I am seriously pulling out my hairs on this one… I have an NSOutlineView where I want local drag’n’drop, and I have these methods in my datasource:

• (NSDragOperation)outlineView:(NSOutlineView*)outlineView validateDrop:(id )info proposedItem:(id)item proposedChildIndex:(int)index { return NSDragOperationMove; }

• (BOOL)outlineView:(NSOutlineView)outlineView writeItems:(NSArray)items toPasteboard:(NSPasteboard*)pboard { [pboard declareTypes:[NSArray arrayWithObjects:@”MyItemsPboardType”, nil] owner:nil]; [pboard setPropertyList:items copy] autorelease] forType:@”[[MyItemsPboardType”]; return YES; }

• (BOOL)outlineView:(NSOutlineView*)outlineView acceptDrop:(id )info item:(id)anItem childIndex:(int)index { NSPasteboard* pboard = [info draggingPasteboard];

  NSString* type = [pboard availableTypeFromArray:[NSArray arrayWithObjects:@”MyItemsPboardType”, nil]]; NSArray* items = [pboard propertyListForType:type];

  NSLog(@”Available type: %@”, type); NSLog(@”Drag items: %@”, items); }

It does report the MyItemsPboardType when I drag and drop items, but the array is nil. Did I overlook something?

For the records, I also added this to my NSOutlineView subclass:

• (NSDragOperation)draggingSourceOperationMaskForLocal:(BOOL)isLocal { return isLocal ? NSDragOperationMove : NSDragOperationCopy; }

Ahh, figured it out! The setPropertyList: takes a property list, which is an array containing property list items, i.e. not my own items, these are stripped… frustrating…

Is there any easy way to store custom items on the pasteboard? It would seem I am forced to serialise my items into an NSData or similar…

And after fiddling with NSArchiver, I realise this is not what i want – I want the pointers to stay the same, serialising and unserialising results in a copy of the original items, I need the original items so that they can be removed from the outline view… arg… I see that the DragNDrop example just uses a instance variable to store the items during the drag… so much for the drag pasteboard to carry the data for local drags…

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You shouldn’t really drag pointers to your items during a drag. Dragged items can be dropped in other applications, or can be dropped on the desktop, where they’ll be saved as a clipping file. If you put a pointer in your drag, someone may create a clipping file, quit your application (releasing the pointer implicitly), restart your application and drop the now stale pointer back into your app. bang

That said, you could just cast your pointer to a long and store it in an NSNumber, and attach that to your drag as a property list. You might want to put it into a dictionary, with a second entry that contains a timestamp that indicates when the drag started, and an NSData representation of your object. When you get a drop, check the timestamp against that of the most recent drag. If they don’t match, it’s likely a clipping file, so just create a new item from the NSData. Otherwise you can use the pointer.

NB - Just saw you’re doing a local drag. I guess in that case it’s fine to just stuff your pointer in an NSNumber. – UliKusterer