GalleriViewController.swift

func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        let photo = photos[indexPath.row]
        print("photogg:\(photo)")
        showPhotoDetail(photo: photo)
    }
    
    func showPhotoDetail(photo: Photo) {
        let vc: GalleryDetailViewController = UIViewController.instantiateViewController(storyBoard: "Gallery", identifier: "galleryDetailViewController") as! GalleryDetailViewController
        vc.photo = photo
        self.navigationController?.pushViewController(vc, animated: false)
    }