showCellDetail.swift

    @IBSegueAction func showDetail(_ coder: NSCoder) -> UIViewController? {
//        guard let item = collectionView.indexPathsForSelectedItems else { return nil }
        //利用indexPathsForSelectedItems?.first?.item(row)來對應要顯示的物件
        guard let item = collectionView.indexPathsForSelectedItems?.first?.item else { return nil }
        let controller = DetailViewController(coder: coder)
        controller?.imageName = photos[item]
        return controller
    }