filePromiseProvider writePromiseTo URL not working when dragging image to another application

Question

I have File Promises implemented in a Cocoa app that allows dragging images from a view and dropping them to folders on the machine or to apps like preview or evernote. In the past this has worked well using the NSDraggingSource delegate and 'namesOfPromisedFilesDropped' method. This method would return the drop location and would allow me to write the image data directly there. So when dropping to an application icon like preview, or within an app like evernote, the file would be written and the app would either load or the image would simply show within.

Unfortunately this method was deprecated in 10.13 so it no longer gets called in new OS versions. Instead I've switched over to using the filePromiseProvider writePromiseTo url method of the "NSFilePromiseProviderDelegate" delegate. This method gets called, and the image data is processed. I get the destination URL and attempt to write the image data to this location. This works perfectly fine when simply dragging to folders on the Mac. But, when dragging to other app icons like Preview.app, or directly to a folder in Evernote, I get an error 'Error Domain=NSPOSIXErrorDomain Code=2 "No such file or directory"'.

I've attempted this using full URLs, and, URL paths. Regardless of either, when dragging to other apps it simply will not allow the drop or creation of the file at that location.

Is there some entitlement that may be missing? I've even attempted the Apple source code found here with the same error: File Promises Source

Here is the code I'm using now that's returning the error with inability to write to outside app locations. This only works for dragging to folders on the computer.

extension DragDropContainerView: NSFilePromiseProviderDelegate {
    internal func filePromiseProvider(_ filePromiseProvider: NSFilePromiseProvider, fileNameForType fileType: String) -> String {
        let fileName = NameFormatter.getFormattedNameFromDate() + "." + fileType.getFileType().typeIdentifier
        return fileName
    }

    internal func operationQueue(for filePromiseProvider: NSFilePromiseProvider) -> OperationQueue {
        return workQueue
    }

    internal func filePromiseProvider(_ filePromiseProvider: NSFilePromiseProvider, writePromiseTo url: URL, completionHandler: @escaping (Error?) -> Void) {
        if let snapshot = filePromiseProvider.userInfo as? SnapshotItem {
            if let data = snapshot.representationData {
                do {
                    try data.write(to: url)
                    completionHandler(nil)
                } catch {
                    completionHandler(error)
                }
            }
        }
    }
}

Any help on this issue would be great. Ultimately, I simply want to be able to drag the image to an app and have that app accept the drag. This used to work but no longer does.

Update 1: After extensive experimentation I've managed to find a 'solution' that works. I don't see why this works but some how this ultimately kicks off a flow that fires the old 'deprecated' method.

I create the dragged item;

let draggingItem = NSDraggingItem(pasteboardWriter: pasteboardWriter(forImageCanvas: self))
                    draggingItem.setDraggingFrame(screenshotImageView.frame, contents: draggingImage)
                    beginDraggingSession(with: [draggingItem], event: event, source: self)

This calls the below method;

private func pasteboardWriter(forImageCanvas imageCanvas: DragDropContainerView) -> NSPasteboardWriting {
    let provider = FilePromiseProvider(fileType: kUTTypeJPEG as String, delegate: self)
    provider.userInfo = imageCanvas.snapshotItem
    return provider
}

This sets up the custom file promise session using the subclass below. As you can see, I'm not handling any logic here and it seems to be doing very little or nothing. As an added test to verify it's not really doing much, I'm setting the pasteboard type to 'audio'. I'm dragging an image not audio but it still works.

public class FilePromiseProvider : NSFilePromiseProvider {
   public override func writableTypes(for pasteboard: NSPasteboard)
    -> [NSPasteboard.PasteboardType] {

        return [kUTTypeAudio as NSPasteboard.PasteboardType]
   }

   public override func writingOptions(forType type: NSPasteboard.PasteboardType,
                                    pasteboard: NSPasteboard)
    -> NSPasteboard.WritingOptions {
        return super.writingOptions(forType: type, pasteboard: pasteboard)
   }
}

So long at the above methods are implemented it apparently kicks off a flow that ultimately calls the 'deprecated' method below. This method works every time perfectly in Mojave showing that there must be an issue with the NSFilePromises API. If this method works, the file promises API should work the same but it does not;

override func namesOfPromisedFilesDropped(atDestination dropDestination: URL) -> [String]?

Once this method gets called everything works perfectly in Mojave for drags to app icons in the dock and directly into applications like Evernote returning the app to 100% drag drop functionality as it used to work in previous OS versions!

My file promises delegate is still in place but looks like the below. As you can see it's not doing anything any longer. However it's still required.

extension DragDropContainerView: NSFilePromiseProviderDelegate {
   func filePromiseProvider(_ filePromiseProvider: NSFilePromiseProvider, fileNameForType fileType: String) -> String {
       return ""
   }

   func filePromiseProvider(_ filePromiseProvider: NSFilePromiseProvider, writePromiseTo url: URL, completionHandler: @escaping (Error?) -> Void) {

   }
}

Any comments on this 'solution' would be great. Any suggestions on how to do this better would also be welcomed. Please note, that according to Apple, there "is no guarantee that the file will be written in time" using the File Promises API. But with the above, the old deprecated method is somehow called in Mojave and works flawlessly every time.

Thanks