Nested UITableViews: a way to scroll both the outer vertical UITableView and a child horizontal UITableView at the same time?

When you're working with an atypical nested UITableViews setup - where you have an outer vertical UITableView that hosts 90° rotated UITableViews (see: Looking for a UI library to present Data horizontaly in iOS ): is there a way to make iOS process vertical and horizontal touches at the same time?

I found that iOS is very clever in processing touches: horizontal touches make the relevant horizontal UITableView scroll, while a vertical swipe makes the outer UITableView scroll. Perfect.

Only, I'd love to be able to move my finger diagonally and see the outer UITableView and the inner UITableView scroll at the same time.

I tried a few approaches (playing with canCancelContentTouches, delaysContentTouches, and touch messages) but I haven't found a w开发者_高级运维ay to make this happen.

EDIT: Here's a XCode4 project that shows this behavior: http://marcanton.io/other/stackoverflow/nestedtableviews.zip

EDIT: I submitted this issue to Apple Developer Technical Support, here's their reply:

Thank you for writing to Apple Worldwide Developer Technical Support. I am responding to your inquiry concerning touch events in embedded UITableViews.

Typically this is an approach that is not recommended. The issue is that UITableView inherits from UIScrollView and as stated in the documentation for UIScrollView:

"Important: You should not embed UIWebView or UITableView objects in UIScrollView objects. If you do so, unexpected behavior can result because touch events for the two objects can be mixed up and wrongly handled."

http://developer.apple.com/library/ios/#documentation/UIKit/Reference/UIScrollView_Class/Reference/UIScrollView.html%23//apple_ref/occ/cl/UIScrollView

So that this time, there is not a workaround for getting both to scroll at the same time.

I recommend that you file an enhancement request at http://developer.apple.com/bugreporter/ detailing what you would like to see us add in a future release.

Still, I think that there has to be a way to enable this functionality, although I understand that this is not recommended. In fact, Apple does not even recommend hosting UITableViews inside another UITableView, but with the exception made above, it works quite beautifully. I'll keep this question updated with our collective findings.

EDIT: There actually is a way, detailed here: http://marcanton.io/blog/nested-orthogonal-tableviews/

This would have to be a custom mirroring of intercepted touch events. Touch events follow the responder chain model, which means that if an object in the responder chain (the top most (outermost) view) cannot handle the event or action, it resends the message to the next responder (in this case the background UITableView in the chain). This is why you are seeing the horizontal events go to the horizontal UITableView and the vertical events going to the vertical UITableView. A diagonal touch event has applicable horizontal and vertical events, so the top-most view (the outer vertical UITableView) can respond to the vertical touches and swallows the event.

If you think about it, all vertical touches likely have a little bit of horizontal events (think about when you flick your finger), so there is likely some work done in the background to determine how to interpret the touch event (either as a vertical or horizontal).

I found this tread on passing events down to the next object in the responder chain. You might want to give this a try as a partial solution to your puzzle. The rest is to figure out how to capture the horizontal touch events and pass them along to the next responder.

Interesting, I haven't played around with this kind of setup yet, but I would try to intercept touch events on the nested UITableViews and delegate any vertical movement to the outer UITableView - and vice-versa.