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
  • Object
  • Subject<T>
  • BehaviorSubject
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

hasValue → bool
A flag that turns true as soon as at least one event has been emitted.
read-only, override
stream → ValueStream<T>
The stream that this controller is controlling.
read-only, override
value ↔ T
Get the latest value emitted by the Subject
read / write, override-getter
done → Future
Return a future which is completed when the StreamSink is finished. [...]
read-only, inherited
first → Future<T>
The first element of this stream.
read-only, inherited
hashCode → int
The hash code for this object.
read-only, inherited
hasListener → bool
Whether there is a subscriber on the Stream.
read-only, inherited
isBroadcast → bool
Whether this stream is a broadcast stream.
read-only, inherited
isClosed → bool
Whether the stream controller is closed for adding more events. [...]
read-only, inherited
isEmpty → Future<bool>
Whether this stream contains any elements.
read-only, inherited
isPaused → bool
Whether the subscription would need to buffer events. [...]
read-only, inherited
last → Future<T>
The last element of this stream.
read-only, inherited
length → Future<int>
The number of elements in this stream.
read-only, inherited
onCancel ↔ ControllerCancelCallback
The callback which is called when the stream is canceled. [...]
read / write, inherited
onListen ↔ ControllerCallback
The callback which is called when the stream is listened to. [...]
read / write, inherited
onPause ↔ ControllerCallback
The callback which is called when the stream is paused. [...]
read / write, inherited
onResume ↔ ControllerCallback
The callback which is called when the stream is resumed. [...]
read / write, inherited
runtimeType → Type
A representation of the runtime type of the object.
read-only, inherited
single → Future<T>
The single element of this stream.
read-only, inherited
sink → StreamSink<T>
Returns a view of this object that only exposes the StreamSink interface.
read-only, inherited

Methods

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
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: true}) → Future
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)) → Stream<E>
Transforms each element into a sequence of asynchronous events.
inherited
asyncMap<E>(FutureOr<E> convert(T event)) → Stream<E>
Creates a new stream with each data event of this stream asynchronously mapped to a new event.
inherited
cast<R>() → Stream<R>
Adapt this stream to be a Stream<R>.
inherited
close() → Future
Closes the stream. [...]
inherited
contains(Object needle) → Future<bool>
Returns whether needle occurs in the elements provided by this stream.
inherited
distinct([bool equals(T previous, T next)]) → Stream<T>
Skips data events if they are equal to the previous data event.
inherited
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)) → Stream<S>
Transforms each element of this stream into a sequence of elements.
inherited
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
Executes action on each element of this stream.
inherited
handleError(Function onError, {bool test(dynamic error)}) → Stream<T>
Creates a wrapper Stream that intercepts some errors from this stream.
inherited
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)) → Stream<S>
Transforms each element of this stream into a new stream event.
inherited
noSuchMethod(Invocation invocation) → dynamic
Invoked when a non-existent method or property is accessed.
inherited
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) → Stream<T>
Skips the first count data events from this stream.
inherited
skipWhile(bool test(T element)) → Stream<T>
Skip data events from this stream while they are matched by test.
inherited
take(int count) → Stream<T>
Provides at most the first count data events of this stream.
inherited
takeWhile(bool test(T element)) → Stream<T>
Forwards data events while test is successful.
inherited
timeout(Duration timeLimit, {void onTimeout(EventSink<T> sink)}) → Stream<T>
Creates a new stream with the same events as this stream.
inherited
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
Returns a string representation of this object.
inherited
transform<S>(StreamTransformer<T, S> streamTransformer) → Stream<S>
Applies streamTransformer to this stream.
inherited
where(bool test(T event)) → Stream<T>
Creates a new stream from this stream that discards some elements.
inherited

Operators

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