[iPhone SDK] Events Filtered: UIControl Subclass Inside a UITableViewCell

Question

I have a control derived from UIControl that needs to respond to drags, similar in some respects to a UISlider. Touch events are handled by implementations of touchesBegan:withEvent:, touchesMoved:withEvent:, touchesEnded:withEvent, and touchesCancelled:withEvent:. The control works very well, unless I make it a subview of a UITableViewCell. Once I do that, I'll get the touchesBegan:withEvent: call, but often no others. Thus, the control responds to an initial touch, but will not respond to drags. Even setting the exclusiveTouch property within the touchesBegan:withEvent: method doesn't help; the events are never reaching my code.
Interestingly, I can drop a UISlider in my table and it responds to touch events just fine. So obviously there's a way to get these events delivered... but I'm suspecting that the UIScrollView that UITableView inherits from is interfering with the delivery of the touch events. The reference for UIScrollView talks about how to override its event interception in subclasses, but if UISlider can get away without a special subclassed container, well, by golly, I'd like to do that, too.
This may have a simple solution ("hey Dave, just set this property"), but so far it's eluded me.
So, does anyone here understand UITableView mechanics enough to guess where the touch messages might be getting filtered, and how to tell the responsible class to knock it off? I will accept source code for UISlider as an answer.

Answer 1

Hello, there is a much better solution:
First let me explain what happens:
The UITableView extends from UIScrollView. UIScrollView intercepts all the events to make the decision if it is a scroll or not, if not it passes the event to the subviews. (Except when you have a UIslider)
The solution is to extend UITableView and override this method:
- (UIView *)hitTest:(CGPoint)point withEvent:(UIEvent *)event {
UIView *v = [self viewWithTag:999]; //999 is the tag of your subview, that you want to capture events
CGPoint convertedPoint = [self convertPoint:point toView:v];
// If the touch is inside the view, let the view handle it
if ([v pointInside:convertedPoint withEvent:event]) {
return v;
} else {
return [super hitTest:point withEvent:event];
When you Extend UISlider the hitTest returns the sliderview on a touch event but not when you extend UIControl. That I can not explain.
Overriding the hitTest you can test if the point argument is inside in your view (converting to its coordinates) and Return it the view like what happens in a UISlider.
If someone know why the UISlider is an exception in this hitTest method, please tell us.
Hope this helps you people, trying to capture touches in a UITableView or UIScrollView without the interference of the scrool detection.
Best regards, João
http://www.nanoappz.com/