· 1 min learn
The delegate design sample is a comparatively straightforward approach to talk between two objects by way of a standard interface, protocol in Swift.
Implementing delegation in Swift
You’ll 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 undertaking supervisor creates a problem and tells one of many builders to repair the issue asap.
See? That’s delegation. Sooner or later an occasion occurred, so the delegator (supervisor) utilized an exterior useful resource (a developer) utilizing a standard interface (problem describing the issue for each occasion) to do obtain one thing (repair the 🐛).
To show how delegation works in actual life I made a reasonably easy instance. I’m going to make use of an analogous strategy (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 completely 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 depart simply inform me "bye":")
}
func didReceive(enter: String) {
change enter {
case "hello":
print("🌎 Whats up 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’ll be able to think about that Apple is doing the identical factor below the hood, with UICollectionViewDataSource, UICollectionViewDelegate and many others. You solely need to implement the delegate, they’ll present the protocol and the delegator. 🤔
Weak properties, delegates and courses
Reminiscence administration is a vital factor so it’s price to say that each one the category delegates must be weak properties, otherwise you’ll create a very dangerous 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 alter 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 standard interface that can be utilized by anybody who implements the delegate (generally information supply) protocol. There are actually wonderful articles about delegates, when you’d wish to know extra about this sample, you must test them out.
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