handle error by inheriting viewcontrollers

LoginViewController.m

@interface LoginViewController : ParentViewController ()

@end

// ...

@implementation

#pragma mark LoginServiceDelegate
-(void)loginDidFailWithError:(NSError *)loginError
{
   [self handleError:loginError];
}

// overwrite error handling
-(void)handleError:(NSError *)error
{
   if (error.code == INVALIDE_PASSWORD_ERROR_CODE)
   {
      // manage invalid password error case...
      return;
   }

   [super handleError:error];
}

//...

@end

ParentViewController.m

@interface ParentViewController : UIViewController ()

-(void)handleError:(NSError *)error;

@end

//...

@implementation ParentViewController

-(void)handleError:(NSError *)error
{
   NSLog(@"%@",[error localizedDescription]);

   NSString *message;

   if (error.code == CUSTOM_NETWORK_ERROR_CODE)
   { // handle specific error kind
      message = @"Network Error";
   }
   else if (error.code == KNOWN_SERVER_ERROR_CODE)
   { // known error to display as if from the server
      message = error.domain;
   }
   else
   { //generic error message
      message = @"Something went wrong";
   }

   UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error"
                                                   message:message
                                                  delegate:nil
                                         cancelButtonTitle:@"OK"
                                          otherButtonTitle:nil];
}

//...

@end