Cannot get drag and drop to work onto NSCollectionView - objective-c

Question

There is probably a simple mistake that I'm making, but I simply cannot get dropping of files onto an NSCollectionView to work even in the most basic way.
In a test project, I have an NSCollectionView on a window, and the view controller is both its delegate and data source. I want to be able to drag files from the Finder onto this collection view.
From reading the docs, all I should have to do is:
Register for dragged type(s):
- (void)viewDidLoad {
[super viewDidLoad];
// Do any additional setup after loading the view.
NSLog(#"Registering dragged types for collection view: %#", self.collectionView);
[self.collectionView registerForDraggedTypes:#[NSFilenamesPboardType]];
[self.collectionView setDraggingSourceOperationMask:NSDragOperationEvery forLocal:YES];
[self.collectionView setDraggingSourceOperationMask:NSDragOperationEvery forLocal:NO];
}
And then implement these two methods:
-(NSDragOperation)collectionView:(NSCollectionView *)collectionView validateDrop:(id<NSDraggingInfo>)draggingInfo proposedIndex:(NSInteger *)proposedDropIndex dropOperation:(NSCollectionViewDropOperation *)proposedDropOperation {
NSLog(#"Validate drop: %#", draggingInfo);
return NSDragOperationMove;
}
-(BOOL)collectionView:(NSCollectionView *)collectionView acceptDrop:(id<NSDraggingInfo>)draggingInfo index:(NSInteger)index dropOperation:(NSCollectionViewDropOperation)dropOperation {
NSLog(#"Accept drop: %#", draggingInfo);
return YES;
}
But none of the two methods is ever called, when I try to drag an item onto the collection view, which makes me think that the registerForDraggedTypes: call is not working as expected.
What can be the issue here? What else do I have to look into?

Answer 1

From OS X 10.11 the NSCollectionViewDelegate methods take an index path instead of an index. For instance in
-(NSDragOperation)collectionView:(NSCollectionView *)collectionView validateDrop:(id<NSDraggingInfo>)draggingInfo proposedIndex:(NSInteger *)proposedDropIndex dropOperation:(NSCollectionViewDropOperation *)proposedDropOperation
the proposedIndex: parameter is replaced by proposedIndexPath:
- (NSDragOperation)collectionView:(NSCollectionView *)collectionView validateDrop:(id <NSDraggingInfo>)draggingInfo proposedIndexPath:(NSIndexPath * __nonnull * __nonnull)proposedDropIndexPath dropOperation:(NSCollectionViewDropOperation *)proposedDropOperation