How to get a UIView under a UIScrollView to detect touches?

Question

I have a UIScrollView ontop of my UIViewController recreating an effect like in the Gowalla iPhone app when you're on a spot's page. Under my scroll view I have a button that I want to be able to perform it's action even when the scroll view's frame covers it up (where it's ontop of the button, the scroll view's clear). How would I do something like this? Is it possible? (it has to be, Gowalla [somehow] did it)

Answer 1

As for me, I will transfer touch event to another view by override following methods.

• – touchesBegan:withEvent:
• – touchesMoved:withEvent:
• – touchesEnded:withEvent:
• – touchesCancelled:withEvent:

Like this way,

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
     // pass touch event by default implement.
     [super touchesBegan:touches withEvent:event]; 

     // redirect the touch events. 
     [anotherView touchesBegain:touches withEvent:event];    
}

hitTest:withEvent: is used to decide which view should response touch event on the view hierarchy tree. If the view doesn't want to response touch event, it will return nil in hitTest. As result the above touch event methods won't be called.

Answer 2

I have no idea what this "Gowalla" app might do; hopefully, your description of "a button behind the scroll view, that you can touch 'through' the scroll view" is accurate.

If your button behind the scroll view can be sized to fill the entire contentSize area of the scroll view without screwing up your interface, the easiest solution would be to just put it inside the scroll view (under all the other views) and do just that.

Otherwise, your best bet is probably to create a custom view with a clear background to be placed in the scroll view as above. The easy solution is to have the custom view (probably a UIControl) just do whatever touching the button does. If that's not possible for some reason, your best option would be to override hitTest:withEvent: on the custom view to return the underlying button. I'd be wary of overriding hitTest:withEvent: on the scroll view itself, as that might interfere with scrolling.

Answer 3

Try adding the button on top of the scroll view. The only problem with that is if you hit the button, you will not be able to interact with the scrollView, but it will still be visible.