Drag & Drop between Photos and a Sandboxed app - cocoa

Question

I have a Sandboxed app. I'd like the user to be able to drag a picture from the Photos app into my sandboxed app.
I wrote all the code for handling the "promised file" from Photos no problem when using it with a not sandboxed app. But with my sandboxed app, Photos is telling me it has no right to write the picture file in the destination folder... which is the temporary folder inside my sandboxed app.
That's kind of logical that Photos can't write inside my sandbox, even in the temporary folder. But as my app has no access outside the sandbox, how can I exchange the file from Photos to my App ???
Edit to provide some code as per request
NSString *tempPath = [NSTemporaryDirectory() stringByAppendingPathComponent:[[NSUUID UUID] UUIDString]] ;
NSError *error = nil ;
[[NSFileManager defaultManager] createDirectoryAtPath:tempPath
withIntermediateDirectories:NO
attributes:nil
error:&error] ;
filenames = [sender namesOfPromisedFilesDroppedAtDestination:[NSURL fileURLWithPath:tempPath]] ;
(filenames is global variable NSArray)
And the error message that Photos is showing (SOrry, the picture is in French, but the message isn't really usefull as it can't be shown completely. The part that is shown says "0 file (out of 1) exported. Impossible to move "image" to "folder" : either this folder does not exist, or the folder can't be //cut//
I of course checked that the folder does exist.
Edit with some more information
I think I found one investigation path :
When I create the unique folder in the temporary folder, it gets a "quarantine" flag. I checked that using the terminal and "ls -l", one can see a "#" after the permissions. Now, If I don't create the unique folder, Photos can drop the file directly in the temporary folder. Therefore the problem is that Photos can't use the "quarantined" folder.
Now this does not help yet. As anyway the drop picture file also has the quarantine flag set, my App can't read it !
I have found no way to get rid of those quarantine flags.
The strangest thing is that everything is working fine if I just step by step with the debugger.

Answer 1

The Sandbox will allow file promise provider application to write into the Document folder.
[[NSFileManager defaultManager] URLForDirectory:NSDocumentDirectory inDomain:NSUserDomainMask appropriateForURL:nil create:YES error:NULL];

Answer 2

OK, I found what was wrong. It has nothing to do with quarantine or app being sand-boxed.
In fact, when namesOfPromisedFilesDroppedAtDestination: is called, the provider application (in my case Photos) starts writing the files in the temporary folder. This can take some time. Therefore, I was starting to monitor the events in the destination folder, and was reacting on the first event only. (check this : How can my OS X app accept drag-and-drop of picture files from Photos.app?).
BUT
The Photos app is sending the files in several steps. The first steps create a temporary file, which is later renamed to the "correct" image file. This creation of temporary file was the event that my app captured. My app was then checking for the image file to be present, and it wasn't, yet.
The solution is therefore, to continue checking for folder events until the promised file is really there. If it is not yet, then continue waiting. Hopefully, the promising app will fulfill its promise one day.
Thanks to catlan for pushing me to re-investigate.