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 shopper stories a bug. The undertaking 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 (subject describing the issue for each social gathering) to do obtain one thing (repair the 🐛).

To display how delegation works in actual life I made a reasonably easy instance. I will 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 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 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) {
        swap enter {
        case "hello":
            print("🌎 Good day 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.hear()

That is how one can create your individual delegate sample in Swift. You possibly can think about that Apple is doing the identical factor underneath the hood, with UICollectionViewDataSource, UICollectionViewDelegate and so on. 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 price to say that every one the category delegates ought to be weak properties, otherwise you’ll create a extremely 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 a bit of 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 may see delegation is fairly simple, 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 wonderful articles about delegates, if you would like to know extra about this sample, you need to test them out.