How to check if iCloud is configured programmatically

Question

Here is the sentence from Apple Docs: "If iCloud is not configured, ask users if they want to configure it (and, preferably, transfer them to Launch Settings if they want to configure iCloud)."

How can I check if iCloud is configured or not and how to launch settings for iCloud?

Answer 1

Edit:
If you are targeting iOS6 or above you can use [[NSFileManager defaultManager] ubiquityIdentityToken];. For usage example please refer @Dj S' answer :).
It is faster and easier than the original solution which was meant for people targeting iOS5 and above

Original Answer
As documented in iOS App programming guide - iCloud Storage. That can be checked by asking the ubiquity container URL to the file manager :)

As long as you supply a valid ubiquity container identifier below method should return YES

- (BOOL) isICloudAvailable
{
    // Make sure a correct Ubiquity Container Identifier is passed
    NSURL *ubiquityURL = [[NSFileManager defaultManager] 
        URLForUbiquityContainerIdentifier:@"ABCDEFGHI0.com.acme.MyApp"];
    return ubiquityURL ? YES : NO;
}

However, I've found that URLForUbiquityContainerIdentifier: might take several seconds the very first time within a session (I used it in iOS5 so things might be different now). I remember using something like this:

dispatch_queue_t backgroundQueue = 
   dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_async(backgroundQueue,^{
   BOOL isAvailable = [self isICloudAvailable]
  /* change to the main queue if you want to do something with the UI. For example: */
   dispatch_async(dispatch_get_main_queue(),^{
       if (!isAvailable){
         /* inform the user */
         UIAlertView *alert = [[UIAlertView alloc] init...]
         [alert show];
         [alert release];
       }
   });
});