使用Google登录后，导航器不会转到下一页

Question

当我按下“使用Google登录”按钮时，它为我提供了要登录的帐户。但是之后，当我选择一个帐户时，它正在加载和加载。它应该导航到另一个页面...但是导航器无法正常工作。

我一直在这样做： https://medium.com/@duytq94/building-a-chat-app-with-flutter-and-firebase-from-scratch-9eaa7f41782e

GitHub链接： https://github.com/duytq94/flutter-chat-demo

1）这是login.dart：

import 'dart:async';

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';

import 'package:fluttertoast/fluttertoast.dart';
import 'package:google_sign_in/google_sign_in.dart';
import 'package:p_chat_2/const.dart';
import 'package:p_chat_2/main.dart';
import 'package:shared_preferences/shared_preferences.dart';

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Chat Demo',
      theme: ThemeData(
        primaryColor: themeColor,
      ),
      home: LoginScreen(title: 'CHAT DEMO'),
      debugShowCheckedModeBanner: false,
    );
  }
}

class LoginScreen extends StatefulWidget {
  LoginScreen({Key key, this.title}) : super(key: key);

  final String title;

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

class LoginScreenState extends State<LoginScreen> {
  final GoogleSignIn googleSignIn = GoogleSignIn();
  final FirebaseAuth firebaseAuth = FirebaseAuth.instance;
  SharedPreferences prefs;

  bool isLoading = false;
  bool isLoggedIn = false;
  FirebaseUser currentUser;

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

  void isSignedIn() async {
    this.setState(() {
      isLoading = true;
    });

    prefs = await SharedPreferences.getInstance();

    isLoggedIn = await googleSignIn.isSignedIn();
    if (isLoggedIn) {
      Navigator.push(
        context,
        MaterialPageRoute(builder: (context) => MainScreen(currentUserId: prefs.getString('id'))),
      );
    }

    this.setState(() {
      isLoading = false;
    });
  }

  Future<Null> handleSignIn() async {
    prefs = await SharedPreferences.getInstance();

    this.setState(() {
      isLoading = true;
    });

    GoogleSignInAccount googleUser = await googleSignIn.signIn();
    GoogleSignInAuthentication googleAuth = await googleUser.authentication;

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

    FirebaseUser firebaseUser = await firebaseAuth.signInWithCredential(credential);

    if (firebaseUser != null) {
      // Check is already sign up
      final QuerySnapshot result =
      await Firestore.instance.collection('users').where('id', isEqualTo: firebaseUser.uid).getDocuments();
      final List<DocumentSnapshot> documents = result.documents;
      if (documents.length == 0) {
        // Update data to server if new user
        Firestore.instance
            .collection('users')
            .document(firebaseUser.uid)
            .setData({'nickname': firebaseUser.displayName, 'photoUrl': firebaseUser.photoUrl, 'id': firebaseUser.uid});

        // Write data to local
        currentUser = firebaseUser;
        await prefs.setString('id', currentUser.uid);
        await prefs.setString('nickname', currentUser.displayName);
        await prefs.setString('photoUrl', currentUser.photoUrl);
      } else {
        // Write data to local
        await prefs.setString('id', documents[0]['id']);
        await prefs.setString('nickname', documents[0]['nickname']);
        await prefs.setString('photoUrl', documents[0]['photoUrl']);
        await prefs.setString('aboutMe', documents[0]['aboutMe']);
      }
      Fluttertoast.showToast(msg: "Sign in success");
      this.setState(() {
        isLoading = false;
      });

      Navigator.push(
        context,
        MaterialPageRoute(
            builder: (context) => MainScreen(
              currentUserId: firebaseUser.uid,
            )),
      );
    } else {
      Fluttertoast.showToast(msg: "Sign in fail");
      this.setState(() {
        isLoading = false;
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text(
            widget.title,
            style: TextStyle(color: primaryColor, fontWeight: FontWeight.bold),
          ),
          centerTitle: true,
        ),
        body: Stack(
          children: <Widget>[
            Center(
              child: FlatButton(
                  onPressed: handleSignIn,
                  child: Text(
                    'SIGN IN WITH GOOGLE',
                    style: TextStyle(fontSize: 16.0),
                  ),
                  color: Color(0xffdd4b39),
                  highlightColor: Color(0xffff7f7f),
                  splashColor: Colors.transparent,
                  textColor: Colors.white,
                  padding: EdgeInsets.fromLTRB(30.0, 15.0, 30.0, 15.0)),
            ),

