Swift delegate design sample – The.Swift.Dev.

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 reviews a bug. The challenge supervisor creates a problem and tells one of many builders to repair the issue asap.

See? That is delegation. Sooner or later an occasion occurred, so the delegator (supervisor) utilized an exterior useful resource (a developer) utilizing a standard interface (situation describing the issue for each get together) to do obtain one thing (repair the 🐛).

To reveal how delegation works in actual life I made a fairly easy instance. I’ll use an analogous method (as a result of Xcode playgrounds are nonetheless freezing each 1-5 minutes) like I did for the command sample, however the goal of this one goes to be nearly totally totally 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) {
        swap enter {
        case "hello":
            print("🌎 Whats up world!")
        case "bye":
            print("👋 Bye!")
            exit(0)
        default:
            print("🔍 Command not discovered! Please strive once more:")
        }
    }
}

let inputHandler = InputHandler()
let inputReceiver = InputReceiver()
inputHandler.delegate = inputReceiver
inputHandler.pay attention()

That is how one can create your individual delegate sample in Swift. You possibly can think about that Apple is doing the identical factor below the hood, with UICollectionViewDataSource, UICollectionViewDelegate and so forth. You solely should 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 ought to be weak properies, otherwise you’ll create a very dangerous reatin 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 just a little bit and the property contained in the delegator. At all times use weak delegate variables if you will assign a category as a delegate. ⚠️

As you may see delegation is fairly simple, 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 superb articles about delegates, if you would like to know extra about this sample, it’s best to verify them out.