Don't call didSelectItemAtIndexPath method

[akkie76]

Hi developers
The func collectionView (_ collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: IndexPath) method of DemoApp DemoViewController is not called, but how do you pick up the event of didSelectItemAtIndexPath.

extension ExpandingViewController: UICollectionViewDataSource, UICollectionViewDelegate {

    // Need to add method ??
    open func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
    }

}