Swift delegate design sample – The.Swift.Dev.

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 experiences a bug. The mission 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 typical interface (difficulty describing the issue for each get together) 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 goal of this one goes to be nearly solely 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 go away simply inform me "bye":")
    }

    func didReceive(enter: String) {
        swap enter {
        case "hello":
            print("🌎 Hiya 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 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 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 every one the category delegates ought to 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 somewhat bit and the property contained in the delegator. All the time use weak delegate variables if you’ll assign a category as a delegate. ⚠️

As you possibly can 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 (generally knowledge supply) protocol. There are actually superb articles about delegates, for those who’d prefer to know extra about this sample, it’s best to examine them out.