objective c - NSMetaDataQuery never calls back with NSMetadataQueryDidFinishGatheringNotification

Question

For an iCloud plugin I'm writing, I subscribe my iCloud manager class to these iCloud NSMetaDataQuery observers:

// Add a predicate for finding the documents
NSString* filePattern = [NSString stringWithFormat:@"*.%@", @"*"];

self.metadataQuery = [[NSMetadataQuery alloc] init];

// Before starting to query, it is required to set the search scope.
arrayWithObject:NSMetadataQueryUbiquitousDocumentsScope]];

// It is also required to set a search predicate.
[self.metadataQuery setPredicate:[NSPredicate predicateWithFormat:@"%K LIKE %@", NSMetadataItemFSNameKey, filePattern]];

// Listen for the second phase live-updating
[[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(queryDidReceiveNotification:) name:NSMetadataQueryDidUpdateNotification object:nil];

// Listen for the first phase gathering
[[NSNotificationCenter defaultCenter] addObserver:self
                                      selector:@selector(queryIsDoneGathering:) name:NSMetadataQueryDidFinishGatheringNotification
                                           object:nil];

[self.metadataQuery startQuery];

The problem is that none of these selectors are actually ever called back, not even once, and I especially need the NSMetaDataQueryDidUpdateNotification to track upload/download progress of files in the cloud.

An odd thing is that I had this working the other day, but somehow it just stopped working and I've starred myself blind in trying to figure out what the problem actually is. By subscriping to the NSMetadataQueryDidStartGatheringNotification I can see that it does start, but it's like it never finishes. It is quite weird.

I was wondering if anyone have any clue at all as what to be wrong with the above code? Or where else I can look for the problem.

Thank you for your time :)

Answer 1

Make sure you start the NSMetadataQuery in the main thread. Back then this requirement was not documented.