attachCancellable method
Attaches a Cancellable
to this token.
Before attaching to a CancellationToken, you should check if it's already been cancelled by using isCancelled.
Implementation
@override
void attachCancellable(Cancellable cancellable) {
if (!isCancelled && _timer == null) Timer(_duration, _onTimerEnd);
super.attachCancellable(cancellable);
}