Who is part of the responder chain in iOS?

The responder chain in iOS consists of objects inheriting from UIResponder. These include:

• UIView (and its subclasses)
• UIViewController (and its subclasses)
• UIWindow (and its subclasses)
• UIApplication

The chain is constructed as follows:

• For View: the next responder is its superview or UIViewController, if the View is the root for the controller.
• For View Controller: the next responder is its view.superview (if any), or UIWindow if the controller is the root for the window, or UIApplication.
• For Window: the next responder is UIApplication.
• For Application: the next responder is nil (the chain ends).

The chain is used for handling events (such as touches, gestures, control actions) and commands (Actions). The event/command is passed from the first responder up the chain until one object handles it.

Example of a touch event passing:

1. The UIView where the touch occurred.
2. Its superview.
3. The next superview.
4. ...
5. The root UIView of the controller.
6. UIViewController.
7. UIWindow.
8. UIApplication.