cancel method
Cancel the event subscription with the subject. Eventhough the cancel method is called, listener doesn't check the cancellation of the subscription. Subscription cancellation shall be implemented in the _cancelCallback function. The Default constructor doesn't provide a mechanism to cancel the subscription. Use the EventEmitter.on to cancel the suscrition effectively. Returns true, if _cancelCallback is successfully executed, false otherwise.
Implementation
bool cancel() {
if (null != _cancelCallback) {
_cancelCallback!();
return true;
}
return false;
}