Drag & Drop issues in SwiftUI in a Playground App

I am prototyping an iOS App in Swift Playgrounds. The App has Drag & Drop features internally using custom identifiers.

The data that is being moved around is a struct that contains a deeplink URL that can be used to identify my models.

I have three different entities to deal with. One is identified with a UTI com.example.item, the other two as com.example.collection. Items may be dropped onto Collections and visa versa, but the same type my not be dropped onto itself.

For onDrag(_:) I produce an NSItemProvider and register the entity using registerDataRepresentation(forTypeIdentifier: visibility: loadHandler:). The ‘loadHandler’ encodes the URL of the entity as Data. I use the appropriate custom UTI String for the entity.

So far so good, I can see that the right UTI String has been registered by examining the NSItemProvider.

For onDrop(of:delegate:) I provide the valid UTI (this filter does not seem to be honoured) and a custom class implementing DropDelegate, giving it a reference to the entity at the drop target.

As the filter does not seem to work, my DropDelegate implements func validateDrop(info: DropInfo) -> Bool.

In this function, I attempt to filter which drops are valid by calling info.hasItemConformingTo(_:) and checking against the drop target.

What I am finding is that even though I can see my custom UTI strings have been registered in the NSItemProviders, they are never visible when calling hasItemConformingTo(_:).

In this situation I would be unable to implement performDrop AFAICS.

I wonder if this problem is to do with my misunderstanding of how Drag & Drop works (I have also attempted other approaches like registering custom Objects with the NSItemProvider, but have the same problem.

Is this possibly caused by my environment? As I am writing this prototype in Swift Playgrounds, where there is no Info.plist, so I am unable to register custom UTI schemes?

Many thanks for any suggestions.