“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

根据Net Ninja在youtube上的教程，我正在学习在扑朔迷离中使用Firestore。在完成用户身份验证之后，只要创建新用户，此人便将用户记录添加到数据库中，为此，通过传递1个名为 name的字符串来添加新模型。从我对调用的理解中，他映射了模型，然后使用.data ['name']从模型中获取该字符串（字符串称为name），并且在执行此操作时，出现错误没有为类型 Map< String，dynamic>定义运算符 [] Function（）'为什么会出现此错误？

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（以下代码包装在名为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

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;
    }
  }

如果您有任何疑问或需要查看更多代码，请让我在评论中知道

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

推荐答案

更改此内容：

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

到此：

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

data（）是一种方法，因此您现在有了从源代码添加（）：

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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