How do i handle errors in Dio package

Question

okay so im using dio package to authenticate users in my app. it works fine but i want to be able to show the error message in a toast message for the user and i have absolutely no idea how to do that. i tried printing the error but i get no response, please help me out im new to dio.

This is my code

 class Loginservice extends ILogin {
  @override
  Future<UserModel?> login(
      String username, String password, BuildContext context) async {
    @override
    SharedPreferences preferences = await SharedPreferences.getInstance();

    String api = '$baseUrl/login';

    final data = {"username": username, "pwd": password};
    final dio = Dio();
    Response response;
    response = await dio.post(api, data: data);
    if (response.statusCode == 200) {
      final body = response.data;
      var username = body['username'];
      var myToken = body['token'];
      preferences.setString('username', username);
      preferences.setBool('isLoggedIn', true);

          Navigator.push(
              context, MaterialPageRoute(builder: (context) => MainScreen()));
    
          return UserModel(
            username: username,
            token: body['token'],
          );
        } else {
          print('error');
        }
      }
    }

Answer 1

As mentioned in their docs,

When an error occurs, Dio will wrap the Error/Exception to a DioException:

You can wrap the call with a try/ catch to catch them.

try {
  // 404
  await dio.get('https://api.pub.dev/not-exist');
} on DioException catch (e) {
  // The request was made and the server responded with a status code
  // that falls out of the range of 2xx and is also not 304.
  if (e.response != null) {
    print(e.response.data)
    print(e.response.headers)
    print(e.response.requestOptions)
  } else {
    // Something happened in setting up or sending the request that triggered an Error
    print(e.requestOptions)
    print(e.message)
  }
}

and DioException contain these fields,

/// The request info for the request that throws exception.
RequestOptions requestOptions;

/// Response info, it may be `null` if the request can't reach to the
/// HTTP server, for example, occurring a DNS error, network is not available.
Response? response;

/// The type of the current [DioException].
DioExceptionType type;

/// The original error/exception object;
/// It's usually not null when `type` is [DioExceptionType.unknown].
Object? error;

/// The stacktrace of the original error/exception object;
/// It's usually not null when `type` is [DioExceptionType.unknown].
StackTrace? stackTrace;

/// The error message that throws a [DioException].
String? message;

Personally, I would use a switch statement to catch all the DioExceptionType s and handle/ return error messages accordingly.

if (error is DioException) {
      switch (error.type) {
        case DioExceptionType.connectionTimeout:
        case DioExceptionType.receiveTimeout:
        case DioExceptionType.sendTimeout:
          networkFailure = const NetworkFailure.requestTimeout();
          break;
        case DioExceptionType.badCertificate:
          networkFailure = const NetworkFailure.badCertificate();
    ...

you can find all the exception types here or you can simply go to the plugin source in your flutter app.