firebase - 当前用户 Flutter Firebase 出错，如何解决？

Question

当我从显示用户已加载的内容重新启动时，但是当我更改用户时，当我注销并输入另一个用户并进入创建帖子屏幕时，我收到此错误：

════════ Exception caught by widgets library ═══════════════════════════════════
The method '[]' was called on null.
Receiver: null

Tried calling: []("email")
The relevant error-causing widget was
StreamBuilder<DocumentSnapshot<Map<String, dynamic>>>

这没有任何意义，因为正在加载电子邮件，以至于您正在登录并且它在firestore中。这是加载 Circle 头像和名称的 Upload 类中的我的 StreamBuilder。

    final String currentUserId;

  const Upload({Key key, this.currentUserId}) : super(key: key);

StreamBuilder<DocumentSnapshot<Map<String, dynamic>>>(
                stream: usersRef.doc(widget.currentUserId).snapshots(),
                builder: (context,
                    AsyncSnapshot<DocumentSnapshot<Map<String, dynamic>>>
                        snapshot) {
                  if (!snapshot.hasData) {
                    return Center(
                      child: CircularProgressIndicator(
                        valueColor: AlwaysStoppedAnimation(Colors.blue),
                      ),
                    );
                  }
                  UserModel userModel = UserModel.fromDoc(snapshot.data);

                  return Container(
                    child: SizedBox(
                      height: 100,
                      child: ListView(
                        children: [
                          Container(
                              padding: EdgeInsets.symmetric(horizontal: 20),
                              child: Column(
                                crossAxisAlignment: CrossAxisAlignment.start,
                                children: [
                                  Row(
                                    children: [
                                      CircleAvatar(
                                        radius: 22,
                                        backgroundImage: userModel
                                                .profilePicture.isEmpty
                                            ? AssetImage(
                                                'assets/images/placeholder.png')
                                            : NetworkImage(
                                                userModel.profilePicture),
                                      ),
                                      SizedBox(
                                        width: 10,
                                      ),
                                      Text(
                                        userModel.username,
                                        style: TextStyle(
                                            fontSize: 17,
                                            fontWeight: FontWeight.bold),
                                      ),
                                    ],
                                  ),
                                ],
                              ))
                        ],

这是我的班级之家。

class Home extends StatefulWidget {
  final String currentUserId;

  const Home({Key key, this.currentUserId}) : super(key: key);

@override
  void initState() {
    super.initState();
    pageController = PageController();
  }

  @override
  void dispose() {
    pageController.dispose();
    super.dispose();
  }

  onPageChanged(int pageIndex) {
    setState(() {
      this.pageIndex = pageIndex;
    });
  }

  onTap(int pageIndex) {
    pageController.animateToPage(
      pageIndex,
      duration: Duration(milliseconds: 200),
       curve: Curves.easeInOut
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: PageView(
        children: [
          Timeline(currentUserId: widget.currentUserId),
          ActivityFeed(),
          Upload(currentUserId: widget.currentUserId), 
          Search(),
          Profile(currentUserId: widget.currentUserId),
        ],
        controller: pageController,
        onPageChanged: onPageChanged,
        physics: NeverScrollableScrollPhysics(),
      ),
      bottomNavigationBar: CupertinoTabBar(
        currentIndex: pageIndex,
        onTap: onTap,
        activeColor: Theme.of(context).primaryColor,
        items: [
          BottomNavigationBarItem(
            icon: Icon(Icons.whatshot)),
          BottomNavigationBarItem(
            icon: Icon(Icons.notifications)),
          BottomNavigationBarItem(
            icon: Icon(Icons.camera_alt, size: 35.0,)),
          BottomNavigationBarItem(
            icon: Icon(Icons.search)),
          BottomNavigationBarItem(
            icon: Icon(Icons.account_circle)),
        ],
      ),
    );
  }
}

我的用户模型。

class UserModel {
   String id;
   String username;
   String email;
   String profilePicture;
   String coverImage;
   String bio;
  //  String displayName;

  UserModel({
    this.id,
    this.username,
    this.email,
    this.profilePicture,
    this.coverImage,
    // this.displayName,
    this.bio,
  });

  factory UserModel.fromDoc(DocumentSnapshot<Map<String, dynamic>> doc) {
    return UserModel(
      id: doc.id,
      email: doc.data()['email'],
      username: doc.data()['username'],
      profilePicture: doc.data()['profilePicture'],
      coverImage: doc.data()['coverImage'],
      // displayName: doc.data()['displayName'],
      bio: doc.data()['bio'],
    );
  }
}

我的主要。

    Widget getScreenId() {
    return StreamBuilder<User>(
        stream: FirebaseAuth.instance.authStateChanges(),
        builder: (BuildContext context, AsyncSnapshot<User> snapshot) {
          if (snapshot.hasData) {
            return Home(currentUserId: snapshot.data.uid);
          } else {
            return LoginPage();
          }
        });
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme:
          ThemeData(primarySwatch: Colors.deepOrange, accentColor: Colors.teal),
      debugShowCheckedModeBanner: false,
      home: getScreenId(),
    );
  }
}