iCloud: Callback for NSFileManager's startDownloadingUbiquitousItemAtURL?

问题

I am using NSFileManager's startDownloadingUbiquitousItemAtURL to download file from iCloud to local copy (the local does not yet have the copy of the file in this case). I can't seem to find the callback for this process. I need the callback to tell my app that the requested file is finished downloaded (to local copy) so other task can start reading the content of the file and does stuff.

I can check to see if the file is downloaded. But it would involve in polling constantly. Is there a way to do this without setting a timer to poll for this?

回答1:

I believe that this method is intended to be used in conjunction with file coordinators based on Apple's documentation. So you would need to use a file coordinator like so:

NSURL *itemURL = nil; // this is the URL you want to read from

__block NSData *data = nil;
NSError *error = nil;
NSFileCoordinator *coordinator = [[NSFileCoordinator alloc] initWithFilePresenter:nil];
[coordinator coordinateReadingItemAtURL:itemURL options:0 error:&error byAccessor:^(NSURL *newURL) {
    data = [NSData dataWithContentsOfURL:newURL];
}];

This will be synchronous, however, so if you wanted to do something asynchronously, you could use blocks as so:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    // read info from the URL using the code above
    dispatch_async(dispatch_get_main_queue(), ^{
        // handle data read from the URL
    });
});

回答2:

To upload correctly to iCloud you're going to also need something like this (anything else didn't work :| )

   NSURL *ubiq = [[NSFileManager defaultManager] URLForUbiquityContainerIdentifier:nil];

   NSString *FileNS = @"myfile.dat";
   NSURL *FileURL = [[ubiq URLByAppendingPathComponent:@"Documents"] URLByAppendingPathComponent:FileNS ];


   BYTE *data = NULL;//Put your file data in here
   int FileSize = 0;//replace with your file size
   NSData *myData = [[NSData alloc] initWithBytes:data length:FileSize];
   [myData writeToFile:[FileURL path] atomically:YES];

来源：https://stackoverflow.com/questions/9675303/icloud-callback-for-nsfilemanagers-startdownloadingubiquitousitematurl

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