api_state

A lightweight, zero-dependency Dart package for representing API call states using sealed classes.

Built for Dart 3+ with compile-time exhaustive pattern matching. Works with any state management solution — Bloc, Riverpod, GetX, Provider, or plain setState.

States

State	Class	Description
Initial	ApiInitial	No action taken yet
Loading	ApiLoading	API call in progress
Success	ApiSuccess<T>	Completed with data
Failure	ApiFailure<T>	Failed with error
Refresh	ApiRefresh<T>	Re-fetching while showing existing data

Installation

dependencies:
  api_state: ^1.0.0

import 'package:api_state/api_state.dart';

Quick Start

// Define your failure types
class ServerFailure extends Failure {
  const ServerFailure(super.message, {super.code, super.stackTrace});
}

class NetworkFailure extends Failure {
  const NetworkFailure([super.message = 'No internet connection']);
}

// Use in your state management
ApiStatus<List<User>> usersState = const ApiInitial();

Future<void> fetchUsers() async {
  usersState = const ApiLoading();

  usersState = await ApiStatus.guard(
    () => repository.fetchUsers(),
    onError: (e, st) => ServerFailure(e.toString(), stackTrace: st),
  );
}

Pattern Matching

Dart 3 Switch Expression

The compiler ensures you handle every case:

Widget build(BuildContext context) {
  return switch (usersState) {
    ApiInitial()              => const SizedBox.shrink(),
    ApiLoading()              => const CircularProgressIndicator(),
    ApiSuccess(:final data)   => UserList(users: data),
    ApiFailure(:final error)  => ErrorView(message: error.message),
    ApiRefresh(:final data)   => UserList(users: data, refreshing: true),
  };
}

when — Exhaustive Callbacks

Groups initial and loading into a single callback:

final widget = usersState.when(
  initialOrLoading: () => const CircularProgressIndicator(),
  success: (users) => UserList(users: users),
  failure: (error) => ErrorView(message: error.message),
  refresh: (users) => UserList(users: users, refreshing: true), // optional
);

whenOrNull — Handle Only What You Need

Unhandled states return null:

usersState.whenOrNull(
  success: (users) => showSnackBar('Loaded ${users.length} users'),
  failure: (error) => showSnackBar(error.message),
);

maybeWhen — With Fallback

final message = usersState.maybeWhen(
  success: (users) => '${users.length} users',
  orElse: () => 'No data yet',
);

Convenience Getters

usersState.isInitial;  // true if ApiInitial
usersState.isLoading;  // true if ApiLoading
usersState.isSuccess;  // true if ApiSuccess
usersState.isFailure;  // true if ApiFailure
usersState.isRefresh;  // true if ApiRefresh

usersState.hasData;    // true if success or refresh
usersState.hasError;   // true if failure

usersState.data;       // T? — data from success/refresh, null otherwise
usersState.error;      // Failure? — error from failure, null otherwise

Transform Methods

map — Transform Data

Convert ApiStatus<T> to ApiStatus<R> without losing state info:

final ApiStatus<List<UserModel>> models = fetchResult;
final ApiStatus<List<UserViewModel>> viewModels = models.map(
  (users) => users.map(UserViewModel.fromModel).toList(),
);
// ApiSuccess<List<UserModel>> → ApiSuccess<List<UserViewModel>>
// ApiLoading/ApiFailure/etc pass through unchanged

mapFailure — Transform Errors

final uiState = repoState.mapFailure(
  (failure) => UserFriendlyFailure('Something went wrong'),
);

whenData — Callback for Any Data State

Fires for both success and refresh:

usersState.whenData((users) => cache.save(users));
// Returns null for initial/loading/failure

State Transitions

toLoading()

Transition to loading, discarding existing data:

usersState = usersState.toLoading();

toRefresh()

Transition to refresh, preserving existing data. Falls back to ApiLoading if no data exists:

// Pull-to-refresh: keep showing current list while re-fetching
usersState = usersState.toRefresh();
// ApiSuccess(users) → ApiRefresh(users)
// ApiInitial()      → ApiLoading() (no data to preserve)

ApiStatus.guard

Wraps an async call and returns ApiSuccess or ApiFailure automatically:

Future<void> fetchUsers() async {
  usersState = usersState.toLoading();

  usersState = await ApiStatus.guard(
    () => repository.fetchUsers(),
    onError: (error, stackTrace) => ServerFailure(
      error.toString(),
      stackTrace: stackTrace,
    ),
  );
}

Failure

Failure is abstract — extend it to define domain-specific error types:

class ServerFailure extends Failure {
  const ServerFailure(super.message, {super.code, super.stackTrace});
}

class NetworkFailure extends Failure {
  const NetworkFailure([super.message = 'No internet connection']);
}

class CacheFailure extends Failure {
  const CacheFailure([super.message = 'Cache read failed']);
}

class ValidationFailure extends Failure {
  final Map<String, String> fieldErrors;

  const ValidationFailure(this.fieldErrors)
      : super('Validation failed');
}

Each failure carries:

Field	Type	Description
message	String	Human-readable error message
code	int?	Optional error code (e.g. HTTP status)
stackTrace	StackTrace?	Optional stack trace for debugging

Full Example with Bloc

class UsersCubit extends Cubit<ApiStatus<List<User>>> {
  final UserRepository _repository;

  UsersCubit(this._repository) : super(const ApiInitial());

  Future<void> fetch() async {
    emit(const ApiLoading());
    emit(await ApiStatus.guard(
      () => _repository.getUsers(),
      onError: (e, st) => ServerFailure(e.toString(), stackTrace: st),
    ));
  }

  Future<void> refresh() async {
    emit(state.toRefresh());
    emit(await ApiStatus.guard(
      () => _repository.getUsers(),
      onError: (e, st) => ServerFailure(e.toString(), stackTrace: st),
    ));
  }
}

// In your widget
BlocBuilder<UsersCubit, ApiStatus<List<User>>>(
  builder: (context, state) => switch (state) {
    ApiInitial()              => const SizedBox.shrink(),
    ApiLoading()              => const CircularProgressIndicator(),
    ApiSuccess(:final data)   => UserList(users: data),
    ApiFailure(:final error)  => ErrorView(message: error.message),
    ApiRefresh(:final data)   => UserList(users: data, refreshing: true),
  },
)

API Reference

ApiStatus

Method / Getter	Return Type	Description
isInitial, isLoading, isSuccess, isFailure, isRefresh	bool	State checks
hasData, hasError	bool	Data/error availability
data	T?	Data from success/refresh
error	Failure?	Error from failure
when(...)	R	Exhaustive pattern matching
whenOrNull(...)	R?	Partial matching, returns null
maybeWhen(...)	R	Partial matching with fallback
whenData(callback)	R?	Callback for data states
map(transform)	ApiStatus<R>	Transform data type
mapFailure(transform)	ApiStatus<T>	Transform error type
toLoading()	ApiStatus<T>	Transition to loading
toRefresh()	ApiStatus<T>	Transition to refresh (preserves data)
ApiStatus.guard(action, onError:)	Future<ApiStatus<T>>	Wrap async call