Can you give an example of a situation where the protocol principle is applied?

The protocol principle in iOS is used when you need to define a set of requirements (methods, properties) that a class or structure must implement without specifying the exact implementation.

For example, if you have different types of objects that need to respond to a button press, you can create a protocol:

protocol ButtonActionDelegate {
    func didTapButton()
}

class ViewController: UIViewController, ButtonActionDelegate {
    func didTapButton() {
        print("Button tapped")
    }
}

This approach allows for writing flexible and extensible code, where different objects can implement the same protocol in their own way.