core/packages/flutter_bloc/flutter_bloc library

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 StateStreamable<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 StateStreamable<S>, S>

Base class for widgets that build themselves based on interaction with a specified bloc.

BlocConsumer<B extends StateStreamable<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.

BlocEventSink<Event extends Object?>

An ErrorSink that supports adding events.

BlocListener<B extends StateStreamable<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 StateStreamable<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.

BlocOverrides

This class facilitates overriding BlocObserver and EventTransformer. It should be extended by another class in client code with overrides that construct a custom implementation. The implementation in this class defaults to the base blocObserver and eventTransformer implementation. For example:

BlocProvider<T extends StateStreamableSource<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 StateStreamable<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.

Closable

An object that must be closed when no longer in use.

Cubit<State>

A Cubit is similar to Bloc but has no notion of events and relies on methods to emit new states.

Emittable<State extends Object?>

An object that can emit new states.

Emitter<State>

An Emitter is a class which is capable of emitting new states.

ErrorSink

A generic destination for errors.

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.

StateStreamable<State>

A Streamable that provides synchronous access to the current state.

StateStreamableSource<State>

A StateStreamable that must be closed when no longer in use.

Streamable<State extends Object?>

An object that provides access to a stream of states over time.

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.

Exceptions / Errors

ProviderNotFoundException

The error that will be thrown if Provider.of fails to find a Provider as an ancestor of the BuildContext used.