            // Loading
            Positioned(
              child: isLoading
                  ? Container(
                child: Center(
                  child: CircularProgressIndicator(
                    valueColor: AlwaysStoppedAnimation<Color>(themeColor),
                  ),
                ),
                color: Colors.white.withOpacity(0.8),
              )
                  : Container(),
            ),
          ],
        ));
  }
}

---

2）main.dart

import 'dart:async';
import 'dart:io';

import 'package:cached_network_image/cached_network_image.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';

import 'package:google_sign_in/google_sign_in.dart';
import 'package:p_chat_2/chat.dart';
import 'package:p_chat_2/const.dart';
import 'package:p_chat_2/login.dart';
import 'package:p_chat_2/settings.dart';

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

class MainScreen extends StatefulWidget {
  final String currentUserId;

  MainScreen({Key key, @required this.currentUserId}) : super(key: key);

  @override
  State createState() => MainScreenState(currentUserId: currentUserId);
}

class MainScreenState extends State<MainScreen> {
  MainScreenState({Key key, @required this.currentUserId});

  final String currentUserId;

  bool isLoading = false;
  List<Choice> choices = const <Choice>[
    const Choice(title: 'Settings', icon: Icons.settings),
    const Choice(title: 'Log out', icon: Icons.exit_to_app),
  ];

  Future<bool> onBackPress() {
    openDialog();
    return Future.value(false);
  }

  Future<Null> openDialog() async {
    switch (await showDialog(
        context: context,
        builder: (BuildContext context) {
          return SimpleDialog(
            contentPadding: EdgeInsets.only(left: 0.0, right: 0.0, top: 0.0, bottom: 0.0),
            children: <Widget>[
              Container(
                color: themeColor,
                margin: EdgeInsets.all(0.0),
                padding: EdgeInsets.only(bottom: 10.0, top: 10.0),
                height: 100.0,
                child: Column(
                  children: <Widget>[
                    Container(
                      child: Icon(
                        Icons.exit_to_app,
                        size: 30.0,
                        color: Colors.white,
                      ),
                      margin: EdgeInsets.only(bottom: 10.0),
                    ),
                    Text(
                      'Exit app',
                      style: TextStyle(color: Colors.white, fontSize: 18.0, fontWeight: FontWeight.bold),
                    ),
                    Text(
                      'Are you sure to exit app?',
                      style: TextStyle(color: Colors.white70, fontSize: 14.0),
                    ),
                  ],
                ),
              ),
              SimpleDialogOption(
                onPressed: () {
                  Navigator.pop(context, 0);
                },
                child: Row(
                  children: <Widget>[
                    Container(
                      child: Icon(
                        Icons.cancel,
                        color: primaryColor,
                      ),
                      margin: EdgeInsets.only(right: 10.0),
                    ),
                    Text(
                      'CANCEL',
                      style: TextStyle(color: primaryColor, fontWeight: FontWeight.bold),
                    )
                  ],
                ),
              ),
              SimpleDialogOption(
                onPressed: () {
                  Navigator.pop(context, 1);
                },
                child: Row(
                  children: <Widget>[
                    Container(
                      child: Icon(
                        Icons.check_circle,
                        color: primaryColor,
                      ),
                      margin: EdgeInsets.only(right: 10.0),
                    ),
                    Text(
                      'YES',
                      style: TextStyle(color: primaryColor, fontWeight: FontWeight.bold),
                    )
                  ],
                ),
              ),
            ],
          );
        })) {
      case 0:
        break;
      case 1:
        exit(0);
        break;
    }
  }

