StreamController<T> class Null safety

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