Detect ANY touch in the view (iPhone SDK)

Question

I am currently using ...

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event { - (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event { - (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event { 

for spot detection. Everything works. The only problem is that the user is touching something (e.g., UIButton or something else) - (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event { not called. Is there something like touchhesBegan but will work if I touch ANY looking?

Thanks in advance, David

Answer 1

Touch events are propagated as follows:

• UIViews is sent -hitTest: withEvent: recursively, until some UIView decides that the touch is inside its borders, and not inside any subtitle with user interaction enabled.
• UIWindow sends -touchesBegan: withEvent: and the friends in the UIView returned in step 1, ignoring any view hierarchy.

In other words, -hitTest: withEvent: is used to determine the target view to touch, after which the target view receives all -touches ...: withEvent: messages. If you need to intercept a gesture of gestures that can start in UIButton, you will have to override -hitTest: withEvent: to return self.

But there is a problem with this approach. Once you do this, your button will stop working because it will not receive any -touches ...: withEvent: messages. You will have to redirect the touch to sub-items manually if you do not find a swipe with a gesture. This is a serious pain in the butt and work is not guaranteed at all. What are UIGestureRecognizers intended for?

Another approach is to subclass UIWindow and override -sendEvent:, which might work better in your case.

In any case, be sure to carefully read the Event Handling documentation. Other scary warnings say:

The UIKit structure classes are not intended to receive strokes that are not related to them; in software terms, this means that the presentation property of a UITouch object must reference the structure of the object in order for the touch to be processed.

Answer 2

I think you should have one or the other. Do you want the iPhone to detect a touch on top of a button or a touch on top of a view? I do not think that you can do both at the same time, and I would be surprised if I could. Sorry for not having a better answer ...