You've created a UIViewController
object, which doesn't have a txtBtn
property.
You need to change from this line:
UIViewController *controller = [[UIViewController alloc] initWithNibName:@"XIBViewController" bundle:[NSBundle mainBundle]];
To this:
XIBViewController *controller = [[XIBViewController alloc] initWithNibName:@"XIBViewController" bundle:[NSBundle mainBundle]];
You'll also need to #import XIBViewContoller.h
in your AppDelegate.