dependencies:
  flutter:
    sdk: flutter
  cupertino_icons: ^0.1.3
  dio: 3.0.8
  freezed: 0.10.9
  flutter_bloc: 5.0.0

dev_dependencies:
  flutter_test:
    sdk: flutter
  build_runner:

import 'package:dio/dio.dart';
import 'package:network_handling/services/dio_client.dart';

class APIRepository {
  DioClient dioClient;
  String _baseUrl = "";

  APIRepository() {
    var dio = Dio();

    dioClient = DioClient(_baseUrl, dio);
  }
}

import 'package:flutter/foundation.dart';
import 'package:freezed_annotation/freezed_annotation.dart';

import 'network_exceptions.dart';


part 'api_result.freezed.dart';

@freezed
abstract class ApiResult<T> with _$ApiResult<T> {
  const factory ApiResult.success({@required T data}) = Success<T>;

  const factory ApiResult.failure({@required NetworkExceptions error}) =
      Failure<T>;
}

import 'dart:io';

import 'package:dio/dio.dart';
import 'package:freezed_annotation/freezed_annotation.dart';

part 'network_exceptions.freezed.dart';

@freezed
abstract class NetworkExceptions with _$NetworkExceptions {
  const factory NetworkExceptions.requestCancelled() = RequestCancelled;

  const factory NetworkExceptions.unauthorisedRequest() = UnauthorisedRequest;

  const factory NetworkExceptions.badRequest() = BadRequest;

  const factory NetworkExceptions.notFound(String reason) = NotFound;

  const factory NetworkExceptions.methodNotAllowed() = MethodNotAllowed;

  const factory NetworkExceptions.notAcceptable() = NotAcceptable;

  const factory NetworkExceptions.requestTimeout() = RequestTimeout;

  const factory NetworkExceptions.sendTimeout() = SendTimeout;

  const factory NetworkExceptions.conflict() = Conflict;

  const factory NetworkExceptions.internalServerError() = InternalServerError;

  const factory NetworkExceptions.notImplemented() = NotImplemented;

  const factory NetworkExceptions.serviceUnavailable() = ServiceUnavailable;

  const factory NetworkExceptions.noInternetConnection() = NoInternetConnection;

  const factory NetworkExceptions.formatException() = FormatException;

  const factory NetworkExceptions.unableToProcess() = UnableToProcess;

  const factory NetworkExceptions.defaultError(String error) = DefaultError;

  const factory NetworkExceptions.unexpectedError() = UnexpectedError;

}

- Run this command in terminal to watch auto change

- Run this command in terminal to watch auto change and delete previously generated files

