NSpasteboard writeObjects bug in Mojave

Did you come up with a workaround or anything? I'm hitting this also.

So, what is the answer to the question ?

looking for an answer to this error

Yeah, seeing "Correct answer" led me believing I would find the solution here… Nope.

I got a variation of the error originally reported above: "There are 0 items on the pasteboard, but 1 drag images. There must be 1 draggingItem per pasteboardItem."

I was able to get rid of that error by setting an empty string in pasteboardWriterForItem (to make it look like there was 1 draggingItem after this call):

func outlineView(_ outlineView: NSOutlineView,
                     pasteboardWriterForItem item: Any) -> NSPasteboardWriting? {

        let pasteboardItem = NSPasteboardItem()
       
        pasteboardItem.setString("", forType: NSPasteboard.PasteboardType.string)
       
        return pasteboardItem
}

Previously, I just returned an initialized NSPasteboardItem only (e.g. I added line 6).

Hopefully this, or a variation of it, will work for you.

Actually if you are using the pasteboardWriterFor.. delegates it will work fine. Unfortunately, NSBrowser has so such API (yet?) so I'm stuck.

I have filed a bugreport and it's being invetigated.

I suspect there is more than one possible cause of this error, but here's the solution I found for my own app in case it helps anyone. I determined the error was caused by using two different methods of writing data to the pasteboard. My old code looked something like this:

- (BOOL)tableView:(NSTableView *)tableView writeRowsWithIndexes:(NSIndexSet *)rowIndexes toPasteboard:(NSPasteboard *)pboard {
NSUInteger count = rowIndexes.count;
[pboard declareTypes:@[JUNUTTypeRowIndexes,NSFilesPromisePboardType] owner:self];
NSMutableData *data = …
[pboard setData:data forType:JUNUTTypeRowIndexes];
NSMutableArray *extensions = …
[pboard setPropertyList:extensions forType:NSFilesPromisePboardType];
NSArray *urls = …
[pboard writeObjects:urls];
return YES;
}

Note that URLs are not included in declareTypes: because I was using the new writeObjects: API for those. This works fine in older versions of macOS but causes this error in Mojave. I wanted to find the simplest solution possible for a quick bug fix release, and found that using the same API for all my data types fixes the problem:

- (BOOL)tableView:(NSTableView *)tableView writeRowsWithIndexes:(NSIndexSet *)rowIndexes toPasteboard:(NSPasteboard *)pboard {
  NSUInteger count = rowIndexes.count;
  [pboard declareTypes:@[JUNUTTypeRowIndexes,NSFilesPromisePboardType,NSURLPboardType] owner:self];
  NSMutableData *data = …
  [pboard setData:data forType:JUNUTTypeRowIndexes];
  NSMutableArray *extensions = …
  [pboard setPropertyList:extensions forType:NSFilesPromisePboardType];
  NSURL *url = …
  [url writeToPasteboard:pboard];
  return YES;
}

With this change, NSURLPboardType is now included in declareTypes: and NSURL's writeToPasteboard: method is used to write the URL to the pasteboard.

If you don't mind doing a more significant rewrite, the more modern way to handle all of this is with tableView:pasteboardWriterForRow:. This method lets you return an object that conforms to NSPasteboardWriting. That object should use writableTypesForPasteboard: to declare the content types it supports, and pasteboardPropertyListForType: to return the actual data for the requested type.

I've added

[pasteboard clearContents];

before

[pasteboard writeObjects:objects];

and currently it helped.

Is there any update on this?