How do I add the UIApplicationDelegate to the end of the UIResponder chain?

Question

I'm trying to provide an IBAction method for common functionality that is required at various parts of the app.

i.e. Login is implemented modally, and if it succeeds results in a notification that allows all loaded view controllers to react to this event (transition from anonymous to authenticated)

@interface MyAppDelegate : NSObject <UIApplicationDelegate>
{
  ...
}
- (IBAction)loginTapped:(id)sender;
@end

I set the action of that button to the First Responder in IB, however the responder chain doesn't give MyAppDelegate a chance to respond.

My problem is that, I don't want to replicate the method at various parts of the responder chain, I would like to add it to a common class that is already a subclass.

The UIResponder chain goes all the way through to the UIApplication but that seems to be the end. My UIApplicationDelegate doesn't get to participate.

I want to insert or add my app delegate to the responder chain!

(or find another way to hook up the UIButton touch-up-inside to an app-wide implementation.. I want to avoid subclassing the UITabBarController or UIWindow if possible)

Answer 1

You could subclass UIApplication to have -nextResponder return the application delegate if it is a UIResponder subclass. You'll then need to alter your call to UIApplicationMain to use your custom subclass.

I haven't tried this myself, but I can't think of any immediate problems this would cause.

Answer 2

Starting with iOS 5, the AppDelegate is automatically the last link in the responder chain. Xcode project templates will create an AppDelegate that is a subclass of UIResponder rather than NSObject. However, to avoid cluttering up the AppDelegate, override the AppDelegate's nextResponder and offload work into a custom UIResponder object:

- (UIResponder *)nextResponder
{
    static dispatch_once_t onceToken;
    static LastUIResponder *lastResponder = nil;
    dispatch_once(&onceToken, ^{
        lastResponder = [[LastUIResponder alloc] init];
    });
    return lastResponder;
}