Swift delegate design sample – The.Swift.Dev.

Implementing delegation in Swift

You’ll want a delegate protocol, a delegator who truly 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 experiences a bug. The mission supervisor creates a difficulty 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 (difficulty 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’m going to make use of 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 function of this one goes to be virtually completely 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 hear() {
        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) {
        change enter {
        case "hello":
            print("🌎 Good day 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.hear()

That is how one can create your individual delegate sample in Swift. You’ll be able to think about that Apple is doing the identical factor underneath the hood, with UICollectionViewDataSource, UICollectionViewDelegate and so on. You solely need to implement the delegate, they’ll present the protocol and the delegator. 🤔

Weak properties, delegates and lessons

Reminiscence administration is an important factor so it’s value 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 vary your protocol slightly bit and the property contained in the delegator. At all times use weak delegate variables if you’re going to assign a category as a delegate. ⚠️

As you possibly can 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 (typically knowledge supply) protocol. There are actually wonderful articles about delegates, in case you’d wish to know extra about this sample, you must examine them out.