How to show an alert when we entered wrong secure code using Objective-C in iOS application

I have a webservices url which appends with securecode. When I enter correct securecode for example to say abcd, then application will load. when I entered wrong secure code, I need to show alert as 'wrong securecode'. My code is here:

- (void) alertStatus:(NSString *)msg :(NSString *)Title:(int)tag
{
    UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:Title

                                                    message:msg
                                                   delegate:self
                                          cancelButtonTitle:@"Ok"
                                          otherButtonTitles:nil, nil];
    if(tag) 
        alertView.tag = tag;
    [alertView show];
}


-(IBAction)loginClicked:(id)sender {

    @try {

        if([[txtsecurecode text] isEqualToString:@""]  ) {
            [self alertStatus:@"Please enter Access code" :@"Login Failed!":0];
        } else {
            NSString *post =[[NSString alloc] initWithFormat:@"txtsecurecode=%@",[txtsecurecode text]];

            NSURL *url=[NSURL URLWithString:[NSString stringWithFormat:@"http://my example.com/Accountservice/Security/ValidAccess?accesscode=%@&type=1",txtsecurecode.text]];

            NSString *responseData = [[NSString alloc]initWithData:[NSData dataWithContentsOfURL:url] encoding:NSUTF8StringEncoding];

responseData is the reference where I am getting response from the web services url.so below getting response, I need to keep alert.

How can I keep alert in this case showing alert when entered wrong secure code?

Try to use this code...

-(IBAction)loginClicked:(id)sender {

    @try {

        if([[txtsecurecode text] isEqualToString:@""]  ) {
            [self alertStatus:@"Please enter Access code" :@"Login Failed!":0];
        } else {
            NSString *post =[[NSString alloc] initWithFormat:@"txtsecurecode=%@",[txtsecurecode text]];

            NSURL *url=[NSURL URLWithString:[NSString stringWithFormat:@"http://my example.com/Accountservice/Security/ValidAccess?accesscode=%@&type=1",txtsecurecode.text]];


            /*UPDATED*/
            NSString *responseData = [[NSString alloc]initWithContentsOfURL:[NSData dataWithContentsOfURL:url] encoding:NSUTF8StringEncoding error:nil];


            if([responseData isEqualToString:@""])
            {
                [self alertStatus:@"Please enter valid Access code" :@"Login Failed!":0];
            }
            else
            {
                //Your code for handling the response data
            }
        }
    }
}