abstract class StreamController<T>

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.

If the stream starts or stops having listeners (first listener subscribing, last listener unsubscribing), the onSubscriptionStateChange callback is notified as soon as possible. If the subscription stat changes during an event firing or a callback being executed, the change will not be reported until the current event or callback has finished. If the pause state has also changed during an event or callback, only the subscription state callback is notified.

If the subscriber state has not changed, but the pause state has, the onPauseStateChange callback is notified as soon as possible, after firing a current event or completing another callback. This happens if the stream is not paused, and a listener pauses it, or if the stream has been resumed from pause and has no pending events. If the listeners resume a paused stream while it still has queued events, the controller will still consider the stream paused until all queued events have been dispatched.

Whether to invoke a callback depends only on the state before and after a stream action, for example firing an event. If the state changes multiple times during the action, and then ends up in the same state as before, no callback is performed.

If listeners are added after the stream has completed (sent a "done" event), the listeners will be sent a "done" event eventually, but they won't affect the stream at all, and won't trigger callbacks. From the controller's point of view, the stream is completely inert when has completed.