How to Allow Users To Drag Files Out of Cocoa App

Question

I am working on a macOS application that involves creating a folder in a temporary directory.

How can I allow users to drag a folder icon off of the Cocoa app and onto their desktop (or into Finder and other apps) so that dropping it will actually paste the folder created by the app?

I have so far been able to write the finished folder that I want to save to a temporary directory. How do I place a folder icon on the application that can be dragged into the Finder? Thanks!

The complete code I'm currently using is this:

    class draggableFolder: NSImageView {
    override func mouseDown(with theEvent: NSEvent) {
        let pasteboardItem = NSPasteboardItem()
       // pasteboardItem.availableType(from: [NSPasteboard.PasteboardType.fileURL])
        pasteboardItem.setDataProvider(self, forTypes: [kUTTypeURL as NSPasteboard.PasteboardType])
        let draggingItem = NSDraggingItem(pasteboardWriter: pasteboardItem)
        draggingItem.setDraggingFrame(self.bounds, contents:self.image)

        beginDraggingSession(with: [draggingItem], event: theEvent, source: self as NSDraggingSource)
    }


}

extension draggableFolder: NSDraggingSource {
    func draggingSession(_ session: NSDraggingSession, sourceOperationMaskFor context: NSDraggingContext) -> NSDragOperation {
        return NSDragOperation.generic
    }
}

extension draggableFolder: NSPasteboardItemDataProvider {
    func pasteboard(_ pasteboard: NSPasteboard?, item: NSPasteboardItem, provideDataForType type:
        NSPasteboard.PasteboardType) {
        print("dataprovider")
        if let pasteboard = pasteboard, type.rawValue == String(describing: kUTTypeURL) {
           let folder = currentIconsetURL
            print("dataprovider2")
            print(NSURL.init(fileURLWithPath: currentIconsetURL))
            pasteboard.clearContents()
            pasteboard.declareTypes([NSPasteboard.PasteboardType.fileNameType(forPathExtension: "appiconset")], owner: nil)
            pasteboard.writeObjects([(URL.init(fileURLWithPath: currentIconsetURL).absoluteURL as NSURL) as NSPasteboardWriting])


        }
    }
}

Answer 1

Sadly, the drag and drop guide Apple has is based entirely on the old deprecated API: https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/DragandDrop/DragandDrop.html

The rough outline for what you're asking, using the modern API is:

• You need something (ex, your view) to implement the NSDraggingSource protocol to return that it supports the Copy operation only (draggingSession(_:sourceOperationMaskFor:)).
• From within mouseDown (with a tracking loop) or mouseDragged, once the user's drag has moved a certain distance from its original location (3 or 4 points is all), then you should start a dragging session (NSView beginDraggingSession)
• The session should contain one NSDraggingItem where you pass in the URL for the folder (as an NSURL, not a Swift URL, because only the former conforms to NSPasteboardWriter).