####Create a new method in NetworkExceptions class which will return NetworkExceptions

```dart


  static NetworkExceptions getDioException(error) {
    if (error is Exception) {
      try {
        NetworkExceptions networkExceptions;
        if (error is DioError) {
          switch (error.type) {
            case DioErrorType.CANCEL:
              networkExceptions = NetworkExceptions.requestCancelled();
              break;
            case DioErrorType.CONNECT_TIMEOUT:
              networkExceptions = NetworkExceptions.requestTimeout();
              break;
            case DioErrorType.DEFAULT:
              networkExceptions = NetworkExceptions.noInternetConnection();
              break;
            case DioErrorType.RECEIVE_TIMEOUT:
              networkExceptions = NetworkExceptions.sendTimeout();
              break;
            case DioErrorType.RESPONSE:
              switch (error.response.statusCode) {
                case 400:
                  networkExceptions = NetworkExceptions.unauthorisedRequest();
                  break;
                case 401:
                  networkExceptions = NetworkExceptions.unauthorisedRequest();
                  break;
                case 403:
                  networkExceptions = NetworkExceptions.unauthorisedRequest();
                  break;
                case 404:
                  networkExceptions = NetworkExceptions.notFound("Not found");
                  break;
                case 409:
                  networkExceptions = NetworkExceptions.conflict();
                  break;
                case 408:
                  networkExceptions = NetworkExceptions.requestTimeout();
                  break;
                case 500:
                  networkExceptions = NetworkExceptions.internalServerError();
                  break;
                case 503:
                  networkExceptions = NetworkExceptions.serviceUnavailable();
                  break;
                default:
                  var responseCode = error.response.statusCode;
                  networkExceptions = NetworkExceptions.defaultError(
                    "Received invalid status code: $responseCode",
                  );
              }
              break;
            case DioErrorType.SEND_TIMEOUT:
              networkExceptions = NetworkExceptions.sendTimeout();
              break;
          }
        } else if (error is SocketException) {
          networkExceptions = NetworkExceptions.noInternetConnection();
        } else {
          networkExceptions = NetworkExceptions.unexpectedError();
        }
        return networkExceptions;
      } on FormatException catch (e) {
        // Helper.printError(e.toString());
        return NetworkExceptions.formatException();
      } catch (_) {
        return NetworkExceptions.unexpectedError();
      }
    } else {
      if (error.toString().contains("is not a subtype of")) {
        return NetworkExceptions.unableToProcess();
      } else {
        return NetworkExceptions.unexpectedError();
      }
    }
  }

  static String getErrorMessage(NetworkExceptions networkExceptions) {
    var errorMessage = "";
    networkExceptions.when(notImplemented: () {
      errorMessage = "Not Implemented";
    }, requestCancelled: () {
      errorMessage = "Request Cancelled";
    }, internalServerError: () {
      errorMessage = "Internal Server Error";
    }, notFound: (String reason) {
      errorMessage = reason;
    }, serviceUnavailable: () {
      errorMessage = "Service unavailable";
    }, methodNotAllowed: () {
      errorMessage = "Method Allowed";
    }, badRequest: () {
      errorMessage = "Bad request";
    }, unauthorisedRequest: () {
      errorMessage = "Unauthorised request";
    }, unexpectedError: () {
      errorMessage = "Unexpected error occurred";
    }, requestTimeout: () {
      errorMessage = "Connection request timeout";
    }, noInternetConnection: () {
      errorMessage = "No internet connection";
    }, conflict: () {
      errorMessage = "Error due to a conflict";
    }, sendTimeout: () {
      errorMessage = "Send timeout in connection with API server";
    }, unableToProcess: () {
      errorMessage = "Unable to process the data";
    }, defaultError: (String error) {
      errorMessage = error;
    }, formatException: () {
      errorMessage = "Unexpected error occurred";
    }, notAcceptable: () {
      errorMessage = "Not acceptable";
    });
    return errorMessage;
  }

import 'package:dio/dio.dart';
import 'package:network_handling/model/movie_response.dart';
import 'package:network_handling/services/api_result.dart';
import 'package:network_handling/services/dio_client.dart';
import 'package:network_handling/services/network_exceptions.dart';

class APIRepository {
  DioClient dioClient;
  final String _apiKey = <apikey>;
  String _baseUrl = "http://api.themoviedb.org/3/";

  APIRepository() {
    var dio = Dio();

    dioClient = DioClient(_baseUrl, dio);
  }

