Example for CollectionView's didSelectItemAt with single selection

CollectionViewdidSelectItemAt.swift

func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath){
    // First selection, just set it and reload that cell
    guard let selectedIndexPath = selectedIndexPath else {
        selectedIndexPath = indexPath
        collectionView.reloadItems(at: [indexPath])
        return
    }
    // Reset to none selected and reload that cell
    if(selectedIndexPath == indexPath) {
        selectedIndexPath = nil
        collectionView.reloadItems(at: [indexPath])
    }
    // Set the new selected index and reload the previous and new cells.
    else {
        let indexPathsToRefresh = [indexPath, selectedIndexPath]
        selectedIndexPath = indexPath
        collectionView.reloadItems(at: [indexPathsToRefresh])
    }
}