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What is the first responder?

Paul Hudson       @twostraws

Most of UIKit has a concept of responders baked deep into the system, but it’s not common you need to work with it directly. It’s Apple’s implementation of a design pattern called the Chain of Responsibility: UIKit asks one component if it can respond to an action, but if it can’t it gets passed to another component, and if that can’t respond then it gets passed on and on until something can respond – it’s a chain of responders.

The first responder is whatever control is currently ready to respond to actions. In UIKit this is usually the control that has activated the keyboard and is receiving input. If you want that text control to stop waiting for input – which in turn dismisses the keyboard – you should call its resignFirstResponder() method, which passes the first responder baton to the next waiting component.

The responder chain is how events bubble upwards on Apple platforms: touchesBegan() might be implemented on a view, on its view controller, on a parent view controller, or even higher up, but it will always be triggered somewhere when it happens.

Available from iOS 2.0 – learn more in my book Swift Design Patterns

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