IPhone : how to retrieve Nsstring value from Nsobject?

i have small doubt in retrieve value from Nsobject class.Firstly i handling login check condition, when i press login button i get response from web service in Nslog, in that i have to capture a string called LoginStatus wether its success r failure.i created NSObject class and its contains one one String,my NSObject class name response_value

@property (nonatomic, retain)NSString *Loginstatus;

now in web service class:

response.Loginstatus =[[[json valueForKey:@"login_response"]valueForKey:@"status"]objectAtIndex:0];

NsLog (@"%@",response.Loginstatus);

my requested string values are stored in response.LoginStatus string successfully.

But my actual problem is stating in my Login ViewController

i set an condition to check login status if login success means i need to show alert msg either for success r for failure

response_value *response = [[response_value alloc]init];
if ([response.response.Loginstatus isEqualToString:@"Login Successfull"]) {
        UIAlertView *alert = [[UIAlertView alloc]initWithTitle:@"Success" message:response.loginStatusString delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil, nil];
        [alert show];
    }

but this condition never getting called and i also checked wether the NSObject string holds any values but the values are null in Nslog

can someone fix my problem