NSFileWrapper fails when from iCloud and works from local directory

Question

I have a problem syncing NSFileWrapper documents with iCloud. I am able to create my wrapper and save it to my ubiquitous container.

When I try to read it from the device that created it, it works. When I try to read form another device that got it from iCloud, it crashes.

Some code:

This function to add a wrapper container with a NSString

- (void) addNSString:(NSString*)_string toFileWrapper:(NSFileWrapper*)_wrapper forKey:(NSString*)_key {

    NSData *data = [NSKeyedArchiver archivedDataWithRootObject:_string];

    if(data) {

        [_wrapper addRegularFileWithContents:data preferredFilename:_key];
    }

}

And then here is how I decode it:

- (id) unarchiveObjectFromWrappers:(NSDictionary*)_wrappers withKey:(NSString*)_key {

    id value = nil;

    NSFileWrapper *wrapper = [_wrappers valueForKey:_key];
    if(wrapper) {

        NSData *data = [wrapper regularFileContents];

        if(data) {

            value = [NSKeyedUnarchiver unarchiveObjectWithData:data];
        }
    }

    return value;
}

The decoding part works on one device and not on the others (EXC_BAD_ACCESS when the NSKeyedUnarchiver tries to unarchive from the NSData. The NSData seems good, it has the proper length and everything but when I try to log its datas for example it crashes).

My guess is that the NSFileWrapper doesn't download its full content, only its structure and that I have to do something to make it available. But I don't know what.

Any ideas?

========

Edit:

NSURLUbiquitousItemIsDownloadedKey says that the file is downloaded BUT if I try to copy it to the sandbox it fails with this error: "The operation couldn’t be completed. Bad file descriptor"

So the file is either not uploaded properly to iCloud or not downloaded properly...

I'm facing a similar problem if I try to read the ubiquitous container (the iCloud Documents folder) with NSFileManager. If I access it after running a NSMetadataQuery, I can access the files. So I guess, you access the files directly with NSFileManager? — auco, Feb 19 '13 at 09:52
Thomas, maybe this is your case: http://stackoverflow.com/questions/8714525/cannot-sync-simple-text-file-with-icloud-bad-file-descriptor — brigadir, Apr 15 '13 at 21:01

score 1 · Answer 1 · edited May 23 '17 at 11:56

It drove me crazy too. The solution is rather simple, yet totally undocumented by Apple. You must download the file specifically. Only the file wrapper is downloaded automatically, but not its contents. That's why the check says the file exists.

Before copying the file over, call something like this:

[[NSFileManager defaultManager]startDownloadingUbiquitousItemAtURL:cloudURL error:nil];

Related: Cannot sync simple text file with iCloud (bad file descriptor)

NSFileWrapper fails when from iCloud and works from local directory

1 Answers1