make superview respond to subView's UIPanGesture in some cases

Question

I have a scrollView and it contains a subView. SubView has a panGesture added to it.

What I want:

I need pangesture to work on subview only if the panning is done vertically. If the panning happens horizontally, I want the scrollView to respond for the panning instead of subview. How can I acheive this

Note: Iam able to find programatically when the panning happens horizontally.

Answer 1

There are several ways to do this:

1. Depending on what your subview does, you maybe able to replace it with a scrollview and lock it to scroll only vertically. (while the super should scroll only horizontally).
2. You can try feeding the touch information from the subview to it's superview if the pan gesture is moving horizontally. You could do this using a delegate pattern or, if you know what you're superview is, just access superview in your subview. However, this creates a strong coupling between the two views and probably shouldn't be done. It would be fragile and many would consider it code smell.
3. (best option) - Subclass UIGestureRecognizer and create your own gesture recognizer that only recognizes vertical movement. Use that instead of the UIPanGestureRecognizer.

Option 3 is the best, but probably the most work. You'll want to read Apple's docs on subclassing UIGestureRecognizer: Apple Docs - UIGestureRecognizer.

I've also written my own drag gesture recognizer, FlxDragGestureRecognizer.m, FlxDragGestureRecognizer.h (similar to a pan gesture recognizer), which you can use if you'd like, or take a look at to get a good idea of how to subclass UIGestureRecognizer. You can use this class to recognize touches moving only in certain directions, otherwise it will fail (which will allow other gesture recognizer to recognizer, like the scrollview). It also has a lot of other customizations and information it gathers, like velocity.

Answer 2

Since you already know how to detect the panning, then in you will need to implement a delegate protocol in your superview, a delegate property in your subview and assign your superview as a delegate for your subview.

when detecting horizontal panning, call the delegate method, when detecting vertical panning, implement what you want in the subview.