPageRoute(builder: (context) => SortedMain(_googleSignIn,user)),);

    setState(() {
      isUserSignedIn == null ? true : false;
    });
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: SafeArea(
        child: Scaffold(
          appBar: AppBar(
            title: Text('Sorted.'),backgroundColor: Color(0xff0A3D62),flexibleSpace: Container(
              decoration: BoxDecoration(
                  gradient: LinearGradient(
                      begin: Alignment.topLeft,end: Alignment.bottomRight,colors: <Color>[
                    const Color(0xFF5761B2),const Color(0xFF1FC588),])),),drawer: null,body: Container(
              padding: EdgeInsets.only(top: 30),width: 360,height: 600,color: const Color(0xFF273748),child: Column(
                crossAxisAlignment: CrossAxisAlignment.center,children: [
                  Container(
                      width: 300,height: 300,padding: EdgeInsets.all(15),decoration: BoxDecoration(
                        shape: BoxShape.rectangle,borderRadius: BorderRadius.circular(20.0),gradient: LinearGradient(
                            begin: Alignment.topLeft,colors: [Colors.white,Colors.grey[400]]),child: MaterialButton(
                        height: 50.0,minWidth: 150.0,color: Colors.green,splashColor: Colors.teal,textColor: Colors.white,child: new Icon(Icons.arrow_forward),onPressed: () {
                          BuildContext context;
                          onGoogleSignIn(context);
                        },)),],);
  }
}

解决方法

尝试使用以下代码来设置Firebase类

import 'package:firebase_auth/firebase_auth.dart';
import 'package:google_sign_in/google_sign_in.dart';

class AuthProvider {
  final FirebaseAuth _auth = FirebaseAuth.instance;

  User _userFromFirebaseUser(FirebaseUser user) {
    return user != null ? User(uid: user.uid) : null;
  }


  Future<bool> loginWithGoogle() async {
    try {
      GoogleSignIn googleSignIn = GoogleSignIn();
      GoogleSignInAccount account = await googleSignIn.signIn();
      if (account == null) return false;
      AuthResult res =
          await _auth.signInWithCredential(GoogleAuthProvider.getCredential(
        idToken: (await account.authentication).idToken,accessToken: (await account.authentication).accessToken,));
      if (res.user == null) return false;
      return true;
    } catch (e) {
      print("Error logging with google");
      return false;
    }
  }
  
  Future<void> logOut() async {
    try {
      await _auth.signOut();
    } catch (e) {
      print("error logging out");
    }
  }
}
class User {

  final String uid;

  User({ this.uid });

}

并尝试使用if语句限制您的导航器，以便在未完成登录过程的情况下无法导航。

CustomButtom(
       onpressed :  () async {
              bool res = await AuthProvider().loginWithGoogle();
              if (res) {
                Navigator.push(context,MaterialPageRoute(builder: (context) => SortedMain()));
              } else
                print("Login failed");
            },),

希望有帮助！