NSCollectionView Drag and Drop

Issue with NSCollectionView's default drag and drop implementation

Sample project

This is a sample project to demonstrate an issue I'm having when using the Drag and Drop behaviour for multiple items in NSCollectionView.

Issue

I want to recreate the Drag and Drop behaviour of the macOS Photos.app: when selecting multiple items to reorganise them, the items are animated quickly into a pile formation (a seemingly randomly assorted pile of images).

The default implementation of NSDraggingDestination provided by NSCollectionView seems to have a few issues:

• slow to animate the flock of images when dragging multiple items and moving the cursor, and the red badge indicating the number of items is awkwardly close to the cursor (see gif below)
• setting the NSDraggingInfo's or NSDraggingSession's draggingFormation property doesn't seem to have any effect, anywhere I set it

Possible solutions

NOT making the NSCollectionView a Drop destination

By not implementing:

• collectionView(_:writeItemsAt:to:) nor
• collectionView(_:pasteboardWriterForItemAt:) seems to fix both issues (probably because the destination defaults to a superview, which relies on a NSView's default implementation of NSDraggingDestination). But it introduces a new obvious issue: The CollectionView is not a drop destination anymore...

Opting out of NSDraggingDestination's default implementation

Opting out of NSDraggingDestination's default implementation provided by NSCollectionView by simply overriding draggingEntered(_:) and not calling super's implementation:

class CustomCollectionView: NSCollectionView {

    override func draggingEntered(_ sender: NSDraggingInfo) -> NSDragOperation {
        return .move
    }

}

seems to fix the draggingFormation's issue, but again, a lot of work needs to be re-done to re-implement all of the "Drop destination" behaviour that come for free with NSCollectionView.

Help

If you feel you can help, please open an issue, or a PR, send me an email at github@jeanetienne.net or contribute to the StackOverflow question Thanks!