didDeselectItemAt For UIcollectionView is not called but didSelectItemAt is called? - swift

Question

I am trying to implement a multi selection for UICollectionView. The delegate function didSelectItemAt is called but didDeselectItemAt is NEVER called and I do not know why? I am not even sure how it works. If I click on a cell - didSelectItemAt is called. So if I click once again on the same cell is didDeselectItemAt supposed to be called?
My UIViewController inherits and conforms to all of the following: UICollectionViewDelegate ,UICollectionViewDataSource, UICollectionViewDelegateFlowLayout
viewdidLoad():
collectionView.allowsSelection = true
collectionView.allowsMultipleSelection = true
Delegate functions:
override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
print("didSelectItemAt")
}
func collectionView(_ collectionView: UICollectionView, didDeselectItemAt indexPath: IndexPath) {
print("DESELECT")
}

Answer 1

Please see this open issue on Github.
It could be that you have a tap gesture recognizer on a view in the same hierarchy that contains your collection view. Remove the tap gesture and see if that works. This happened to be my issue.
let tap = UITapGestureRecognizer(...) // your tap gesture recognizer
view.addGestureRecognizer(tap) // what you already have
tap.cancelsTouchesInView = false

Answer 2

I'm going to guess that your code is different from what you have shown us, and in that in your real code, you have not given the correct signature for didDeselect. Here's why. Look carefully at the code you have shown:
override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
print("didSelectItemAt")
}
func collectionView(_ collectionView: UICollectionView, didDeselectItemAt indexPath: IndexPath) {
print("DESELECT")
}
Now ask yourself: Why did the compiler permit the second func to stand, even though you forgot to say override? I'm guessing it's because it is not an override. There is something wrong with the signature, so it's just a meaningless function that doesn't conform to UICollectionViewDelegate.
Try using code completion to re-enter this function. If all goes well, it will be an override and it will start working.
To illustrate more precisely: This compiles, but the second method will never be called:
class CV : UICollectionViewController {
override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
print("didSelectItemAt")
}
func colectionView(_ collectionView: UICollectionView, didDeselectItemAt indexPath: IndexPath) {
print("DESELECT")
}
}
But this doesn't compile, because the signature is correct but we forgot override:
class CV : UICollectionViewController {
override func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
print("didSelectItemAt")
}
func collectionView(_ collectionView: UICollectionView, didDeselectItemAt indexPath: IndexPath) {
print("DESELECT")
}
}
But in that second one, if we do say override, it compiles and works.

Answer 3

It works like this:
if collectionView.allowsMultipleSelection = false // default then you have to tap on a different cell in order to deselect the previous one.
if collectionView.allowsMultipleSelection = true // only tapping on the same cell triggers deselect delegate method

Answer 4

I'm not sure if this changed recently, but with iOS13 it seems that simply specifying that a collection view cell is selected when the cell is dequeued is not enough for the collection view to allow you to deselect the cell. You need to also manually tell the collection view to select the cell.
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: photoCellIdentifier, for: indexPath) as! YourCell
cell.isSelected = true
if cell.isSelected {
collectionView.selectItem(at: indexPath, animated: false, scrollPosition: .left)
}
}
I figured this out because i was able to select and deselect cells, but was not able to deselect a cell that was initially selected.