Forward/pass through UIGesture (swipe) to sibling view

Question

Let's assume the following setup:

There is a horizontal-only scrolling, transparent UIScrollView(rectangle with blueish background and red border) and a infinite number of UIImageView instances (reddish squares) being subviews of the same UIView (self.view).

The UIScrollView is being brought to front by

[self.view bringSubviewToFront:scrollView]

in the containing UIViewController.

The following shall be achieved: The UIScrollView should receive the left/right swipe gestures to scroll horizontally, whereas the UIImageViews covert by the UIScrollView should receive swipe gestures with direction up/down, which are added as follows:

UISwipeGestureRecognizer *swipeGesture = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:@selector(swipeUpGestureHandler:)];
swipeUpGesture.direction = UISwipeGestureRecognizerDirectionUp | UISwipeGestureRecognizerDirectionDown;
[imageView addGestureRecognizer:swipeGesture];

This works when the UIImageView is not covered by the UIScrollView, but obviously does not work when the UIScrollView is in front of said views.

To summarize, the UIScrollView should forward the up/down swipe event / gesture to the specific underlying UIImageView, but still receive the regular left/right swipe event / gesture for horizontal scrolling.

From what I read in the documentation it would be easy to solve if the UIImageViews would be contained inside the UIScrollView - however, that is not possible in this setup, and I'm pretty sure there has to be a solution to solve this problem.

Any hints are appreciated, thank you.

Answer 1

I've found a solution for this issue. While I was unable to forward the swipe up/down gestures to the image views behind the scrollview, I've now added gesture recognisers with direction up/down to the scrollview. In the gesture recognisers actions, I determine the point of the gesture within the window and hittest the window's first view for these point with a nil event. In the custom scrollview, I overwrote the hittest message to return NO with an empty event so the appropriate imageview would eventually be identifier. Once I got the imageview lying behind the scrollview at the point of the gesture, I was able to perform the appropriate action on my imageview.

I'm not sure whether this is the finest solution for this issue, however I wasn't able to build a better one after hours of investigation and experimenting. This setup might be a bit unusual and therefor tricky. Your input is still appreciated in case you have anything to add.