UIGestureRecognizerDelegateExample.m

- (BOOL)gestureRecognizerShouldBegin:(UIPanGestureRecognizer *)recognizer {
    if (recognizer != self.panGestureRecognizer) {
        if ([super respondsToSelector:@selector(gestureRecognizerShouldBegin:)]) {
            return [super gestureRecognizerShouldBegin:recognizer];
        } else {
            return YES;
        }
    }

    CGPoint translation = [recognizer translationInView:self];
    // Fail vertical swipes.
    return (abs(translation.y) < abs(translation.x));
}