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.

It might be worth noting that there is a mention of this exception in the 10.14 Release Notes:

https://developer.apple.com/documentation/macos_release_notes/macos_mojave_10_14_release_notes/appkit_release_notes_for_macos_10_14?language=objc

(Look for "Drag & Drop").

However, I find what is written there quite confusing:

I am using tableView:writeRowsWithIndexes:toPasteboard, which causes this exception when dragging multiple items. THe 10.14 Release Notes make it sound like this API is deprecated. I cannot find any mention if it being deprecated though, neither in the documentation nor the header.

As according to the release notes I should be using tableView:pasteboardWriterForRow: instead, I have done this and it fixes the exception.

But - I also need to override the drag image of a multi item drag with a SINGLE image (like seen in Mail.app), and was using

dragImageForRowsWithIndexes:tableColumns:event:offset:, which is no longer called when using pasteBoardWriter. So this unforunately is no solution for me.

None of this change in behaviour (like when dragImageForRowsWithIndexes:tableColumns:event:offset: is called or not called) seems to be documented anywhere, which makes this all quite a frustrating trial and error experience.

If anybody could provide more insight into what is or is not actually deprecated, a bug or a misunderstanding of the API, this would be very helpful.

Cheers

Thomas

Is there any update on this?

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 filed FB5417493 way back in 2019. This NSBrowser bug still exists on macOS Tahoe 26.2 (so nearly 7 years later, happy new year).

I've been avoiding the issue all this time by using the deprecated API:

-(BOOL)browser:(NSBrowser*)browser
writeRowsWithIndexes:(NSIndexSet*)rowIndexes
      inColumn:(NSInteger)column
  toPasteboard:(NSPasteboard*)pasteboard
{
// Code here....
NSArray <NSURL*>*urls = // get urls for columns/rows..
BOOL didWrite = NO;
   if (@available(macOS 10.14,*))
    {
         NSArray *filenames = [self fileNamesFrommURLs:urls];
// ironically need to use deprecated API on newer OS's
    [pasteboard declareTypes:@[NSFilenamesPboardType] owner:self];
        didWrite = [pasteboard setPropertyList:filenames forType:NSFilenamesPboardType];
}
else
{
// I can just write urls
 didWrite = [pasteboard writeObjects:urls];
}
return didWrite;
}

But I raised the deployment target so now I'm getting warning which I guess I have to suppress. There is no way to provide more than one drag image with NSBrowser without using private API because the delegate method only accepts one image:

-(NSImage*)browser:(NSBrowser*)browser draggingImageForRowsWithIndexes:(NSIndexSet*)rowIndexes inColumn:(NSInteger)column withEvent:(NSEvent*)event offset:(NSPointPointer)dragImageOffset

I'm not sure why there is an "Accepted Answer" on this thread because the accepted answer doesn't answer anything and only asks more questions.