My problem is really simple. I would like to animate a cell within a collectionView. Indeed, I would like to show a grey background behind the cell and scale down the image
You have several options.
You can implement the collection view delegate method collectionView(:didSelectItemAtIndexPath:)
and put your code there.
You can attach a tap gesture recognizer to your view that you want to respond to taps.
You Can create a custom button and install an image into it and then use the IBAction method of the button as normal.