Snapshot.vlaue[ ] are not defined, Error converting snapshot to object - flutter

Question

I am new to flutter, I have Error in my model class Method Contact.fromSnapshot in which i want to convert snapsot to object. Error is on the brackets of snapshot.value[];. This is error:
The operator '[]' isn't defined for the type 'Object'. Try defining the operator '[]'.
How i can fix this error?
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

It doesn't know snapshot.value is a map, so you need to tell it. You could try this:
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'];
}