迁移到 null safety 后无法从 firestore 保存模型中的数据

Question

所以，我有一个用户模型，我想在其中存储 firestore 中存在的文档的值，为此我有以下代码：-

import 'package:cloud_firestore/cloud_firestore.dart';

class UserModel
{
  final String? id;
  final String? username;
  final String? email;
  final String? url;
  final String? androidNotificationToken;

  UserModel({
    this.id,
    this.username,
    this.email,
    this.url,
    this.androidNotificationToken,
  });

  factory UserModel.fromDocument(DocumentSnapshot doc)
  {
    return UserModel(
      id: doc.data()['id'], //error
      username: doc.data()['username'],//error
      email: doc.data()['email'],//error
      url: doc.data()['url'],//error
      androidNotificationToken: doc.data()['androidNotificationToken'],//error
    );
  }
}

我面临的错误是 doc.data() 后的方括号中有一条红线显示错误，如我的代码中所标记。错误是：-

The method '[]' can't be unconditionally invoked because the receiver can be 'null'.

我发现的一个修复方法是将 doc.data()['id'] 替换为 (doc.data() as dynamic)['id]。那么这是最好的方法吗？

Answer 1

你应该替换：

doc.data() as dynamic['id']

与：

doc.data() as Map<String, dynamic>['id']

DocumentSnapshot.data 属于 Map<String, dynamic>.

类型

查看 migration guide cloud_firestore 2.0.0。

迁移到 null safety 后无法从 firestore 保存模型中的数据

Unable to save the data in model from firestore after migrating to null safety

flutter

google-cloud-firestore

dart-null-safety