Drag and drop with custom type identifier doesn't work

Question

I'm trying to achieve drag and drop on macOS with a custom type identifier to avoid collisions but it doesn't seem to work. First, here's a working example with a public and known identifier:

struct ReleaseView: View {
    let id: Int

    var body: some View {
        GeometryReader { _ in
            VStack(spacing: 16) {
                Image(nsImage: NSImage(named: NSImage.networkName)!)
                    .contentShape(Rectangle())
                    .onDrag {
                        return NSItemProvider(item: "\(self.id)" as NSString, typeIdentifier: NSPasteboard.PasteboardType.string.rawValue)
                    }

                DropZone()
            }
        }
    }
}

struct DropZone: View {
    @State var isDragging = false

    var body: some View {
        RoundedRectangle(cornerRadius: 16)
            .stroke(style: StrokeStyle(lineWidth: 4, dash: [8, 8]))
            .background(isDragging ? Color.secondary : Color.clear)
            .frame(width: 100, height: 100)
            .onDrop(of: [NSPasteboard.PasteboardType.string.rawValue], isTargeted: self.$isDragging) { itemProvider in
                print(itemProvider)
                return true
            }
    }
}

In this example, you can drag the image above into the drop zone and it will print out the provider. Now, merely changing the typeIdentifier breaks everything.

static let sharedTypeIdentifier = "com.procrastin8.plzwork"

struct ReleaseView: View {
    // skipping the unchanged bits

                    .onDrag {
                        return NSItemProvider(item: "\(self.id)" as NSString, typeIdentifier: sharedTypeIdentifier)
                    }
}

struct DropZone: View {
    // skipping the unchanged bits

           .onDrop(of: [sharedTypeIdentifier], isTargeted: self.$isDragging) { itemProvider in
                print(itemProvider)
                return true
            }
}

Now this doesn't work. Using the same constant here, so it's not a string mismatch. Just yet another SwiftUI bug?

Answer 1

The typeIdentifier in above is not just a unique string, it must be UTI.

If you want to use some custom-application-specifc UTI (think twice if you really need it), then you have to register one according to Apple rules, starting from

<key>UTExportedTypeDeclarations</key>
        <array>
            <dict>
                <key>UTTypeIdentifier</key>
                <string>com.procrastin8.plzwork</string>
                ...

in app Info.plist

See details specifically in Declaring New Uniform Type Identifiers

And wide collection in Technical Q&A QA1796

Answer 2

Nowadays, you can add a type identifier through target project and it adds the UTI string automatically on the Info.plist, as explained on this Raywenderlich article.

---

Walkthrough

1. Select the project on Project Navigator
2. Select the project target under "Targets" section
3. Select the "Info" tab
4. Expand "Exported Type Identifiers"
5. Click + to add a new UTI
6. Enter a description for the Description field
7. Enter your identifier for the Identifier field with the same value you used in your code
8. Under Conforms To enter public.data