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.


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

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


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


done Future
A future which is completed when the stream controller is done sending events.
no setteroverride
hashCode int
The hash code for this object.
no setterinherited
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 setterinherited
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


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


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