snapshot.value []未定义，错误将快照转换为对象

Question

我是新手的颤音，我的模型类方法触点有错误。fromSnapshot我想将Snapsot转换为对象。错误在snapshot.value [];的括号上。这是错误：

未针对类型的“对象”定义运算符'[]'。尝试定义操作员'[]'。

我如何解决此错误？

import 'package:firebase_database/firebase_database.dart';

   class Contact {
    String? _id;
    String? _firstName;
    String? _lastName;
    String? _phone;
    String? _email;
    String? _address;
    String? _photoUrl;

  //Constructor for add

   Contact(this._firstName, this._lastName, this._phone, this._email,
   this._address, this._photoUrl);

 //Constructor for Edit

   Contact.withId(this._id, this._firstName, this._lastName, this._phone,
   this._email, this._address, this._photoUrl);

  //Getters

   String? get id => _id;
   String? get lastName => _lastName;
   String? get firstName => _firstName;
   String? get phone => _phone;
   String? get email => _email;
   String? get address => _address;
   String? get photoUrl => _photoUrl;

   //setters

     set firstName(String? firstname) {
     this._firstName = firstName;
      }

     set lastName(String? lastname) {
     this._lastName = lastName;
      }

     set phone(String? phone) {
     this._phone = phone;
      }

     set email(String? email) {
     this._email = email;
      }

     set address(String? adress) {
     this._address = address;
      }

     set photoUrl(String? photoUrl) {
     this._photoUrl = photoUrl;
      }

 Contact.fromSnapshot(DataSnapshot snapshot) {
    _id = snapshot.key;
    _firstName = snapshot.value!['firstName'];
    _lastName = snapshot.value!['lastName'];
    _phone = snapshot.value!['phone'];
    _email = snapshot.value!['email'];
    _address = snapshot.value!['address'];
    _photoUrl = snapshot.value!['photoUrl'];
 }
}

Answer 1

它不知道snapshot.value是一张地图，因此您需要告诉它。您可以尝试一下：

 Contact.fromSnapshot(DataSnapshot snapshot) {
    Map<dynamic, dynamic> map = snapshot.value! as Map<dynamic, dynamic>;
    _id = snapshot.key;
    _firstName = map['firstName'];
    _lastName = map['lastName'];
    _phone = map['phone'];
    _email = map['email'];
    _address = map['address'];
    _photoUrl = map['photoUrl'];
 }