Can you explain the mechanism of UIResponder in the iOS event handling system?

In iOS, UIResponder is the base class responsible for handling events such as touches, key presses, movements, and other user interactions. The mechanism is based on the responder chain. When an event occurs, it is passed to the first UIResponder object that can handle it (for example, a UIView or UIViewController). If the object does not handle the event, it is passed to the next object in the chain — usually a parent element or controller.

This allows for flexible distribution of event handling among different interface objects, providing a convenient way to respond to user actions without needing to directly connect all objects.

An example of a responder chain:

UIView (button) → UIView (container) → UIViewController → UIWindow → UIApplication

If the button does not handle the event, it is passed further along the chain.