iCloud - renaming open documents on another device sometimes fails

Question

The issue: I'm working on an iCloud document on device A, e.g. iPod Touch. Then I change the name of the document on device B, e.g. my Mac (via the Finder). The change goes up to the cloud and after a pause device A gets to hear about it.

And then:

• some of the time all is just fine - I pick up the change of name via a changed fileURL property and can update my interface accordingly - the document continues to behave just as it should
• some of the time, the document's fileURL is returned as something such as: file://localhost/var/mobile/Library/Mobile%20Documents/.ubd/peer-43A0AEB6-84CE-283E-CA39-FCC4EF3BC8F8-v23/ftr/purg-012fdcfbe3b3bbce6e603fdfd2f000b2cb28649e95 Not surprisingly this file won't save.

Can anyone explain what is going on and how to work around it?

Background

• The name change is picked up fine by by NSMetadataQuery. So, for e.g., I can rename documents that are not open and all my iCloud functionality works fine. The issue only seems to occur with open documents.

• Other iCloud features are working fine, e.g. I can change content on one device, e.g. my Mac, and detect and then update my interface on another device, e.g. my iPod Touch, that has the relevant iCloud document open.

• I first spotted this when I added an override for presentedItemDidMoveToURL: to my UIDocument subclass. The override reliably picks up name changes made in the cloud, e.g. renaming the document on another device. Then sometimes newURL is the final expected URL for the renamed document, i.e. something sensible from which I can extract the new name use `lastPathComponent', update my interface etc. On other occasions newURL is a document in some other directory with a last path component beginning 'purg-', e.g. purg-012fdcfbe3b3bbce6e603fdfd2f000b2cb28649e95.

  - (void) presentedItemDidMoveToURL:(NSURL *) newURL;
  {   
      [super presentedItemDidMoveToURL: newURL];
  
      if ([(id)[self delegate] respondsToSelector:@selector(documentNameChanged:)])
      {
          [[self delegate] documentNameChanged: self];
      }
  }
  

• The presentedItemDidMoveToURL: method does not seem to be the root cause of the problem. For example, if I don't override that method at all, but periodically check in the viewController that is looking after the open document, then sometimes after a rename fileURL will return the new name and sometimes it will return `purg-.....'. So the issue appears to be to do with how renaming is handled.

Update

As al_lea pointed out, the issue here was related to accommodatePresentedItemDeletionWithCompletionHandler:. Expanding on al_lea's answer, I added the code below to my UIDocument subclass. This fixed the issue.

    - (void) accommodatePresentedItemDeletionWithCompletionHandler: (void (^) (NSError *errorOrNil)) completionHandler
    {    
        PresentedDocument* presentedDocument = [self retain];
        [presentedDocument closeWithCompletionHandler: ^(BOOL success) {        
            NSError* error = nil;
            if (!success)
            {
                NSDictionary* userInfo = [NSDictionary dictionaryWithObjectsAndKeys:
                    @"Could not close document that is being deleted on another device",
                    NSLocalizedDescriptionKey, nil];
                    error = [NSError errorWithDomain: @"some_suitable_domain"
                                                code: 101
                                           userInfo: userInfo];
            }

        completionHandler(error);  // run the passed in completion handler (required)

        dispatch_async(dispatch_get_main_queue(), ^
        {
           [[NSNotificationCenter defaultCenter] postNotificationName: NOTIFY_presentedDocumentDeletedOnAnotherDevice
                                                               object: presentedDocument
                                                             userInfo: nil];

           [presentedDocument tidyUpAfterDelete];  // app specific tidy up
           [presentedDocument release];
       });
    }];
}

With this code in place, there are no spurious and confusing presentedItemDidMoveToURL: calls made and, in addition, the relevant object can listen for notifications of deletions on other devices.

Answer 1

This type of URL appears when a UIDocument is opened on local and get deleted from a remote device:

file://localhost/var/mobile/Library/Mobile%20Documents/.ubd/peer-43A0AEB6-84CE-283E-CA39-FCC4EF3BC8F8-v23/ftr/purg-

You need to close the document first before it get deleted - detect this in NSFilePresenter's accommodatePresentedItemDeletionWithCompletionHandler: