description

# StreamController<T> class abstract interface

A controller with the stream it controls.

This controller allows sending data, error and done events on its stream.

This class can be used to create a simple stream that others can listen on, and to push events to that stream.

It's possible to check whether the stream is paused or not, and whether it has subscribers or not, as well as getting a callback when either of these change.

Example:

    final streamController = StreamController(
      onPause: () => print('Paused'),
      onResume: () => print('Resumed'),
      onCancel: () => print('Cancelled'),
      onListen: () => print('Listens'),
    );

    streamController.stream.listen(
      (event) => print('Event: $event'),
      onDone: () => print('Done'),
      onError: (error) => print(error),
    );

To check whether there is a subscriber on the stream, use hasListener.

    var hasListener = streamController.hasListener; // true

To send data events to the stream, use add or addStream.

    streamController.add(999);
    final stream = Stream<int>.periodic(
        const Duration(milliseconds: 200), (count) => count * count).take(4);
    await streamController.addStream(stream);

To send an error event to the stream, use addError or addStream.

    streamController.addError(Exception('Issue 101'));
    await streamController.addStream(Stream.error(Exception('Issue 404')));

To check whether the stream is closed, use isClosed.

    var isClosed = streamController.isClosed; // false

To close the stream, use close.

    await streamController.close();
    isClosed = streamController.isClosed; // true

Implemented types
  - StreamSink<T>
Implementers
  - MultiStreamController
  - SynchronousStreamController

## Constructors

StreamController({void onListen()?, void onPause()?, void onResume()?, FutureOr<void> onCancel()?, bool sync = false})
  A controller with a stream that supports only one single subscriber.
  factory
StreamController.broadcast({void onListen()?, void onCancel()?, bool sync = false})
  A controller where stream can be listened to more than once.
  factory

## Properties

done → Future
  A future which is completed when the stream controller is done sending events.
  no setter override
hashCode → int
  The hash code for this object.
  no setter inherited
hasListener → bool
  Whether there is a subscriber on the Stream.
  no setter
isClosed → bool
  Whether the stream controller is closed for adding more events.
  no setter
isPaused → bool
  Whether the subscription would need to buffer events.
  no setter
onCancel ↔ FutureOr<void> Function()?
  The callback which is called when the stream is canceled.
  getter/setter pair
onListen ↔ void Function()?
  The callback which is called when the stream is listened to.
  getter/setter pair
onPause ↔ void Function()?
  The callback which is called when the stream is paused.
  getter/setter pair
onResume ↔ void Function()?
  The callback which is called when the stream is resumed.
  getter/setter pair
runtimeType → Type
  A representation of the runtime type of the object.
  no setter inherited
sink → StreamSink<T>
  Returns a view of this object that only exposes the StreamSink interface.
  no setter
stream → Stream<T>
  The stream that this controller is controlling.
  no setter

## Methods

add(T event) → void
  Sends a data `event`.
  override
addError(Object error, [StackTrace? stackTrace]) → void
  Sends or enqueues an error event.
  override
addStream(Stream<T> source, {bool? cancelOnError}) → Future
  Receives events from `source` and puts them into this controller's stream.
  override
close() → Future
  Closes the stream.
  override
noSuchMethod(Invocation invocation) → dynamic
  Invoked when a nonexistent method or property is accessed.
  inherited
toString() → String
  A string representation of this object.
  inherited

## Operators

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