Question

I have a simple swipe gesture that I want to be very low priority. I want it to be cancelled by events that happen for controls on the view. At first, I thought this would be simple. It’s easy to cancel events when a gesture happens, but I can’t seem to do the opposite.

My solution is to cancel the gesture if it conflicts with any thing that is touchable. Here is the code I hacked together:

- (BOOL)gestureRecognizerShouldBegin:(UIGestureRecognizer *)gestureRecognizer
{
    CGPoint touch = [gestureRecognizer locationInView:self.view];
    return [self.view hitTest:touch withEvent:nil] == self.view;
}

I feel this is the wrong solution to the problem. What am I missing? What is the right way to get events to cancel gestures?

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For more context, I have two UISwipeGestureRecognizers (swipe left and swipe right) added to the view. There is also a UISlider in the view (part of an embedded MPVolumeView). When I moved the slider to change the volume, the left or right swipe would fire.

Answer 1

This is the correct way to do what you want. You are telling the gesture recognizer that it should only begin if the touch is directly in the view, not any subviews (according to hitTest: which is good because it allows the views to decide if they are hit or not).

It’s always better to prevent it from starting rather than trying to cancel it afterwards. However, if you do want to cancel the gesture after it has started, set enabled = NO and then back to YES again.

If you need to allow the gesture for some subviews but not controls you can test if the view returned by hitTest: is a subclass of UIControl (for example) using isKindOfClass:.

I don’t know what type of gesture this is for, but usually you don’t need to do this because UIKit will automatically find the deepest view that wants the touches and that view will ‘eat’ them so outer gesture recognizers won’t get them – however I can imagine this doesn’t hold true for some combinations of recognizer/control.