关于UIAlertView按钮到其他视图控制器

在应用中有一个uialertview，有两个按钮，第一个是取消按钮，另一个是OK按钮，在按下OK按钮时，应该跳到一个带有storyboard标志符的视图控制器RootView。应该怎么实现？

- (void)showAlarm:(NSString *)text {
        UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"show alarm"
                                                            message:text delegate:self                                                  cancelButtonTitle:@"cancel"
                                                  otherButtonTitles:@"ok", nil];
        [alertView show];
    }
    - (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex{
        if (buttonIndex == 0){
             NSLog(@"cancel"); 
        }else if (buttonIndex == 1){
             NSLog(@"ok");
           UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"MainStoryboard_iPhone" bundle:[NSBundle mainBundle]];
           UINavigationController *navigationController = [storyboard instantiateViewControllerWithIdentifier:@"navigationController"];
            [navigationController presentViewController:[storyboard instantiateViewControllerWithIdentifier:@"RootView"] animated:YES completion:nil];
   }
    }