How do you detect when a file is changed in iCloud

问题:

When a file is changed in iCloud (whether added, deleted, or the content changed), I would like to call a method I created ([self methodName]) so that I can update my table view with the names of the new files. How am I notified of the file change? Do I need to listen for a NSNotification (if so, what is it?) or do I have to check manually? Thanks.

回答1:

The name of the NSNotification I have to listen for is NSMetadataQueryDidUpdateNotification. This is how I did it:

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(queryDidUpdate:) name:NSMetadataQueryDidUpdateNotification object:query];

...

-(void)queryDidUpdate:(NSNotification *)notification {

    //something changed, reload (NSMetadataQuery, create NSPredicate, rerun the query, etc.)

}

回答2:

This section of the Apple developer website contains a great tutorial for setting up document-based iCloud apps.

To answer your questions, though: as long as your document is a UIDocument you can register for a notification. Just search that page for "Monitoring Document-State Changes and Handling Errors" - there is tons of source code to help you out.