On 18 Oct 2008, at 6:45 am, Michael Ash wrote:
- (IBAction)sliderMoved:(id)sender {
SEL trackingEndedSelector = @selector(sliderEnded:);
[NSObject cancelPreviousPerformRequestsWithTarget:self
selector:trackingEndedSelector object:sender];
[self performSelector:trackingEndedSelector withObject:sender
afterDelay:0.0];
// do whatever you want to do during tracking here
}
- (void)sliderEnded:(id)sender {
// do whatever you want to do when tracking ends here
}
It may not be immediately obvious why this works. Delayed performs
happen in the default runloop mode (unless you specify otherwise using
the variant that has modes: at the end). Event tracking happens in a
special event tracking runloop mode. So the delayed perform won't
happen until the user lets go of the mouse button.
To keep these delayed performs from piling up, this method first
cancels any previous ones before scheduling the new one. An alternate
method would be to have some sort of flag that guarantees you only
schedule one, but this way is simpler and doesn't require a flag.
Reminds me of using a retriggerable monostable in hardware back in the
day (that day being before even embedded micros became common) ;-)
--Graham
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