hasEventListener method
Returns true if the EventDispatcher has event listeners. The
useCapture
paramenter defines if the event listeners should be
registered for the capturing event phase or not.
Implementation
bool hasEventListener(String eventType, {bool useCapture = false}) {
final eventStream = _eventStreams[eventType];
if (eventStream == null) return false;
return useCapture
? eventStream.hasCapturingSubscriptions
: eventStream.hasBubblingSubscriptions;
}