如果将轻按手势识别器添加到其背景视图，则不会调用iOS didSelectItemAtIndexPath

Question

I have a UIView A, and I added a UICollectionView B to A as a subView, so now view A is B's background view. Here didSelectItemAtIndexPath will get called normally at this time. But if I add a tap gesture recognizer to View A, then didSelectItemAtIndexPath won't be called. The code is simple like below

UITapGestureRecognizer *tap2 = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(tap2)];
[viewA addGestureRecognizer:tap2];

How can I make didSelectItemAtIndexPath get called for this situation? My expected behavior is both tapping cell and tapping background methods get called normally and separately as they have different tap behaviors.

Answer 1

From Apple's documentation:

You should always attach your gesture recognizers to the collection view itself—not to a specific cell or view. The UICollectionView class is a descendant of UIScrollView, so attaching your gesture recognizers to the collection view is less likely to interfere with the other gestures that must be tracked. In addition, because the collection view has access to your data source and your layout object, you still have access to all the information you need to manipulate cells and views appropriately.

https://developer.apple.com/library/content/documentation/WindowsViews/Conceptual/CollectionViewPGforIOS/IncorporatingGestureSupport/IncorporatingGestureSupport.html

I have done this and it works very well. Generally I would call indexPathForItemAtPoint: on the collectionView to get the indexPath and then get the cell from cellForItemAtIndexPath . In your case you can check to see that indexPathForItemAtPoint returns nil (ie the user is clicking on an area between the cells) and then do your code for that. You can also use UIView convertRect methods to figure out exactly where the touch it.