How does iOS know which view controller should be active?

Question

If I want to replace one screen of an app with another, but I don't use a navbar/tabbar controller, then I could just remove oldViewController.view from window and add newViewController.view to it. That's all, now newViewController will get rotation events, etc.

But UIView does not reference "its" controller, so how is this possible, how iOS know it should make newViewController an active one? Does iOS do some magic, it internally references controller from view or what?

UPDATE:

I think I was misunderstood: I don't ask how to make some view controller an active one - I know that. I'm just curious, how is it possible that I pass some view to UIWindow object ([window addSubview:view]) and it somehow finds view controller although view doesn't know its controller.

Answer 1

yeh I had the same question like you. and I figured it out.

UIView is derived from UIResponder. and UIView must subclass UIResponder::nextResponder.

Its default implementation is returning a view controller of the view (if it hadn't, it would be super view)

So, consequently view can see its controller. that means window know the topmost view and also

its controller.

good luck.

Answer 2

Unfortunately, iOS only send events to the first ViewController of the stack. You can try and present a new one on the top of others with video for example, it will never rotate.

If you don't use navbar/tabbar controller you will have to add and remove everytime from the Window to keep only one at the time if you wand to have events.

Answer 3

The main UIWindow class for your application will have a view controller set in its rootViewController property. That controller's view is the "main" view for the app. This is usually setup in the main .xib for the project. That view controller will receive the usual events like "viewDidAppear" or "willRotateToInterfaceOrientation". You can put up your own view over top of it if you want to, but you will need to manage those events yourself. Usually you don't do that though. You just use a UINavigationController or UITabBarController as your rootViewController and allow them to manage getting the events to new "pushed" view controllers, or you popup view controllers with "presentModalViewController".