I have following model class.

@JsonSerializable()
class Login {
  String? userName;
  String? password;

  Login({required this.userName, required this.password});

  factory Login.fromJson(Map<String, dynamic> json) => _$LoginFromJson(json);
  Map<String, dynamic> toJson() => _$LoginToJson(this);
}

Generated part file.

Login _$LoginFromJson(Map<String, dynamic> json) => Login(
      userName: json['userName'] as String?,
      password: json['password'] as String?,
    );

Map<String, dynamic> _$LoginToJson(Login instance) => <String, dynamic>{
      'userName': instance.userName,
      'password': instance.password,
    };

when i try to use it to post to api with follow code

  Future<void> loginUser(Login login) async => {
        print(login.toJson().toString());
}

Result from the print statement (cause convertion error)

{userName: test, password: password}

Expecting valid json to post is

{
  "username": "string",
  "password": "string"
}

Error Message

Error: DioError [DioErrorType.other]: Converting object to an encodable object failed: Instance of '_HashSet<String>'

CodePudding user response：

Remove the => from

Future<void> loginUser(Login login) async => {
  print(login.toJson().toString());
}

to

Future<void> loginUser(Login login) async {
  print(login.toJson().toString());
}

In the first example, it is an arrow function where the brackets { } stand for a set literal since it's right after the arrow, much like in the generated _$LoginToJson function but without describing the types of the set.

In the second example, it is a normal function the brackets { } define the body of the function.

You might be looking to call jsonEncode (import dart:convert;) which takes a value, such as a Map<String, dynamic> and turns it into a String in json format.

Update the print statement as follows:

print(jsonEncode(login.toJson()));

While the generated functions parse the object to a format that is suitable for JSON, it doesn't turn it into an actual String. You'll need to encode it with jsonEncode. Similarly, when processing a JSON response, you'll need to jsonDecode the response body to get a Map<String, dynamic> structure that you can then pass into the generated fromJson functions.