Copy iCloud file to sandbox

Question

I'm looking for a better way to download a bunch of files from my iCloud container to my sandbox. This is what I currently use:

for (FileAttachments *fileLink in items) {
        NSURL *cloudFileURL = [fileLink urlForCloudAttachmentWithName];

        NSURL *fileURL = [backupCloudLocalDirectoryURL URLByAppendingPathComponent: fileLink.fileName];

        NSFileCoordinator *fileCoordinator = [[NSFileCoordinator alloc] initWithFilePresenter:nil];

        [fileCoordinator coordinateReadingItemAtURL:fileURL options:NSFileCoordinatorReadingWithoutChanges error:&error

                                             byAccessor:^(NSURL *newURL) {

                   NSError *blockError = nil;

                   [fileManager copyItemAtURL:cloudFileURL toURL:fileURL error:&blockError];
                                }];
        }
}

Is there any problem with making a copy of the iCloud item this way? In production, I have some users complaining that all their files weren't downloaded. Is it better to use NSFileManager's startDownloadingUbiquitousItemAtURL:error instead? If so, why? Thanks.

Answer 1

It's still not completely clear to me from comments how you're discovering the URLs, however some important details that affect your situation are:

1. Using coordinateReadingItemAtURL:block: has nothing to do with downloading files from iCloud. The purpose of NSFileCoordinator is to coordinate among readers and writers of a file so that, for example, you don't get two threads trying to write to the same file at the same time. You use file coordinators with iCloud because the iCloud system needs to read and write files and so does your app. Using a coordinator avoids corrupting the file, but again, has nothing to do with downloading the file.

2. To download a file from iCloud you need to use startDownloadingUbiquitousItemAtURL:error: and then wait until the file downloads. The normal flow here is:

   a. Use NSMetadataQuery to find files that exist in the iCloud account

   b. Use startDownloadingUbiquitousItemAtURL:error: to make sure they're available on the local device.

   The reason you need to use this call is simply because that's how iCloud works on iOS. Files don't download until you ask them to download, and this is how you ask. [On OS X it's different, everything automatically downloads.]

3. You cannot simply copy from an iCloud URL to another location unless you already know that the file has been downloaded. The file-copy operation does not download the file, so if the file isn't available locally, the copy will fail.

Answer 2

You must use a metadata query to identify the files and their download status then, if they have not been downloaded initiate the download, and using the metadata query determine when the download is complete and then copy the file from the ubiquity container to the apps sandbox directory using a file coordinator. If you try copying the file while it's partially downloaded you may get some strange results.

Answer 3

I had the same problem with you.

My case is that: When network disconnects, iCloud service copy file from iCloud container to sandbox. When this line executes, it can not go into the block to copy file. This is the reason why this file can not be copied.

fileCoordinator coordinateReadingItemAtURL:fileURL options:NSFileCoordinatorReadingWithoutChanges error:&error byAccessor:^(NSURL *newURL)

My solution is: Before copying file from iCLoud container to sandbox, you must check network. If it is not available, don't execute this code (return method). If network connects, execute fileCoordinator and copy.

More info: When copy file from ICloud container to sandbox, method fileManager copyItemAtURL:toURL:error: is OK because I implement this method and it's good.

Hope this works.