BehaviorSubject<T> class

A special StreamController that captures the latest item that has been added to the controller, and emits that as the first item to any new listener.

This subject allows sending data, error and done events to the listener. The latest item that has been added to the subject will be sent to any new listeners of the subject. After that, any new events will be appropriately sent to the listeners. It is possible to provide a seed value that will be emitted if no items have been added to the subject.

BehaviorSubject is, by default, a broadcast (aka hot) controller, in order to fulfill the Rx Subject contract. This means the Subject's stream can be listened to multiple times.

Example

final subject = BehaviorSubject<int>();

subject.add(1);
subject.add(2);
subject.add(3);

subject.stream.listen(print); // prints 3
subject.stream.listen(print); // prints 3
subject.stream.listen(print); // prints 3

Example with seed value

final subject = BehaviorSubject<int>.seeded(1);

subject.stream.listen(print); // prints 1
subject.stream.listen(print); // prints 1
subject.stream.listen(print); // prints 1
Inheritance
Implemented types
Available extensions

Constructors

BehaviorSubject({void onListen()?, void onCancel()?, bool sync = false})
Constructs a BehaviorSubject, optionally pass handlers for onListen, onCancel and a flag to handle events sync.
factory
BehaviorSubject.seeded(T seedValue, {void onListen()?, void onCancel()?, bool sync = false})
Constructs a BehaviorSubject, optionally pass handlers for onListen, onCancel and a flag to handle events sync.
factory

Properties

done → Future
A future which is completed when the stream controller is done sending events.
no setterinherited
error → Object?

Available on ValueStream<T>, provided by the ValueStreamExtensions extension

Last emitted error, or null if no error added or value exists.
no setter
errorAndStackTrace → ErrorAndStackTrace?
Last emitted error and the corresponding stack trace, or null if no error added or value exists. See hasError
no setteroverride
first → Future<T>
The first element of this stream.
no setterinherited
hasError → bool

Available on ValueStream<T>, provided by the ValueStreamExtensions extension

A flag that turns true as soon as at an error event has been emitted.
no setter
hashCode → int
The hash code for this object.
no setterinherited
hasListener → bool
Whether there is a subscriber on the Stream.
no setterinherited
hasValue → bool

Available on ValueStream<T>, provided by the ValueStreamExtensions extension

A flag that turns true as soon as at least one event has been emitted.
no setter
isBroadcast → bool
Whether this stream is a broadcast stream.
no setterinherited
isClosed → bool
Whether the stream controller is closed for adding more events.
no setterinherited
isEmpty → Future<bool>
Whether this stream contains any elements.
no setterinherited
isPaused → bool
Whether the subscription would need to buffer events.
no setterinherited
last → Future<T>
The last element of this stream.
no setterinherited
length → Future<int>
The number of elements in this stream.
no setterinherited
onCancel ↔ ControllerCancelCallback?
The callback which is called when the stream is canceled.
getter/setter pairinherited
onListen ↔ ControllerCallback?
The callback which is called when the stream is listened to.
getter/setter pairinherited
onPause ↔ ControllerCallback
The callback which is called when the stream is paused.
getter/setter pairinherited
onResume ↔ ControllerCallback
The callback which is called when the stream is resumed.
getter/setter pairinherited
requireError → Object

Available on ValueStream<T>, provided by the ValueStreamExtensions extension

Last emitted error, or throws "Null check operator used on a null value" error if no error added or value exists.
no setter
requireValue → T

Available on ValueStream<T>, provided by the ValueStreamExtensions extension

Returns last emitted value, or throws "Null check operator used on a null value" error if there has been no emission yet.
no setter
runtimeType → Type
A representation of the runtime type of the object.
no setterinherited
single → Future<T>
The single element of this stream.
no setterinherited
sink → StreamSink<T>
Returns a view of this object that only exposes the StreamSink interface.
no setterinherited
stream → ValueStream<T>
The stream that this controller is controlling.
no setteroverride
value → T?

Available on ValueStream<T>, provided by the ValueStreamExtensions extension

Returns last emitted value, or null if there has been no emission yet.
no setter
valueWrapper → ValueWrapper<T>?
Last emitted value wrapped in ValueWrapper, or null if there has been no emission yet. To indicate that the latest value is null, return ValueWrapper(null). See hasValue
no setteroverride

Methods

add(T event) → void
Sends a data event.
inherited
addError(Object error, [StackTrace? stackTrace]) → void
Sends or enqueues an error event.
inherited
addStream(Stream<T> source, {bool? cancelOnError}) → Future<void>
Receives events from source and puts them into this controller's stream.
inherited
any(bool test(T element)) → Future<bool>
Checks whether test accepts any element provided by this stream.
inherited
asBroadcastStream({void onListen(StreamSubscription<T> subscription)?, void onCancel(StreamSubscription<T> subscription)?}) → Stream<T>
Returns a multi-subscription stream that produces the same events as this.
inherited
asyncExpand<E>(Stream<E>? convert(T event)) → ValueStream<E>
Transforms each element into a sequence of asynchronous events.
override
asyncMap<E>(FutureOr<E> convert(T event)) → ValueStream<E>
Creates a new stream with each data event of this stream asynchronously mapped to a new event.
override
cast<R>() → ValueStream<R>
Adapt this stream to be a Stream<R>.
override
close() → Future
Closes the stream.
inherited
contains(Object? needle) → Future<bool>
Returns whether needle occurs in the elements provided by this stream.
inherited
createForwardingSubject<R>({void onListen()?, void onCancel()?, bool sync = false}) → BehaviorSubject<R>
Creates a trampoline StreamController, which can forward events in the same manner as the original Subject does. e.g. replay or behavior on subscribe.
override
debounce(Stream window(T event)) → Stream<T>

