Implementing delegation in Swift
You will want a delegate protocol, a delegator who really delegates out the duties and a delegate object that implements the delegate protocol and does the precise work that was requested by the “boss”. Let’s translate this into human.
The consumer studies a bug. The challenge supervisor creates a difficulty and tells one of many builders to repair the issue asap.
See? That is delegation. In some unspecified time in the future an occasion occurred, so the delegator (supervisor) utilized an exterior useful resource (a developer) utilizing a typical interface (problem describing the issue for each celebration) to do obtain one thing (repair the 🐛).
To display how delegation works in actual life I made a fairly easy instance. I’ll use the same method (as a result of Xcode playgrounds are nonetheless freezing each 1-5 minutes) like I did for the command sample, however the objective of this one goes to be virtually totally completely different, as a result of we’re speaking about delegation. 😅
#!/usr/bin/env swift
import Basis
protocol InputDelegate {
var shouldContinueListening: Bool { get }
func didStartListening()
func didReceive(enter: String)
}
class InputHandler {
var delegate: InputDelegate?
func pay attention() {
self.delegate?.didStartListening()
repeat {
guard let enter = readLine() else {
proceed
}
self.delegate?.didReceive(enter: enter)
}
whereas self.delegate?.shouldContinueListening ?? false
}
}
struct InputReceiver: InputDelegate {
var shouldContinueListening: Bool {
return true
}
func didStartListening() {
print("👻 Please be good and say "hello", if you wish to go away simply inform me "bye":")
}
func didReceive(enter: String) {
swap enter {
case "hello":
print("🌎 Howdy world!")
case "bye":
print("👋 Bye!")
exit(0)
default:
print("🔍 Command not discovered! Please attempt once more:")
}
}
}
let inputHandler = InputHandler()
let inputReceiver = InputReceiver()
inputHandler.delegate = inputReceiver
inputHandler.pay attention()That is how one can create your personal delegate sample in Swift. You possibly can think about that Apple is doing the identical factor below the hood, with UICollectionViewDataSource, UICollectionViewDelegate and so on. You solely need to implement the delegate, they will present the protocol and the delegator. 🤔
Weak properties, delegates and lessons
Reminiscence administration is an important factor so it is value to say that each one the category delegates needs to be weak properties, otherwise you’ll create a very unhealthy retain cycle. 😱
protocol InputDelegate: class { }
class InputHandler {
weak var delegate: InputDelegate?
}
class InputReceiver: InputDelegate {
}Right here is the altered Swift code snippet, however now utilizing a category because the delegate. You simply have to vary your protocol slightly bit and the property contained in the delegator. All the time use weak delegate variables if you’re going to assign a category as a delegate. ⚠️
As you may see delegation is fairly straightforward, however it may be harmful. It helps decoupling by offering a typical interface that can be utilized by anybody who implements the delegate (typically information supply) protocol. There are actually wonderful articles about delegates, if you would like to know extra about this sample, it is best to examine them out.
