How to add tap gesture to UICollectionView , while maintaining cell selection?

Question

Task

Add a single tap gesture to UICollectionView, do not get in the way of cell selection.

I want some other taps on the no-cell part of the collectionView.

Code

Using XCode8, Swift 3.

override func viewDidLoad() {
    ...
    collectionView.addGestureRecognizer(UITapGestureRecognizer(target: self, action: #selector(tap)))
}

func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
    print(indexPath)
}

func tap(sender: UITapGestureRecognizer){
    print("tapped")
}

Result

Yeah, it gets in the way now. When you tap on cell, it logs "tapped".

Analysis

• I check the hitTest return value of the collectionView and the cell. Both returned the tapped cell, which means they form a responder chain of Cell -> CollectionView
• no gestures on the cell
• 3 gestures on collectionView, no one seems to work with the cell select
  • UIScrollViewDelayedTouchesBeganGestureRecognizer
  • UIScrollViewPanGestureRecognizer
  • UITapGestureRecognizer
• callStack, seems cell selection has a different stack trace with gesture's target-action pattern.
• double tap gesture works along with cell selection.

Question

Couldn't find more trace. Any ideas on how cell selection is implemented or to achieve this task?

Solution 1

Whenever you want to add a gesture recognizer, but not steal the touches from the target view, you should set UIGestureRecognizer.cancelsTouchesInView for your gestureRecognizer instance to false.

Solution 2

Instead of trying to force didSelectItem you can just get the indexPath and/or cell this way:

func tap(sender: UITapGestureRecognizer){

    if let indexPath = self.collectionView?.indexPathForItem(at: sender.location(in: self.collectionView)) {
        let cell = self.collectionView?.cellForItem(at: indexPath)
        print("you can do something with the cell or index path here")
    } else {
        print("collection view was tapped")
    }
}

Comments

[jchnxu]

Thanks! I returned to the basic docs again and try to find anything I miss!

[jchnxu]

Thanks! This is really helpful. I'm going to add more gestures to the collectionView. Seems like UICollectionView is analysing raw touches rather than using a high level gesture recogniser, and that's limited.