  Future<ApiResult<List<Movie>>> fetchMovieList() async {
    try {
      final response = await dioClient
          .get("movie/popular", queryParameters: {"api_key": _apiKey});
      List<Movie> movieList = MovieResponse.fromJson(response).results;
      return ApiResult.success(data: movieList);
    } catch (e) {
      return ApiResult.failure(error: NetworkExceptions.getDioException(e));
    }
  }
}

import 'package:flutter/foundation.dart';
import 'package:freezed_annotation/freezed_annotation.dart';

part 'movie_event.freezed.dart';

@freezed
abstract class MovieEvent with _$MovieEvent {
  const factory MovieEvent.loadMovie() = LoadMovies;
}

import 'package:flutter/foundation.dart';
import 'package:freezed_annotation/freezed_annotation.dart';
import 'package:network_handling/services/network_exceptions.dart';

part 'result_state.freezed.dart';

@freezed
abstract class ResultState<T> with _$ResultState<T> {
  const factory ResultState.idle() = Idle<T>;

  const factory ResultState.loading() = Loading<T>;

  const factory ResultState.data({@required T data}) = Data<T>;

  const factory ResultState.error({@required NetworkExceptions error}) =
      Error<T>;
}

flutter packages pub run build_runner build

import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:network_handling/api_repository.dart';
import 'package:network_handling/bloc/movie/movie_event.dart';
import 'package:network_handling/bloc/movie/result_state.dart';
import 'package:network_handling/model/movie_response.dart';

class MovieBloc extends Bloc<MovieEvent, ResultState<List<Movie>>> {
  final APIRepository apiRepository;

  MovieBloc({this.apiRepository})
      : assert(apiRepository != null),
        super(Idle());

  @override
  Stream<ResultState<List<Movie>>> mapEventToState(MovieEvent event) {

  }
}

class MovieBloc extends Bloc<MovieEvent, ResultState<List<Movie>>> {
  final APIRepository apiRepository;

  MovieBloc({this.apiRepository})
      : assert(apiRepository != null),
        super(Idle());

  @override
  Stream<ResultState<List<Movie>>> mapEventToState(MovieEvent event) async* {

    yield ResultState.loading();

    if (event is LoadMovies) {

      ApiResult<List<Movie>> apiResult = await apiRepository.fetchMovieList();

      yield* apiResult.when(success: (List<Movie> data) async* {

        yield ResultState.data(data: data);

      }, failure: (NetworkExceptions error) async* {

        yield ResultState.error(error: error);

      });
    }
  }
}

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MultiBlocProvider(
      providers: [
        BlocProvider<MovieBloc>(
          create: (BuildContext context) {
            return MovieBloc(apiRepository: APIRepository());
          },
          child: MyHomePage(),
        )
      ],
      child: MaterialApp(
        title: 'Flutter Demo',
        theme: ThemeData(
          primarySwatch: Colors.blue,
          visualDensity: VisualDensity.adaptivePlatformDensity,
        ),
        home: MyHomePage(),
      ),
    );
  }
}

  @override
  void initState() {

    context.bloc<MovieBloc>().add(LoadMovies());

    super.initState();
  }

BlocBuilder<MovieBloc, ResultState<List<Movie>>>(
        builder: (BuildContext context, ResultState<List<Movie>> state) {
          return state.when(
            loading: () {
              return Center(child: CircularProgressIndicator());
            },
            idle: () {
              return Container();
            },
            data: (List<Movie> data) {
              return dataWidget(data);
            },
            error: (NetworkExceptions error) {
              return Text(NetworkExceptions.getErrorMessage(error));
            },
          );
        },
      )

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  void initState() {
    context.bloc<MovieBloc>().add(LoadMovies());
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Movies"),
      ),
      body: BlocBuilder<MovieBloc, ResultState<List<Movie>>>(
        builder: (BuildContext context, ResultState<List<Movie>> state) {
          return state.when(
            loading: () {
              return Center(child: CircularProgressIndicator());
            },
            idle: () {
              return Container();
            },
            data: (List<Movie> data) {
              return dataWidget(data);
            },
            error: (NetworkExceptions error) {
              return Text(NetworkExceptions.getErrorMessage(error));
            },
          );
        },
      ),
    );
  }

  Widget dataWidget(List<Movie> data) {
    return ListView.builder(
      itemCount: data.length,
      itemBuilder: (BuildContext context, int index) {
        return Container(
          height: 300,
          width: 300,
          child: Card(
            elevation: 1,
            child: Image.network(
              "https://image.tmdb.org/t/p/w342${data[index].posterPath}",
            ),
          ),
        );
      },
    );
  }
}