Hi

I'm doing Project 7 of Hacking with macOS and did the performExternalDrag function and there aren't any errors showing in Xcode, but when I run the app and try to drag a file from Finder into the app window, it shows the blue insertion line but when I release the mouse button, nothing happens. I've checked my code against the project files and it looks correct. Here's my code:

    func performExternalDrag(with items: [NSPasteboardItem], at indexPath: IndexPath) {
        let fm = FileManager.default

        // 1. loop over every item on the drag and drop pasteboard
        for item in items {
            // 2. pull out the string containing the URL for this item
            guard let stringURL = item.string(forType: NSPasteboard.PasteboardType(kUTTypeURL
                as String)) else { continue }

            // 3. attempt to convert the string into a real URL
            guard let sourceURL = URL(string: stringURL) else { continue }

            // 4. create a destination URL by combining 'photosDirectory' with the last path component
            let destinationURL =
                photosDirectory.appendingPathComponent(sourceURL.lastPathComponent)

            do {
                // 5. attempt to copy the file to our app's folder
                try fm.copyItem(at: sourceURL, to: destinationURL)
            } catch {
                print("Error copying item from: \(sourceURL): \(error)")
                continue
            }

            // 6. update the array and collection view
            photos.insert(destinationURL, at: indexPath.item)
            collectionView.insertItems(at: [indexPath])

        }

    }

Any ideas what I missed?