Swift Delegate-Protocol example with SpriteKit

This is an example of delegation with SpriteKit.
SpriteKit is Apple's 2D Game Framework.
What i will show you is the how/when i use delegation.

I have 3 classes.

1- GameScene

This is the current scene of game. This is where all the object are interacting with each others.

GameScene.swift

import Foundation
import SpriteKit

class GameScene : SKScene
{
    // MARK:- PROPERTIES

    var playerController : PlayerController = PlayerController()

    // MARK:- INIT

    override func didMove(to view: SKView)
    {
        // GameScene loaded
    }

}

Player

This is my player sprite. This object holds all player animations.(move,attack,jump etc.)

Player.swift

import SpriteKit

class Player : SKSpriteNode
{
    func attack() 
    {
        // attack animation here
    }
}

PlayerController

This object is responsible for receiving user inputs and show some animations regarding of those user inputs.

PlayerController.swift

import Foundation

class PlayerController
{
    var player : Player = Player() // create player object

    func attackKeyPressed()
    {
        player.attack() // tell player object to run animation
    }
}

Let's say, user pressed the attack button.
This means PlayerController will call attack animation in Player object.
But now GameScene must know that an attack action happened because Player might hit something with that attack and other objects must change their values according to that action.

This is done by delegation.
To do it change PlayerController object to this:

import Foundation

class PlayerController
{
    var player : Player = Player() // create player object
    weak var delegate : PlayerControllerDelegate? // create delegate object (must be weak otherwise ARC won't deallocates)

    func attackKeyPressed()
    {
        player.attack() // tell player object to attack
        delegate?.playerDidAttack // GameScene will hear this
    }
}

protocol PlayerControllerDelegate: AnyObject // AnyObject for able to weak reference 
{
    func playerDidAttack() // delegate function
}

And change GameScene object to this:

import Foundation
import SpriteKit

class GameScene : SKScene, PlayerControllerDelegate
{
    // MARK:- PROPERTIES

    var playerController : PlayerController = PlayerController()

    // MARK:- INIT

    override func didMove(to view: SKView)
    {
        self.playerController.delegate = self // set delegate
    }

    // MARK:- DELEGATE FUNCTIONS

    func playerDidAttack()
    {
        print("player did attack")
        // do something when player attacks

    }
}

Now whenever an attack input entered by user. PlayerController will run Player object's attack animation and also tell GameScene that an attack happened. Then GameScene can tell other objects what they should do.

You can also download my prototype game Retrokid below.
(Use your keyboard w,a,s,d to walk and attack with k button.)

Retrokid App
Retrokid Source Code (.zip)
Retrokid Source Code (.tar.gz)

Blog

Swift Delegate-Protocol example with SpriteKit

Efe Ertugrul

1- GameScene

Player

PlayerController

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