How to receive touch event behind another view? - ios

Question

I have two subviews inside the view. The frame is equal. A view has a swipe left gesture recognizer and B view has a swipe right gesture recognizer. B is behind A so I can only trigger swipe left gesture. How can I receive both?

Answer 1

The view in the back will not respond because, well, it's in the back.
For both gestures to respond simultaneously (left+right at the same time), add a UIGestureRecognizerDelegate to either and handle shouldRecognizeSimultaneouslyWithGestureRecognizer as suggested below.
If you want B to respond to a gesture, even though it is partially hidden by A, rethink your hierarchy: add a 3rd view above A & B (call it C), same size as B, as a placeholder to your gesture recognizer.
Your delegate:
// leftGesture
- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer
shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer
*)otherGestureRecognizer
{
return otherGestureRecognizer == rightGesture;
}

Answer 2

How can I receive both?
Add both gesture recognizers to view A, since that's the view in front. Since you need the right swipe gesture to be handled by view B, make view B the target for the right swipe gesture recognizer.
A better option might be to make your view controller the target of both gesture recognizers and let it sort out what to do with the user's gestures. That helps to get the views out of the business of knowing how the user interface is set up -- they just have to follow instructions from the view controller. If you adopt that plan, your view controller might look like this in part:
- (void)viewDidLoad
{
UISwipeGestureController *leftSwipe = [[UISwipeGestureController alloc] initWithTarget:self action:#selector(leftSwipe:)];
leftSwipe.direction = UISwipeGestureRecognizerDirectionLeft;
UISwipeGestureController *rightSwipe = [[UISwipeGestureController alloc] initWithTarget:self action:#selector(rightSwipe:)];
rightSwipe.direction = UISwipeGestureRecognizerDirectionRight;
[self.viewA addGestureRecognizer:leftSwipe];
[self.viewA addGestureRecognizer:rightSwipe];
}
- (IBAction)leftSwipe:(id)sender
{
[self.viewA doSomething];
}
- (IBAction)rightSwipe:(id)sender
{
[self.viewB doSomethingElse];
}