Firebase 颤振-NoSuchMethodError：方法'；[]和#x27；被调用为空

我在尝试使用FutureBuilder从Firestore获取数据时遇到错误。如果用户登录并打印（snapshot.data），我将从firestore中获取正确的快照：

flutter: FirebaseUser({displayName: null, providerId: Firebase, uid: UFubdB2xPCTUu8ESgQikOr9WOe52, phoneNumber: null, isEmailVerified: false, providerData: [{email: titi@momo.com, providerId: password, photoUrl: null, displayName: null, uid: titi@momo.com, phoneNumber: null}], email: titi@momo.com, photoUrl: null, lastSignInTimestamp: 1576367769805, isAnonymous: false, creationTimestamp: 1576367424402})

但是，如果导航到提要屏幕，则在打印时会引发异常（snapshot.data['email']）

主页导航

class MyApp extends StatelessWidget {
  Widget _getScreenId() {
    return StreamBuilder<FirebaseUser>(
        stream: FirebaseAuth.instance.onAuthStateChanged,
        builder: (BuildContext context, snapshot) {
          if (snapshot.hasData) {
            print(snapshot.data);
            return Landing(userId: snapshot.data.uid);
          } else {
            return Login();
          }
        });
  }

用户模型

User(
      {this.id,
      this.email,
      this.password,
      this.fullname,
      this.username,
      this.mobile,
      this.profileImgUrl,
      this.bio});

  factory User.fromDoc(DocumentSnapshot doc) {
    return User(
      id: doc.documentID,
      email: doc['email'],
      fullname: doc['fullname'],
      username: doc['username'],
      mobile: doc['mobile'],
      profileImgUrl: doc['profileImgUrl'],
      bio: doc['bio'] ?? ''
    );
  }

---

我已经尝试了几个选项，希望能得到一些帮助。期货并不总是准备好的，它们是异步的。我想至少插入一个空检查，但这里有一个更好的方法。最好检查

未来

的

连接状态

，检查它是否准备就绪，然后检查数据是否为空。使用

ConnectionState

的另一个好处是能够检查它是否正在等待。然后，您可以显示加载图标或其他内容

class _FeedState extends State<Feed> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Colors.white,
        elevation: 1,
        title: Text('feed screen'),
      ),
      backgroundColor: Colors.white,
      body: FutureBuilder(
        future: usersRef.document(widget.userId).get(),
        builder: (BuildContext context, AsyncSnapshot snapshot) {
          if (snapshot.connectionState == ConnectionState.done) {
            if (snapshot.hasData) {
              print(snapshot.data['email']);
              return Padding(
                padding: const EdgeInsets.only(top: 70, left: 20, right: 20),
                child: Column(
                  children: <Widget>[
                    Text('MeandYou')
                  ],
                ),
              );
            }
          }
        },
      ),
    );
  }
}

class\u FeedState扩展状态{
@凌驾
小部件构建（构建上下文）{
返回脚手架(
appBar:appBar(
背景颜色：Colors.white，
立面图：1，
标题：文本（“提要屏幕”），
),
背景颜色：Colors.white，
正文：未来建设者(
future:usersRef.document（widget.userId）.get（），
生成器：（BuildContext上下文，异步快照）{
if（snapshot.connectionState==connectionState.done）{
if（snapshot.hasData）{
打印（快照数据['email']）；
返回填充(
填充：仅限常量边集（顶部：70，左侧：20，右侧：20），
子：列(
儿童：[
文本（'MeandYou'）
],
),
);
}
}
},
),
);
}
}

我尝试了此操作，但仍然出现错误<代码>颤振：类“DocumentSnapshot”没有实例获取程序“isNotEmpty”。flatter:Receiver:DocumentSnapshot的实例flatter:trusted calling:isNotEmptyWhoops实际上是snapshot.hasdata更好的方法是为类使用流和业务逻辑代码。流监视事件并处理这些事件，然后返回数据。这是Marcus Ng的教程吗？我也有同样的问题…@小朝阳是的。请检查下面的解决方案。

children: <Widget>[
          Home(),
          Feed(userId: widget.userId),
          Profile(),
        ],

class Feed extends StatefulWidget {
  final String userId;

  Feed({this.userId});

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

class _FeedState extends State<Feed> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Colors.white,
        elevation: 1,
        title: Text('feed screen'),
      ),
      backgroundColor: Colors.white,
      body: FutureBuilder(
        future: usersRef.document(widget.userId).get(),
        builder: (BuildContext context, AsyncSnapshot snapshot) {
          print(snapshot.data['email']);
          return Padding(
            padding: const EdgeInsets.only(top: 70, left: 20, right: 20),
            child: Column(
              children: <Widget>[
                Text('MeandYou')
              ],
            ),
          );
        },
      ),
    );
  }
}

final usersRef = _firestore.collection('users');

User(
      {this.id,
      this.email,
      this.password,
      this.fullname,
      this.username,
      this.mobile,
      this.profileImgUrl,
      this.bio});

  factory User.fromDoc(DocumentSnapshot doc) {
    return User(
      id: doc.documentID,
      email: doc['email'],
      fullname: doc['fullname'],
      username: doc['username'],
      mobile: doc['mobile'],
      profileImgUrl: doc['profileImgUrl'],
      bio: doc['bio'] ?? ''
    );
  }

class _FeedState extends State<Feed> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Colors.white,
        elevation: 1,
        title: Text('feed screen'),
      ),
      backgroundColor: Colors.white,
      body: FutureBuilder(
        future: usersRef.document(widget.userId).get(),
        builder: (BuildContext context, AsyncSnapshot snapshot) {
          if (snapshot.connectionState == ConnectionState.done) {
            if (snapshot.hasData) {
              print(snapshot.data['email']);
              return Padding(
                padding: const EdgeInsets.only(top: 70, left: 20, right: 20),
                child: Column(
                  children: <Widget>[
                    Text('MeandYou')
                  ],
                ),
              );
            }
          }
        },
      ),
    );
  }
}