flutter - 在 Dart 中克服运算符(operator)分配的最简单方法

Question

我正在开发一个flutter应用程序。当我使用DocumentSnapshot时，我的flutter项目在工厂构造函数中显示错误
User.dart

import 'package:cloud_firestore/cloud_firestore.dart';

class User {
  final String id;
  final String username;
  final String email;
  final String photoUrl;
  final String displayname;
  final String bio;

  User({
   this.id,
   this.username,
   this.email,
   this.photoUrl,
   this.displayname,
   this.bio
  });

  factory User.fromDoc(DocumentSnapshot doc){
    return User(
      id: doc['id'],
      username: doc['username'],
      email: doc['email'],
      photoUrl: doc['photoUrl'],
      displayname: doc['displayName'],
      bio: doc['bio'],
    );
  }
}

错误记录

Launching lib\main.dart on sdk gphone x86 arm in debug mode...
Running Gradle task 'assembleDebug'...
lib/models/user.dart:22:14: Error: The operator '[]' isn't defined for the class 'DocumentSnapshot'.
 - 'DocumentSnapshot' is from 'package:cloud_firestore/cloud_firestore.dart' ('/C:/flutter/flutter/.pub-cache/hosted/pub.dartlang.org/cloud_firestore-0.14.0+2/lib/cloud_firestore.dart').
Try correcting the operator to an existing operator, or defining a '[]' operator.
      id: doc['id'],
             ^
lib/models/user.dart:23:20: Error: The operator '[]' isn't defined for the class 'DocumentSnapshot'.
 - 'DocumentSnapshot' is from 'package:cloud_firestore/cloud_firestore.dart' ('/C:/flutter/flutter/.pub-cache/hosted/pub.dartlang.org/cloud_firestore-0.14.0+2/lib/cloud_firestore.dart').
Try correcting the operator to an existing operator, or defining a '[]' operator.
      username: doc['username'],
                   ^
lib/models/user.dart:24:17: Error: The operator '[]' isn't defined for the class 'DocumentSnapshot'.
 - 'DocumentSnapshot' is from 'package:cloud_firestore/cloud_firestore.dart' ('/C:/flutter/flutter/.pub-cache/hosted/pub.dartlang.org/cloud_firestore-0.14.0+2/lib/cloud_firestore.dart').
Try correcting the operator to an existing operator, or defining a '[]' operator.
      email: doc['email'],
                ^
lib/models/user.dart:25:20: Error: The operator '[]' isn't defined for the class 'DocumentSnapshot'.
 - 'DocumentSnapshot' is from 'package:cloud_firestore/cloud_firestore.dart' ('/C:/flutter/flutter/.pub-cache/hosted/pub.dartlang.org/cloud_firestore-0.14.0+2/lib/cloud_firestore.dart').
Try correcting the operator to an existing operator, or defining a '[]' operator.
      photoUrl: doc['photoUrl'],
                   ^
lib/models/user.dart:26:23: Error: The operator '[]' isn't defined for the class 'DocumentSnapshot'.
 - 'DocumentSnapshot' is from 'package:cloud_firestore/cloud_firestore.dart' ('/C:/flutter/flutter/.pub-cache/hosted/pub.dartlang.org/cloud_firestore-0.14.0+2/lib/cloud_firestore.dart').
Try correcting the operator to an existing operator, or defining a '[]' operator.
      displayname: doc['displayName'],
                      ^
lib/models/user.dart:27:15: Error: The operator '[]' isn't defined for the class 'DocumentSnapshot'.
 - 'DocumentSnapshot' is from 'package:cloud_firestore/cloud_firestore.dart' ('/C:/flutter/flutter/.pub-cache/hosted/pub.dartlang.org/cloud_firestore-0.14.0+2/lib/cloud_firestore.dart').
Try correcting the operator to an existing operator, or defining a '[]' operator.
      bio: doc['bio'],
              ^


FAILURE: Build failed with an exception.

* Where:
Script 'C:\flutter\flutter\packages\flutter_tools\gradle\flutter.gradle' line: 896

* What went wrong:
Execution failed for task ':app:compileFlutterBuildDebug'.
> Process 'command 'C:\flutter\flutter\bin\flutter.bat'' finished with non-zero exit value 1

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 7s
Exception: Gradle task assembleDebug failed with exit code 1

因为我必须在应用程序的各个部分中使用DocumentSnapshot，所以有什么方法可以纠正此运算符(operator)问题吗？是否有可用的永久解决方案来使用这种方法？
谢谢

Answer 1

如果要访问Firebase DocumentSnapshot，则需要访问其数据属性snapshot.data。如果要访问其后面的 map ，请使用snapshot.data.data因此，在您的示例中，如下所示:

  factory User.fromDoc(DocumentSnapshot doc){
    return User(
      id: doc.data.data['id'],
      username: doc.data.data['username'],
      email: doc.data.data['email'],
      photoUrl: doc.data.data['photoUrl'],
      displayname: doc.data.data['displayName'],
      bio: doc.data.data['bio'],
    );
  }
}

请参阅官方文档中的 One-Time Read部分:
https://firebase.flutter.dev/docs/firestore/usage/