ForkJoinStream<T, R> class

This operator is best used when you have a group of streams and only care about the final emitted value of each. One common use case for this is if you wish to issue multiple requests on page load (or some other event) and only want to take action when a response has been received for all.

In this way it is similar to how you might use Future.wait.

Be aware that if any of the inner streams supplied to forkJoin error you will lose the value of any other streams that would or have already completed if you do not catch the error correctly on the inner stream.

If you are only concerned with all inner streams completing successfully you can catch the error on the outside. It's also worth noting that if you have an stream that emits more than one item, and you are concerned with the previous emissions forkJoin is not the correct choice.

In these cases you may better off with an operator like combineLatest or zip.

If the provided streams is empty, the resulting sequence completes immediately without emitting any items and without any calls to the combiner function.

Basic Example

This constructor takes in an Iterable<Stream<T>> and outputs a Stream<Iterable<T>> whenever any of the values change from the source stream. This is useful with a dynamic number of source streams!

ForkJoinStream.list<String>([
  Stream.fromIterable(['a']),
  Stream.fromIterable(['b']),
  Stream.fromIterable(['C', 'D']),
])
.listen(print); //prints ['a', 'b', 'D']

Example with combiner

If you wish to combine the list of values into a new object before emitting, you can provide the combiner function to the constructor.

ForkJoinStream(
  [
    Stream.fromIterable(['a']),
    Stream.fromIterable(['b']),
    Stream.fromIterable(['C', 'D']),
  ],
  (values) => values.last,
)
.listen(print); //prints 'D'

Example with a specific number of Streams

If you wish to combine a specific number of Streams together with proper types information for the value of each Stream, use the join2 - join9 operators.

ForkJoinStream.join2(
  Stream.fromIterable([1]),
  Stream.fromIterable([2, 3]),
  (a, b) => a + b,
)
.listen(print); // prints 4

Inheritance

Object
Stream<R>
StreamView<R>
ForkJoinStream

Available extensions

Constructors

ForkJoinStream(Iterable<Stream<T>> streams, R combiner(List<T> values)): Constructs a Stream that awaits the last values of the Streams in streams, then calls the combiner to emit an event of type R. After this event, the Stream closes.

Properties

first → Future<R>: The first element of this stream.
no setterinherited
hashCode → int: The hash code for this object.
no setterinherited
isBroadcast → bool: Whether this stream is a broadcast stream.
no setterinherited
isEmpty → Future<bool>: Whether this stream contains any elements.
no setterinherited
last → Future<R>: The last element of this stream.
no setterinherited
length → Future<int>: The number of elements in this stream.
no setterinherited
runtimeType → Type: A representation of the runtime type of the object.
no setterinherited
single → Future<R>: The single element of this stream.
no setterinherited

Methods

any(bool test(R element)) → Future<bool>: Checks whether test accepts any element provided by this stream.
inherited
asBroadcastStream({void onListen(StreamSubscription<R> subscription)?, void onCancel(StreamSubscription<R> subscription)?}) → Stream<R>: Returns a multi-subscription stream that produces the same events as this.
inherited
asyncExpand<E>(Stream<E>? convert(R event)) → Stream<E>: Transforms each element into a sequence of asynchronous events.
inherited
asyncMap<E>(FutureOr<E> convert(R 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
contains(Object? needle) → Future<bool>: Returns whether needle occurs in the elements provided by this stream.
inherited
distinct([bool equals(R previous, R next)?]) → Stream<R>: 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<R>: Returns the value of the indexth data event of this stream.
inherited
every(bool test(R element)) → Future<bool>: Checks whether test accepts all elements provided by this stream.
inherited
expand<S>(Iterable<S> convert(R element)) → Stream<S>: Transforms each element of this stream into a sequence of elements.
inherited
firstWhere(bool test(R element), {R orElse()?}) → Future<R>: Finds the first element of this stream matching test.
inherited
fold<S>(S initialValue, S combine(S previous, R element)) → Future<S>: Combines a sequence of values by repeatedly applying combine.
inherited
forEach(void action(R element)) → Future<void>: Executes action on each element of this stream.
inherited
handleError(Function onError, {bool test(dynamic error)?}) → Stream<R>: 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(R element), {R orElse()?}) → Future<R>: Finds the last element in this stream matching test.
inherited
listen(void onData(R value)?, {Function? onError, void onDone()?, bool? cancelOnError}) → StreamSubscription<R>: Adds a subscription to this stream.
inherited
map<S>(S convert(R event)) → Stream<S>: Transforms each element of this stream into a new stream event.
inherited
noSuchMethod(Invocation invocation) → dynamic: Invoked when a nonexistent method or property is accessed.
inherited
pipe(StreamConsumer<R> streamConsumer) → Future: Pipes the events of this stream into streamConsumer.
inherited
reduce(R combine(R previous, R element)) → Future<R>: Combines a sequence of values by repeatedly applying combine.
inherited
singleWhere(bool test(R element), {R orElse()?}) → Future<R>: Finds the single element in this stream matching test.
inherited
skip(int count) → Stream<R>: Skips the first count data events from this stream.
inherited
skipWhile(bool test(R element)) → Stream<R>: Skip data events from this stream while they are matched by test.
inherited
take(int count) → Stream<R>: Provides at most the first count data events of this stream.
inherited
takeWhile(bool test(R element)) → Stream<R>: Forwards data events while test is successful.
inherited
timeout(Duration timeLimit, {void onTimeout(EventSink<R> sink)?}) → Stream<R>: Creates a new stream with the same events as this stream.
inherited
toList() → Future<List<R>>: Collects all elements of this stream in a List.
inherited
toSet() → Future<Set<R>>: Collects the data of this stream in a Set.
inherited
toString() → String: A string representation of this object.
inherited
transform<S>(StreamTransformer<R, S> streamTransformer) → Stream<S>: Applies streamTransformer to this stream.
inherited
where(bool test(R event)) → Stream<R>: Creates a new stream from this stream that discards some elements.
inherited

