如何强制iCloud与核心数据进行同步？

Question

I'm using iCloud with core data to sync data of my App.

I tried everything and finally It works perfectly.

but I have one question.

Is there any way that saying to iCloud to sync?

It sync when app begin, but the other time. It seems like that it sync randomly. I can't find the way to handle it myself.

any help?

Thanks.

Answer 1

I figured out how to force a core data store to sync to iCloud. You just need to "touch" any receipt files in the Data folder in the Ubiquity filesystem. The code below will do this. To force a sync, call the syncCloud method. For every "receipt" file it finds, it will update the files modification time stamp to the current time, essentially doing a "touch" on the file. As soon as this happens, iCloud will check and sync any core data files that need synchronization in iCloud. Near as I can tell, this is how the simulator or Xcode does it when you select the "Trigger iCloud Sync" option.

@property (strong, nonatomic) NSMetadataQuery  *query;

-(void) init
{
    self.query = [[NSMetadataQuery alloc] init];

    [[NSNotificationCenter defaultCenter] addObserver: self
                                             selector: @selector(didFinishMetadataQuery)
                                                 name: NSMetadataQueryDidFinishGatheringNotification
                                               object: self.query];
}

-(void) didFinishMetadataQuery
{
    // Query completed so mark it as completed
    [self.query stopQuery];

    // For each receipt, set the modification date to now to force an iCloud sync
    for(NSMetadataItem *item in self.query.results)
    {
        [[NSFileManager defaultManager] setAttributes: @{NSFileModificationDate:[NSDate date]}
                                         ofItemAtPath: [[item valueForAttribute: NSMetadataItemURLKey] path]
                                                error: nil];
    }
}

-(void) syncCloud
{
    // Look for files in the ubiquity container data folders
    [self.query setSearchScopes:@[NSMetadataQueryUbiquitousDataScope]];

    // Look for any files named "receipt*"
    [self.query setPredicate:[NSPredicate predicateWithFormat:@"%K like 'receipt*'", NSMetadataItemFSNameKey]];

    // Start the query on the main thread
    dispatch_async(dispatch_get_main_queue(), ^{
        BOOL startedQuery = [self.query startQuery];
        if (!startedQuery)
        {
            NSLog(@"Failed to start query.\n");
            return;
        }
    });
}

Answer 2

You have to force any NSURL item to be cached in iCloud with this method:

- (BOOL)addBackupAttributeToItemAtURL:(NSURL *)URL
{
    NSLog(@"URL: %@", URL);
    assert([[NSFileManager defaultManager] fileExistsAtPath: [URL path]]);

    NSError *error = nil;
    BOOL success = [URL setResourceValue: [NSNumber numberWithBool: NO]
                                  forKey: NSURLIsExcludedFromBackupKey error: &error];
    return success;
}

You're need to launch this method on every directory and file you're downloading/creating in Documents or Library directory.

Answer 3

I don't believe that you have any control over when the sync will occur when using iCloud and core-data. With UIDocument and iCloud I have used startDownloadingUbiquitousItemAtURL with varying degrees of success but for core-data I don't think there is any equivalent -- I would love to hear someone tell me otherwise however...