UIPanGestureRecognizer sometimes not working on iOS 7

Question

I'm getting intermittent reports from users on iOS 7 saying that the UIPanGestureRecognizer stops working on certain views every once in a while. They're supposed to be able to swipe a view to the right/left, but it just breaks and doesn't work for some unknown reason. Force quitting the app and relaunching it fixes the problem.

This problem never happened on iOS 6. And I don't have any code that disables the gesture recognizer at any time besides the gestureRecognizerShouldBegin delegate that forces the gesture to only recognize horizontal pans:

- (BOOL)gestureRecognizerShouldBegin:(UIPanGestureRecognizer *)gestureRecognizer {

    if ([gestureRecognizer isMemberOfClass:[UIPanGestureRecognizer class]]) { 

        CGPoint translation = [gestureRecognizer translationInView:[self superview]];

        if (fabsf(translation.x) > fabsf(translation.y)) {

            if (translation.x > 0)
                return YES;
        }
    }
    return NO;
}

Did anything change in the UIPanGestureRecognizer (or just the plain UIGestureRecognizer) that could be causing this problem?

Answer 1

I think I finally solved this issue. Apparently iOS 7 handles gestures in subviews differently than it did in iOS 6 and earlier. To handle this, Apple implemented a new delegate:

(BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldBeRequiredToFailByGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer

If you return YES, that should get your gesture recognizer to work. I've implemented it and haven't had any issues so far (though admittedly this was a rare bug that I could never reliably reproduce, so it's possible that it just hasn't recurred yet).

For more information, see https://stackoverflow.com/a/19892166/1593765.