Objective-C

Modern iOS/macOS Development: While Objective-C still works, Apple now recommends Swift for new projects. See the Swift example below.

Objective-C (Legacy)

+ (NSString *)GetUUID
{
  CFUUIDRef theUUID = CFUUIDCreate(NULL);
  CFStringRef string = CFUUIDCreateString(NULL, theUUID);
  CFRelease(theUUID);
  return [(NSString *)string autorelease];
}

Modern Objective-C (iOS 6.0+ / macOS 10.8+)

+ (NSString *)generateUUID
{
    return [[NSUUID UUID] UUIDString];
}

// Usage:
NSString *uuid = [[NSUUID UUID] UUIDString];
NSLog(@"UUID: %@", uuid);

Swift (Recommended for New Projects)

// Simple one-liner
let uuid = UUID().uuidString
print("UUID: \(uuid)")

// Or as a function
func generateUUID() -> String {
    return UUID().uuidString
}

source from stackoverflow.com

*NSUUID and Swift UUID conform to RFC 4122 UUID specification*