Instance Method


Notifies your delegate that a drag session is about to begin.


optional func collectionView(_ collectionView: NSCollectionView, draggingSession session: NSDraggingSession, willBeginAt screenPoint: NSPoint, forItemsAt indexes: IndexSet)



The collection view notifying your delegate object.


The dragging session that is about to begin.


The starting point (in screen coordinates) for the drag operation.


The indexes of the items being dragged.


You can use this method to modify the dragging session or to perform other tasks related to the beginning of a drag session.

See Also

Legacy Collection View Support

func collectionView(NSCollectionView, canDragItemsAt: IndexSet, with: NSEvent) -> Bool

Returns a Boolean indicating whether the collection view can begin dragging the specified items.

func collectionView(NSCollectionView, pasteboardWriterForItemAt: Int) -> NSPasteboardWriting?

Provides the pasteboard writer for the item at the specified index

func collectionView(NSCollectionView, writeItemsAt: IndexSet, to: NSPasteboard) -> Bool

Invoked after it has been determined that a drag should begin, but before the drag has been started.

func collectionView(NSCollectionView, namesOfPromisedFilesDroppedAtDestination: URL, forDraggedItemsAt: IndexSet) -> [String]

Invoked to return an array of filenames that the receiver promises to create.

func collectionView(NSCollectionView, acceptDrop: NSDraggingInfo, index: Int, dropOperation: NSCollectionView.DropOperation) -> Bool

Invoked when the mouse is released over a collection view that previously allowed a drop.