iOS 获取全局唯一标示符

 NSString *identifier = [[NSProcessInfo processInfo] globallyUniqueString];
        NSLog(@"identifier1 ====== %@",identifier);
        identifier = [[NSProcessInfo processInfo] globallyUniqueString];
        NSLog(@"identifier2 ====== %@",identifier);
        identifier = [[NSProcessInfo processInfo] globallyUniqueString];
        NSLog(@"identifier3 ====== %@",identifier);
        identifier = [[NSProcessInfo processInfo] globallyUniqueString];
        NSLog(@"identifier4 ====== %@",identifier);