Create a device-specific identifier in Objective-C

MyAppDelegate.m

@implementation MyAppDelegate

/**
 * Generates a Universally Unique Identifier based on the time and
 * hardware details of a device. CFUUIDCreate is the recommended
 * way by Apple to generate an ID now that UIDevice-uniqueIdentifier
 * is deprecated.
 *
 * Props: http://www.cocoabuilder.com/archive/cocoa/217665-how-to-create-guid.html#217668
 */
- (NSString *)getDeviceID
{
  static NSString *idKey = @"deviceId";
  NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
  NSString *uuid = [defaults objectForKey:idKey];
  if (!uuid) {
    CFUUIDRef uuidRef = CFUUIDCreate(NULL);
    CFStringRef uuidStringRef = CFUUIDCreateString(NULL, uuidRef);
    CFRelease(uuidRef);
    uuid = [NSString stringWithString:(NSString *) uuidStringRef];
    CFRelease(uuidStringRef);
    [defaults setObject:[uuid copy] forKey:idKey];
  }
  return uuid;
}

@end