Available on Stream<T>, provided by the DebounceExtensions extension

Transforms a Stream so that will only emit items from the source sequence if a window has completed, without the source sequence emitting another item.
debounceTime(Duration duration) → Stream<T>

Available on Stream<T>, provided by the DebounceExtensions extension

Transforms a Stream so that will only emit items from the source sequence whenever the time span defined by duration passes, without the source sequence emitting another item.
distinct([bool equals(T previous, T next)?]) → ValueStream<T>
Skips data events if they are equal to the previous data event.
override
drain<E>([E? futureValue]) → Future<E>
Discards all data on this stream, but signals when it is done or an error occurred.
inherited
elementAt(int index) → Future<T>
Returns the value of the indexth data event of this stream.
inherited
every(bool test(T element)) → Future<bool>
Checks whether test accepts all elements provided by this stream.
inherited
expand<S>(Iterable<S> convert(T element)) → ValueStream<S>
Transforms each element of this stream into a sequence of elements.
override
firstWhere(bool test(T element), {T orElse()?}) → Future<T>
Finds the first element of this stream matching test.
inherited
fold<S>(S initialValue, S combine(S previous, T element)) → Future<S>
Combines a sequence of values by repeatedly applying combine.
inherited
forEach(void action(T element)) → Future<void>
Executes action on each element of this stream.
inherited
handleError(Function onError, {bool test(dynamic error)?}) → ValueStream<T>
Creates a wrapper Stream that intercepts some errors from this stream.
override
join([String separator = ""]) → Future<String>
Combines the string representation of elements into a single string.
inherited
lastWhere(bool test(T element), {T orElse()?}) → Future<T>
Finds the last element in this stream matching test.
inherited
listen(void onData(T value)?, {Function? onError, void onDone()?, bool? cancelOnError}) → StreamSubscription<T>
Adds a subscription to this stream.
inherited
map<S>(S convert(T event)) → ValueStream<S>
Transforms each element of this stream into a new stream event.
override
mergeWith(Iterable<Stream<T>> streams) → Stream<T>

Available on Stream<T>, provided by the MergeExtension extension

Combines the items emitted by multiple streams into a single stream of items. The items are emitted in the order they are emitted by their sources.
noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent method or property is accessed.
inherited
onAdd(T event) → void
An extension point for sub-classes. Perform any side-effect / state management you need to here, rather than overriding the add method directly.
override
onAddError(Object error, [StackTrace? stackTrace]) → void
An extension point for sub-classes. Perform any side-effect / state management you need to here, rather than overriding the add method directly.
override
pipe(StreamConsumer<T> streamConsumer) → Future
Pipes the events of this stream into streamConsumer.
inherited
reduce(T combine(T previous, T element)) → Future<T>
Combines a sequence of values by repeatedly applying combine.
inherited
singleWhere(bool test(T element), {T orElse()?}) → Future<T>
Finds the single element in this stream matching test.
inherited
skip(int count) → ValueStream<T>
Skips the first count data events from this stream.
override
skipWhile(bool test(T element)) → ValueStream<T>
Skip data events from this stream while they are matched by test.
override
startWith(T startValue) → Stream<T>

Available on Stream<T>, provided by the StartWithExtension extension

Prepends a value to the source Stream.
switchMap<S>(Stream<S> mapper(T value)) → Stream<S>

Available on Stream<T>, provided by the SwitchMapExtension extension

Converts each emitted item into a Stream using the given mapper function. The newly created Stream will be be listened to and begin emitting items, and any previously created Stream will stop emitting.
take(int count) → ValueStream<T>
Provides at most the first count data events of this stream.
override
takeWhile(bool test(T element)) → ValueStream<T>
Forwards data events while test is successful.
override
timeout(Duration timeLimit, {void onTimeout(EventSink<T> sink)?}) → ValueStream<T>
Creates a new stream with the same events as this stream.
override
toList() → Future<List<T>>
Collects all elements of this stream in a List.
inherited
toSet() → Future<Set<T>>
Collects the data of this stream in a Set.
inherited
toString() → String
A string representation of this object.
inherited
transform<S>(StreamTransformer<T, S> streamTransformer) → ValueStream<S>
Applies streamTransformer to this stream.
override
where(bool test(T event)) → ValueStream<T>
Creates a new stream from this stream that discards some elements.
override

Operators

operator ==(Object other) → bool
The equality operator.
inherited