Apple Developer Documentation

Respond to events on behalf of a delegator.

• Delegator 를 대신해서 반응하다

Overview

You use delegates to interact with Cocoa objects that inform you of events in an app.

• delegate를 사용하여 앱의 이벤트를 알려주는 Cocoa object 와 상호 작용함.

Adopt a Delegate Protocol

Cocoa APIs often provide protocols that include delegate methods. When an event occurs—such as a user resizing a window—a class that's a delegator will detect the event and call delegate methods on the class you specify as the delegate. Delegate methods can customize how an app responds to an event.

The example below adopts the NSWindowDelegate protocol and implements its window(_:willUseFullScreenContentSize:) method:

• Cococa API는 delegator 메서드를 포함하는 프로토콜을 제공
• 사용자의 이벤트를 delegate 클래스가 감지하고 사용자가 delegator로 지정한 클래스의 메서드를 호출
• delegator 메서드는 앱이 이벤트에 응답하는 방식을 customizing 할 수 있음

class MyDelegate: NSObject, NSWindowDelegate {
		func window(_ window: NSWindow, willUseFullScreenContentSize proposedSize: NSSize) -> NSSize {
        return proposedSize
    }
}

Check That Delegates Exist

The Cocoa delegation pattern doesn't require that delegates are instantiated. If you don't need to respond to events, you don't need to create a delegate. Before you call a method on an object's delegate, make sure that the delegate isn't nil.

The example below creates an NSWindow and uses optional chaining to check that the window's delegate exists before sending a message to the delegate.

• Cocoa Delegate Pattern은 delegator가 인스턴스화 될 필요 없음
• 이벤트에 응답할 필요가 없으면 대리자를 만들 필요 없음

let myWindow = NSWindow(
    contentRect: NSRect(x: 0, y: 0, width: 5120, height: 2880),
    styleMask: .fullScreen,
    backing: .buffered,
    defer: false
)

myWindow.delegate = MyDelegate()
if let fullScreenSize = myWindow.delegate?.window(myWindow, willUseFullScreenContentSize: mySize) {
    print(NSStringFromSize(fullScreenSize))
}