Create a unique string used for saving data

Question

I'm building an application for the iphone. I scan the iPod library and bring in all the album art. I need a way of creating a unique string so that when I'm saving the album art to the documents directory, each file has a unique name. Does anyone know to create a unique string? Thanks in advance.

Answer 1

I use this code:

+ (NSString *)getUniqueFilenameInFolder:(NSString *)folder forFileExtension:(NSString *)fileExtension {
    NSFileManager *fileManager = [NSFileManager defaultManager];
    NSArray *existingFiles = [fileManager contentsOfDirectoryAtPath:folder error:nil];
    NSString *uniqueFilename;

    do {
        CFUUIDRef newUniqueId = CFUUIDCreate(kCFAllocatorDefault);
        CFStringRef newUniqueIdString = CFUUIDCreateString(kCFAllocatorDefault, newUniqueId);

        uniqueFilename = [[folder stringByAppendingPathComponent:(NSString *)newUniqueIdString] stringByAppendingPathExtension:fileExtension];

        CFRelease(newUniqueId);
        CFRelease(newUniqueIdString);
    } while ([existingFiles containsObject:uniqueFilename]);

    return uniqueFilename;
}

Maybe it helps someone. :-)

Keep in mind, that this returns the full path of the unique file. You might want to add some small changes to just return the filename. For example if you want to persist it somewhere.

Answer 2

You want to be creating a GUID or UUID, which is a 128-bit integer that has a string associated with it. Check out http://developer.apple.com/library/ios/#documentation/CoreFoundation/Reference/CFUUIDRef/Reference/reference.html