Question

I have a overridden UIGestureRecogniser designed to detect 2 touches, but not necessarily one immediately after the other.

I have:

- (BOOL)canBePreventedByGestureRecognizer:(UIGestureRecognizer *)preventingGestureRecognizer
{
    if ([preventingGestureRecognizer isKindOfClass:[UIRotationGestureRecognizer class]])
    {
        self.state = UIGestureRecognizerStateCancelled;
        return YES;
    }

    if ([preventingGestureRecognizer isKindOfClass:[UISwipeGestureRecognizer class]])
    {
        self.state = UIGestureRecognizerStateCancelled;
        return YES;
    }

    //Will prevent a conflict with a 2 finger touch only.   
    if ([preventingGestureRecognizer isKindOfClass:[UITapGestureRecognizer class]])
    {
        if (preventingGestureRecognizer.numberOfTouches == 2)
        {
            self.state = UIGestureRecognizerStateCancelled;
            return YES;
        }  
        return NO;
    }
    self.state = UIGestureRecognizerStateRecognized;
    return NO;
}

In my MVC I also have a Rotation Gesture Recogniser. My problem is they are conflicting. my doubleTap gesture recogniser is calling its action @selector when It should be prevented by the above method.

It looks like the above method is not called. I think this is because when the two fingers touch to perform the rotation the following code:

- (void)secondTouchRecived
{
    self.state = UIGestureRecognizerStateRecognized;
}

calls the UIGestureResponders action method and by-passes the prevention method. Ive tried changing it to UIGestureRecogniserStateBegan but this too seems to by-passes the prevention method.

Answer 1

What about specifying a dependency by passing the rotation, swipe and tap gesture recognizers into requireGestureRecognizerToFail: on your custom gesture recognizer? That would prevent your gesture recognizer from transitioning to the Recognized state before the Rotation recognizer gets a chance to process the touches.