Null-safety for fromJson like methods - json

Question

I want to define a simple class model UserResponse in Flutter 2.0.5 and build a fromJson method attached to this class to create an instance easily after receiving the data from the backend in json format.
class UserResponse {
String name;
UserResponse ({
required this.name,
});
UserResponse.fromJson(Map<String, dynamic> json) {
name= json['name'].toString();
}
}
The dart compiler however throws an error here:
dart(not_initialized_non_nullable_instance_field)
Furthermore:
Non-nullable instance field 'name' must be initialized.
Try adding an initializer expression, or add a field initializer in this constructor, or mark it 'late'.
If I know that I will only call the fromJson method if I have all the required data, how should I create the new Instance in this method? I don't want to change the name field in the class to late.

Answer 1

Use a factory constructor.
class UserResponse {
final String name;
UserResponse({
required this.name,
});
factory UserResponse.fromJson(Map<String, dynamic> json) {
return UserResponse(name: json['name'].toString());
}
}

Answer 2

For null-safety. You need to be check null right way. And front-end need handle server don't return this key, we need mock data and sure app can't crash.
class UserResponse {
UserResponse({
this.name,
});
final String? name;
factory UserResponse.fromRawJson(String str) =>
UserResponse.fromJson(json.decode(str));
String toRawJson() => json.encode(toJson());
factory UserResponse.fromJson(Map<String, dynamic> json) => UserResponse(
name: json["name"] == null ? null : json["name"].toString(),
);
Map<String, dynamic> toJson() => {
"name": name == null ? null : name,
};
}

Answer 3

According to this very similar question there are mainly to ways:
Use an initializer list for the method
Use a factory method
Thus,
UserResponse.fromJson(Map<String, dynamic> json) :
name= json['name'] as String;
or
factory UserResponse.fromJson(Map<String, dynamic> json) {
return UserResponse(
name: json['name'] as String,
);
}