Operators

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

Static Methods

join2<A, B, R>(Stream<A> streamOne, Stream streamTwo, R combiner(A a, B b)) → ForkJoinStream<dynamic, R>: Constructs a Stream that awaits the last values the provided Streams, then calls the combiner to emit an event of type R. After this event, the Stream closes.
join3<A, B, C, R>(Stream<A> streamA, Stream streamB, Stream<C> streamC, R combiner(A a, B b, C c)) → ForkJoinStream<dynamic, R>: Constructs a Stream that awaits the last values the provided Streams, then calls the combiner to emit an event of type R. After this event, the Stream closes.
join4<A, B, C, D, R>(Stream<A> streamA, Stream streamB, Stream<C> streamC, Stream<D> streamD, R combiner(A a, B b, C c, D d)) → ForkJoinStream<dynamic, R>: Constructs a Stream that awaits the last values the provided Streams, then calls the combiner to emit an event of type R. After this event, the Stream closes.
join5<A, B, C, D, E, R>(Stream<A> streamA, Stream streamB, Stream<C> streamC, Stream<D> streamD, Stream<E> streamE, R combiner(A a, B b, C c, D d, E e)) → ForkJoinStream<dynamic, R>: Constructs a Stream that awaits the last values the provided Streams, then calls the combiner to emit an event of type R. After this event, the Stream closes.
join6<A, B, C, D, E, F, R>(Stream<A> streamA, Stream streamB, Stream<C> streamC, Stream<D> streamD, Stream<E> streamE, Stream<F> streamF, R combiner(A a, B b, C c, D d, E e, F f)) → ForkJoinStream<dynamic, R>: Constructs a Stream that awaits the last values the provided Streams, then calls the combiner to emit an event of type R. After this event, the Stream closes.
join7<A, B, C, D, E, F, G, R>(Stream<A> streamA, Stream streamB, Stream<C> streamC, Stream<D> streamD, Stream<E> streamE, Stream<F> streamF, Stream<G> streamG, R combiner(A a, B b, C c, D d, E e, F f, G g)) → ForkJoinStream<dynamic, R>: Constructs a Stream that awaits the last values the provided Streams, then calls the combiner to emit an event of type R. After this event, the Stream closes.
join8<A, B, C, D, E, F, G, H, R>(Stream<A> streamA, Stream streamB, Stream<C> streamC, Stream<D> streamD, Stream<E> streamE, Stream<F> streamF, Stream<G> streamG, Stream<H> streamH, R combiner(A a, B b, C c, D d, E e, F f, G g, H h)) → ForkJoinStream<dynamic, R>: Constructs a Stream that awaits the last values the provided Streams, then calls the combiner to emit an event of type R. After this event, the Stream closes.
join9<A, B, C, D, E, F, G, H, I, R>(Stream<A> streamA, Stream streamB, Stream<C> streamC, Stream<D> streamD, Stream<E> streamE, Stream<F> streamF, Stream<G> streamG, Stream<H> streamH, Stream streamI, R combiner(A a, B b, C c, D d, E e, F f, G g, H h, I i)) → ForkJoinStream<dynamic, R>: Constructs a Stream that awaits the last values the provided Streams, then calls the combiner to emit an event of type R. After this event, the Stream closes.
list<T>(Iterable<Stream<T>> streams) → ForkJoinStream<T, List<T>>: Constructs a Stream that awaits the last values of the Streams in streams and then emits these values as a List. After this event, the Stream closes.