Generics in Dart/Flutter

 1. Define the data model class representing your JSON structure. In this case, you have a JSON response with three fields: "status," "message," and "data." The "data" field contains an array of objects having "id" and "name" fields. Here's an example of how you can define the data model:

class ApiResponse<T> { int status; String message; T data; ApiResponse({required this.status, required this.message, required this.data}); factory ApiResponse.fromJson(Map<String, dynamic> json, Function fromJsonT) { return ApiResponse( status: json['status'], message: json['message'], data: fromJsonT(json['data']), ); } } class DataModel { int id; String name; DataModel({required this.id, required this.name}); factory DataModel.fromJson(Map<String, dynamic> json) { return DataModel( id: json['id'], name: json['name'], ); } }

2. Parse the JSON response using the defined model classes. You can create a function that converts the JSON into the desired model using generics:

ApiResponse<T> parseJson<T>(String jsonString, Function fromJsonT) { final jsonData = json.decode(jsonString); return ApiResponse.fromJson(jsonData, fromJsonT); }

3. Invoke the parsing function by passing the JSON response and the model class to generate the desired object:

String jsonResponse = ''' { "status":"200", "message":"Data fetch success", "data":[ { "id":0, "name":"Soton" } ] } '''; ApiResponse<List<DataModel>> response = parseJson<List<DataModel>>( jsonResponse, (data) => List<DataModel>.from(data.map((x) => DataModel.fromJson(x))), ); print(response.status); // 200 print(response.message); // Data fetch success print(response.data[0].id); // 0 print(response.data[0].name); // Soton

By using generics and the defined model classes, you can parse your JSON response into Flutter objects while maintaining type safety and reusability.

final responseStr = await postService(payload: {
  "email": "jobayer.m360ict@gmail.com",
  "password": "123456789"
});


ApiResponse<UsersModel> response = parseJson<UsersModel>(
  responseStr,
      (data) =>  UsersModel.fromJson(data),
);

print(response.success); // 200
print(response.message); // Data fetch success
print(response.data?.name); // 0
print(response.data?.email); // Soton

import 'dart:async';
import 'dart:convert';
import 'dart:io';
import 'package:http/http.dart' as http;

Future<String> postService({required Map<String,String> payload}) async {
  Uri url = Uri.parse("https://server.evaluation360.world/api/v1/auth/upc/login");

  final Map<String, String> header = {
    "Content-Type": "application/json",
  };


  try {
    final response =
    await http.post(url, body: jsonEncode(payload), headers: header);


    return response.body;

  } on TimeoutException catch (e) {
    return '''
{
   "status": "300",
   "message": "Data fetch timeout",
   "data": null
}
''';
  } on SocketException catch (e) {

    return '''
{
   "status": "400",
   "message": "Data fetch failed no internet",
   "data": null
}
''';
  } catch (e) {

    return '''
{
   "status": "500",
   "message": "Data fetch failed",
   "data": null
}
''';
  }
}



// To parse this JSON data, do
//
//     final usersModel = usersModelFromJson(jsonString);

// import 'dart:convert';

// UsersModel usersModelFromJson(String str) => UsersModel.fromJson(json.decode(str));

// String usersModelToJson(UsersModel data) => json.encode(data.toJson());

class UsersModel {
  int? id;
  String? name;
  dynamic phone;
  String? email;
  dynamic photo;
  dynamic nidFront;
  dynamic nidBack;
  dynamic country;
  dynamic city;
  dynamic address;
  String? status;
  DateTime? createdAt;

  UsersModel({
    this.id,
    this.name,
    this.phone,
    this.email,
    this.photo,
    this.nidFront,
    this.nidBack,
    this.country,
    this.city,
    this.address,
    this.status,
    this.createdAt,
  });

  factory UsersModel.fromJson(Map<String, dynamic> json) => UsersModel(
    id: json["id"],
    name: json["name"],
    phone: json["phone"],
    email: json["email"],
    photo: json["photo"],
    nidFront: json["nid_front"],
    nidBack: json["nid_back"],
    country: json["country"],
    city: json["city"],
    address: json["address"],
    status: json["status"],
    createdAt: json["created_at"] == null ? null : DateTime.parse(json["created_at"]),
  );

}



class ApiResponse<T> {
  bool? success;
  String? message;
  T? data;

  ApiResponse({this.success, this.message, this.data});

  factory ApiResponse.fromJson(Map<String, dynamic> json, Function fromJsonT) {
    return ApiResponse(
      success: json['status'],
      message: json['message'],
      data: fromJsonT(json['data']),
    );
  }
}



import 'dart:convert';

import 'package:demo/api_response.dart';

ApiResponse<T> parseJson<T>(String jsonString, Function fromJsonT) {
  try{
    final jsonData = json.decode(jsonString);
    return ApiResponse.fromJson(jsonData, fromJsonT);
  }on FormatException catch (e) {
    return ApiResponse(success: false, message: "Invalid JSON format: $e");
  }
  catch(e){
    return ApiResponse(success: false, message: "Error parsing data: $e");
  }
}