Creates a stream that repeatedly emits events at period
intervals.
The event values are computed by invoking computation
. The argument to this callback is an integer that starts with 0 and is incremented for every event.
If computation
is omitted the event values will all be null
.
factory Stream.periodic(Duration period, [T computation(int computationCount)]) { Timer timer; int computationCount = 0; StreamController<T> controller; // Counts the time that the Stream was running (and not paused). Stopwatch watch = new Stopwatch(); void sendEvent() { watch.reset(); T data; if (computation != null) { try { data = computation(computationCount++); } catch (e, s) { controller.addError(e, s); return; } } controller.add(data); } void startPeriodicTimer() { assert(timer == null); timer = new Timer.periodic(period, (Timer timer) { sendEvent(); }); } controller = new StreamController<T>( sync: true, onListen: () { watch.start(); startPeriodicTimer(); }, onPause: () { timer.cancel(); timer = null; watch.stop(); }, onResume: () { assert(timer == null); Duration elapsed = watch.elapsed; watch.start(); timer = new Timer(period - elapsed, () { timer = null; startPeriodicTimer(); sendEvent(); }); }, onCancel: () { if (timer != null) timer.cancel(); timer = null; return Future._nullFuture; }); return controller.stream; }
© 2012 the Dart project authors
Licensed under the Creative Commons Attribution-ShareAlike License v4.0.
https://api.dartlang.org/stable/2.0.0/dart-async/Stream/Stream.periodic.html