asBroadcastStream method
- void onListen(
- StreamSubscription<
Uint8List> subscription
- StreamSubscription<
- void onCancel(
- StreamSubscription<
Uint8List> subscription
- StreamSubscription<
Returns a multi-subscription stream that produces the same events as this.
The returned stream will subscribe to this stream when its first subscriber is added, and will stay subscribed until this stream ends, or a callback cancels the subscription.
If onListen
is provided, it is called with a subscription-like object
that represents the underlying subscription to this stream. It is
possible to pause, resume or cancel the subscription during the call
to onListen
. It is not possible to change the event handlers, including
using StreamSubscription.asFuture.
If onCancel
is provided, it is called in a similar way to onListen
when the returned stream stops having listeners. If it later gets
a new listener, the onListen
function is called again.
Use the callbacks, for example, for pausing the underlying subscription while having no subscribers to prevent losing events, or canceling the subscription when there are no listeners.
Cancelling is intended to be used when there are no current subscribers.
If the subscription passed to onListen
or onCancel
is cancelled,
then no further events are ever emitted by current subscriptions on
the returned broadcast stream, not even a done event.
Example:
final stream =
Stream<int>.periodic(const Duration(seconds: 1), (count) => count)
.take(10);
final broadcastStream = stream.asBroadcastStream(
onCancel: (controller) {
print('Stream paused');
controller.pause();
},
onListen: (controller) async {
if (controller.isPaused) {
print('Stream resumed');
controller.resume();
}
},
);
final oddNumberStream = broadcastStream.where((event) => event.isOdd);
final oddNumberListener = oddNumberStream.listen(
(event) {
print('Odd: $event');
},
onDone: () => print('Done'),
);
final evenNumberStream = broadcastStream.where((event) => event.isEven);
final evenNumberListener = evenNumberStream.listen((event) {
print('Even: $event');
}, onDone: () => print('Done'));
await Future.delayed(const Duration(milliseconds: 3500)); // 3.5 second
// Outputs:
// Even: 0
// Odd: 1
// Even: 2
oddNumberListener.cancel(); // Nothing printed.
evenNumberListener.cancel(); // "Stream paused"
await Future.delayed(const Duration(seconds: 2));
print(await broadcastStream.first); // "Stream resumed"
// Outputs:
// 3
Implementation
@override
Stream<T> asBroadcastStream({
void Function(StreamSubscription<T> subscription)? onListen,
void Function(StreamSubscription<T> subscription)? onCancel,
}) =>
stream.asBroadcastStream(onListen: onListen, onCancel: onCancel);