Gestures that steal touches like iOS multitasking swipe?

I would suggest you to try using method swizzling, reimplementing the touchesbegan on UIView. I think that the best way is to store in a static shared variable the number of touches (so that each view can increment/decrement this value). It's just a very simple idea, take it with a grain of salt.

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I know what I want to do, but I'm stumped as to how to do it: I want to implement something like the iOS multitasking gestures. That is, I want to "steal" touches from any view inside my view hierarchy if the number of touches is greater than, say, two. Of course, the gestures are not meant to control multitasking, it's just the transparent touch-stealing I'm after.

Since this is a fairly complex app (which makes extensive use of viewController containment), I want this to be transparent to the views that it happens to (i. E. I want to be able to display arbitrary views and hierarchies, including UIScrollViews, MKMapViews, UIWebViews etc. without having to change their implementation to play nice with my gestures).

Just adding a gestureRecognizer to the common superview doesn't work, as subviews that are interaction enabled eat all the touches that fall on them. Adding a visually transparent UI-enabled view as a sibling (but in front) of the main view hierarchy also doesn't work, since now this view eats all the touches. I've experimented with reimplementing touchesBegan: etc. in the touchView, but forwarding the touches to nextResponder doesn't work, because that'll be the common superview, in effect funnelling the touches right around the views that are supposed to be receiving them when the touchView gives them up.

I am sure I'm not the only one looking for a solution for this, and I'm sure there are smarter people than me that have this already figured out. I even suspect it might not actually be very hard, and just maybe my brain won't see the forest for the trees today. I'm thankful for any helpful answers anyway :) ios cocoa-touch uiview uigesturerecognizer link|improve this question asked Mar 16 at 18:52fzwo1,876415 80% accept rate.

I would suggest you to try using method swizzling, reimplementing the touchesbegan on UIView. I think that the best way is to store in a static shared variable the number of touches (so that each view can increment/decrement this value). It's just a very simple idea, take it with a grain of salt.

Hope this helps. Ciao! :).

A possible, but potentially dangerous (if you aren't careful) approach is to subclass your application UIWindow and redefine the sendEvent: method. As this method is called for each touch event received by the app, you can inspect it and then decide to call super sendEvent: (if the touch is not filtered), or don't' call it (if the touch is filtered) or just defer its call if you are still recognizing the touch. Another possibility is to play with the hitTest:withEvent: method but this would require your stealing view to be placed properly in the subview, and I think it doesn't fit well when you have many view controllers.

I believe the previous solution is more general purpose.

Actually, adding a gesture recognizer on the common superview is the right way to do this. But it sound like you may need to set either delaysTouchesBegan or cancelsTouchesInView (or both) to ensure that the gesture recognizer handles everything before letting it through to the child views.

That's what I tried, but zooming ScrollViews still steal the touches. – fzwo Mar 18 at 10:30.

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