  Widget buildItem(BuildContext context, DocumentSnapshot document) {
    if (document['id'] == currentUserId) {
      return Container();
    } else {
      return Container(
        child: FlatButton(
          child: Row(
            children: <Widget>[
              Material(
                child: document['photoUrl'] != null
                    ? CachedNetworkImage(
                  placeholder: (context, url) => Container(
                    child: CircularProgressIndicator(
                      strokeWidth: 1.0,
                      valueColor: AlwaysStoppedAnimation<Color>(themeColor),
                    ),
                    width: 50.0,
                    height: 50.0,
                    padding: EdgeInsets.all(15.0),
                  ),
                  imageUrl: document['photoUrl'],
                  width: 50.0,
                  height: 50.0,
                  fit: BoxFit.cover,
                )
                    : Icon(
                  Icons.account_circle,
                  size: 50.0,
                  color: greyColor,
                ),
                borderRadius: BorderRadius.all(Radius.circular(25.0)),
                clipBehavior: Clip.hardEdge,
              ),
              Flexible(
                child: Container(
                  child: Column(
                    children: <Widget>[
                      Container(
                        child: Text(
                          'Nickname: ${document['nickname']}',
                          style: TextStyle(color: primaryColor),
                        ),
                        alignment: Alignment.centerLeft,
                        margin: EdgeInsets.fromLTRB(10.0, 0.0, 0.0, 5.0),
                      ),
                      Container(
                        child: Text(
                          'About me: ${document['aboutMe'] ?? 'Not available'}',
                          style: TextStyle(color: primaryColor),
                        ),
                        alignment: Alignment.centerLeft,
                        margin: EdgeInsets.fromLTRB(10.0, 0.0, 0.0, 0.0),
                      )
                    ],
                  ),
                  margin: EdgeInsets.only(left: 20.0),
                ),
              ),
            ],
          ),
          onPressed: () {
            Navigator.push(
                context,
                MaterialPageRoute(
                    builder: (context) => Chat(
                      peerId: document.documentID,
                      peerAvatar: document['photoUrl'],
                    )));
          },
          color: greyColor2,
          padding: EdgeInsets.fromLTRB(25.0, 10.0, 25.0, 10.0),
          shape: RoundedRectangleBorder(borderRadius: BorderRadius.circular(10.0)),
        ),
        margin: EdgeInsets.only(bottom: 10.0, left: 5.0, right: 5.0),
      );
    }
  }

  final GoogleSignIn googleSignIn = GoogleSignIn();

  void onItemMenuPress(Choice choice) {
    if (choice.title == 'Log out') {
      handleSignOut();
    } else {
      Navigator.push(context, MaterialPageRoute(builder: (context) => Settings()));
    }
  }

  Future<Null> handleSignOut() async {
    this.setState(() {
      isLoading = true;
    });

    await FirebaseAuth.instance.signOut();
    await googleSignIn.disconnect();
    await googleSignIn.signOut();

    this.setState(() {
      isLoading = false;
    });

    Navigator.of(context)
        .pushAndRemoveUntil(MaterialPageRoute(builder: (context) => MyApp()), (Route<dynamic> route) => false);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(
          'MAIN',
          style: TextStyle(color: primaryColor, fontWeight: FontWeight.bold),
        ),
        centerTitle: true,
        actions: <Widget>[
          PopupMenuButton<Choice>(
            onSelected: onItemMenuPress,
            itemBuilder: (BuildContext context) {
              return choices.map((Choice choice) {
                return PopupMenuItem<Choice>(
                    value: choice,
                    child: Row(
                      children: <Widget>[
                        Icon(
                          choice.icon,
                          color: primaryColor,
                        ),
                        Container(
                          width: 10.0,
                        ),
                        Text(
                          choice.title,
                          style: TextStyle(color: primaryColor),
                        ),
                      ],
                    ));
              }).toList();
            },
          ),
        ],
      ),
      body: WillPopScope(
        child: Stack(
          children: <Widget>[
            // List
            Container(
              child: StreamBuilder(
                stream: Firestore.instance.collection('users').snapshots(),
                builder: (context, snapshot) {
                  if (!snapshot.hasData) {
                    return Center(
                      child: CircularProgressIndicator(
                        valueColor: AlwaysStoppedAnimation<Color>(themeColor),
                      ),
                    );
                  } else {
                    return ListView.builder(
                      padding: EdgeInsets.all(10.0),
                      itemBuilder: (context, index) => buildItem(context, snapshot.data.documents[index]),
                      itemCount: snapshot.data.documents.length,
                    );
                  }
                },
              ),
            ),

            // Loading
            Positioned(
              child: isLoading
                  ? Container(
                child: Center(
                  child: CircularProgressIndicator(valueColor: AlwaysStoppedAnimation<Color>(themeColor)),
                ),
                color: Colors.white.withOpacity(0.8),
              )
                  : Container(),
            )
          ],
        ),
        onWillPop: onBackPress,
      ),
    );
  }
}

class Choice {
  const Choice({this.title, this.icon});

  final String title;
  final IconData icon;
}

---

注意：login.dart应该导航到main.dart，但这没有发生。 谢谢：