# collectionView(_:validateDrop:proposedIndex:dropOperation:) Validates the specified location to see if it is a valid drop target. ``` @MainActor optional func collectionView(_ collectionView: NSCollectionView, validateDrop draggingInfo: any NSDraggingInfo, proposedIndex proposedDropIndex: UnsafeMutablePointer, dropOperation proposedDropOperation: UnsafeMutablePointer) -> NSDragOperation ``` ## Parameters `collectionView` The collection view that send the message. `draggingInfo` An object containing details about this dragging operation. `proposedDropIndex` The proposed drop index. This parameter is passed by-reference and can be modified retarget the drop operation. `proposedDropOperation` The proposed drop operation. This parameter is passed by-reference and can be modified to change the drop operation. ## Return Value A value that indicates which dragging operation to perform. Return [`NSDragOperationNone`](/documentation/AppKit/NSDragOperation/NSDragOperationNone) to disallow the drop. ## Discussion Based on the mouse position, the collection view will suggest a proposed index and drop operation. These values are in/out parameters and can be changed by the delegate to retarget the drop operation. The collection view will propose `NSCollectionViewDropOn` when the dragging location is closer to the middle of the item than either of its edges. Otherwise, it will propose `NSCollectionViewDropBefore`. You may override this default behavior by changing `proposedDropOperation` or `proposedDropIndex`. To receive drag messages, you must first send [`registerForDraggedTypes(_:)`](/documentation/AppKit/NSView/registerForDraggedTypes(_:)) to the collection view with the drag types you want to support. You must implement this method for your collection view to be a drag destination. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)