flutter_bloc library

Flutter widgets that make it easy to implement the BLoC design pattern. Built to be used with the bloc state management package.

Get started at bloclibrary.dev 🚀

Classes

Bloc<Event, State>
Takes a Stream of Events as input and transforms them into a Stream of States as output.
BlocBase<State>
An interface for the core functionality implemented by both Bloc and Cubit.
BlocBuilder<B extends BlocBase<S>, S>
BlocBuilder handles building a widget in response to new states. BlocBuilder is analogous to StreamBuilder but has simplified API to reduce the amount of boilerplate code needed as well as bloc-specific performance improvements. Please refer to BlocListener if you want to "do" anything in response to state changes such as navigation, showing a dialog, etc...
BlocBuilderBase<B extends BlocBase<S>, S>
Base class for widgets that build themselves based on interaction with a specified bloc.
BlocConsumer<B extends BlocBase<S>, S>
BlocConsumer exposes a builder and listener in order react to new states. BlocConsumer is analogous to a nested BlocListener and BlocBuilder but reduces the amount of boilerplate needed. BlocConsumer should only be used when it is necessary to both rebuild UI and execute other reactions to state changes in the bloc.
BlocListener<B extends BlocBase<S>, S>
Takes a BlocWidgetListener and an optional bloc and invokes the listener in response to state changes in the bloc. It should be used for functionality that needs to occur only in response to a state change such as navigation, showing a SnackBar, showing a Dialog, etc... The listener is guaranteed to only be called once for each state change unlike the builder in BlocBuilder.
BlocListenerBase<B extends BlocBase<S>, S>
Base class for widgets that listen to state changes in a specified bloc.
BlocObserver
An interface for observing the behavior of Bloc instances.
BlocProvider<T extends BlocBase<Object?>>
Takes a Create function that is responsible for creating the Bloc or Cubit and a child which will have access to the instance via BlocProvider.of(context). It is used as a dependency injection (DI) widget so that a single instance of a Bloc or Cubit can be provided to multiple widgets within a subtree.
BlocSelector<B extends BlocBase<S>, S, T>
BlocSelector is analogous to BlocBuilder but allows developers to filter updates by selecting a new value based on the bloc state. Unnecessary builds are prevented if the selected value does not change.
Change<State>
A Change represents the change from one State to another. A Change consists of the currentState and nextState.
Cubit<State>
A Cubit is similar to Bloc but has no notion of events and relies on methods to emit new states.
Emitter<State>
An Emitter is a class which is capable of emitting new states.
MultiBlocListener
Merges multiple BlocListener widgets into one widget tree.
MultiBlocProvider
Merges multiple BlocProvider widgets into one widget tree.
MultiRepositoryProvider
Merges multiple RepositoryProvider widgets into one widget tree.
RepositoryProvider<T>
Takes a Create function that is responsible for creating the repository and a child which will have access to the repository via RepositoryProvider.of(context). It is used as a dependency injection (DI) widget so that a single instance of a repository can be provided to multiple widgets within a subtree.
Transition<Event, State>
A Transition is the change from one state to another. Consists of the currentState, an event, and the nextState.

Extensions

ReadContext on BuildContext
Exposes the read method.
SelectContext on BuildContext
Adds a select method on BuildContext.
WatchContext on BuildContext
Exposes the watch method.

Typedefs

BlocBuilderCondition<S> = bool Function(S previous, S current)
Signature for the buildWhen function which takes the previous state and the current state and is responsible for returning a bool which determines whether to rebuild BlocBuilder with the current state.
BlocListenerCondition<S> = bool Function(S previous, S current)
Signature for the listenWhen function which takes the previous state and the current state and is responsible for returning a bool which determines whether or not to call BlocWidgetListener of BlocListener with the current state.
BlocWidgetBuilder<S> = Widget Function(BuildContext context, S state)
Signature for the builder function which takes the BuildContext and state and is responsible for returning a widget which is to be rendered. This is analogous to the builder function in StreamBuilder.
BlocWidgetListener<S> = void Function(BuildContext context, S state)
Signature for the listener function which takes the BuildContext along with the state and is responsible for executing in response to state changes.
BlocWidgetSelector<S, T> = T Function(S state)
Signature for the selector function which is responsible for returning a selected value, T, based on state.
EventHandler<Event, State> = FutureOr<void> Function(Event event, Emitter<State> emit)
An event handler is responsible for reacting to an incoming Event and can emit zero or more states via the Emitter.
EventMapper<Event> = Stream<Event> Function(Event event)
Signature for a function which converts an incoming event into an outbound stream of events. Used when defining custom EventTransformers.
EventTransformer<Event> = Stream<Event> Function(Stream<Event> events, EventMapper<Event> mapper)
Used to change how events are processed. By default events are processed concurrently.
TransitionFunction<Event, State> = Stream<Transition<Event, State>> Function(Event)
@Deprecated - Use on<Event> with an EventTransformer instead. Will be removed in v8.0.0

Exceptions / Errors

BlocUnhandledErrorException
Exception thrown when an unhandled error occurs within a bloc.
ProviderNotFoundException
The error that will be thrown if Provider.of fails to find a Provider as an ancestor of the BuildContext used.