I want touch the UIBarButtonItem in the top right, and push a new viewController. So, the code is:
UIBarButtonItem *addButton = [[UIBarButtonItem a
Since you have added your vc in storyboard, hence initWithNibName will not work.
Either use segue or use storyboard's method instantiateViewControllerWithIdentifier to instantiate the view controller
Use this code it works for you
UIStoryboard *mainStoryboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
yourViewController *vc = [mainStoryboard instantiateViewControllerWithIdentifier:@"chosenCountry"];
[self.navigationController pushViewController:vc animated:YES];
UIStoryboard *sb = [UIStoryboard storyboardWithName:@"MainStoryboard" bundle:nil];
UIViewController *vc = [sb instantiateViewControllerWithIdentifier:@"chosenCountry"];
[self.navigationController pushViewController:vc animated:YES];