What is the role and functioning principle of the event handler chain in the interface system?

In iOS, the interface event system uses a responder chain to pass events from the source to the final receiver. This is a sequence of objects (usually UIView, UIViewController, UIWindow) that can handle an event, such as a touch or gesture.

How it works:

• When an event occurs (for example, a screen touch), it is first directed to the first object in the chain — usually the lowest UIView where the event occurred.
• If this object does not handle the event (does not implement the corresponding method or explicitly passes it on), the event is passed to the next object in the chain — for example, the parent UIView.
• The chain continues upward through the hierarchy until the event is handled or it reaches the top level (usually UIWindow).

The role of the responder chain is to provide flexible hierarchical routing of events, allowing different objects to respond to events without tight coupling. This simplifies architecture and increases component reusability.

Example:

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    if canHandleTouch {
        // Handle the event
    } else {
        super.touchesBegan(touches, with: event) // Pass it further along the chain
    }
}