“未定义运算符‘[]’"；在 flutter firestore 中使用 .data[] 时出错 [英] "The operator '[]' isn't defined" error when using .data[] in flutter firestore

问题描述

我正在按照 youtube 上的 Net Ninja 教程学习在 flutter 中使用 firestore.完成用户身份验证后，每当创建新用户时，这个人都会将用户记录添加到数据库中，为此，添加了一个新模型，传递 1 个名为name"的字符串.根据我对调用他映射模型的理解，然后使用 .data['name'] 从模型中获取该字符串(字符串被称为 name)，在执行此操作时，我收到错误 The operator '[]' 没有为类型 'Map 定义.Function()' 为什么我会收到这个错误?

I am learning to use firestore in flutter following Net Ninja's tutorial on youtube. After user authenticatin was done this guy added user records to the database whenever a new user is created, for doing this a new model was added passing 1 String named "name" and from what I undertstood for calling that he mapped the model and then used .data['name'] to get that string from the model(string was called name) and when doing this, I got the error The operator '[]' isn't defined for the type 'Map<String, dynamic> Function()' Why am I getting this error?

用户名模型

class Username {
  final String name;
  Username({ this.name });
}

databse.dart 文件(以下代码封装在一个名为 DatabaseService 的类中)

databse.dart file (the following code is wrapped in a class called DatabaseService)

  List<Username> _usernameListFromSnapshot(QuerySnapshot snapshot) {
    return snapshot.docs.map((doc){
      return Username(
        name: doc.data['name'] ?? '',
      );
    }).toList();
  }

auth.dart

  Future registerWithEmailAndPassword(String email, String password) async {
    try {
      UserCredential result = await _auth.createUserWithEmailAndPassword(email: email, password: password);
      User user = result.user;

      // create a new document for the user with uid
      await DatabaseService(uid: user.uid).updateUserData('user123');
      return _userFromFirebaseUser(user);
    } catch(e) {
      print(e.toString());
      return null;
    }
  }

如果您有任何问题或需要查看更多代码，请在评论中告诉我

if you have any questions or need to see more code, please let me know in the comments

推荐答案

改变这个:

name: doc.data['name'] ?? '' 

进入这个:

name: doc.data()['name'] ?? '' 

data() 现在是一种方法，因此您必须从源代码中添加 () :

data() is a method now therefore you have to add (), from the source code:

  Map<String, dynamic> data() {
    return _CodecUtility.replaceDelegatesWithValueInMap(
        _delegate.data(), _firestore);
  }

https://github.com/FirebaseExtended/flutterfire/blob/master/packages/cloud_firestore/cloud_firestore/lib/src/document_snapshot.dart#L38

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