Adding an enemy every 10 seconds which tracks your location

Question

Below I have part of the code for a simple game I am making. in the game, your finger around the screen a ball is underneath your finger. Then every 10 seconds a ball gets added in which follows your ball. I have an SKAaction which calls my add enemy function every 10 seconds which spawns the enemy. The issue is that I can't make the add enemy function update every frame because the SKAction won't let me call it if its updating every frame, so I'm not sure what to do in order for the the ball to be added in every 10 seconds and to have that ball track your location. Because currently it only tracks the initial location of the ball when it was added in. any help is appreciated, thank you.

import SpriteKit
import GameplayKit

class GameScene: SKScene {

    var me = SKSpriteNode()

    override func didMove(to view: SKView) {

        me = self.childNode(withName: "me") as! SKSpriteNode

        let border = SKPhysicsBody (edgeLoopFrom: self.frame)
        border.friction = 0
        self.physicsBody = border

        run(SKAction.repeatForever(SKAction.sequence([SKAction.run(createEnemy), SKAction.wait(forDuration: 10.0)])))
    }

    func createEnemy () {

        let enemy = SKSpriteNode(imageNamed: "ball 1")
        enemy.name = "enemy"
        enemy.position = CGPoint(x:667, y: -200)

        enemy.run(SKAction.moveTo(x: me.position.x, duration: 2))
        enemy.run(SKAction.moveTo(y: me.position.y, duration: 2))

        enemy.zPosition = +1
        addChild(enemy)
    }

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {

        for touch in touches{

            let location = touch.location(in: self)
            me.run(SKAction.moveTo(x: location.x, duration: 0))
            me.run(SKAction.moveTo(y: location.y, duration: 0))
        }
    }

    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {

        for touch in touches{

            let location = touch.location(in: self)
            me.run(SKAction.moveTo(x: location.x, duration: 0))
            me.run(SKAction.moveTo(y: location.y, duration: 0))
        }
    }

    override func update(_ currentTime: TimeInterval) {


    }
}

Answer 1

1. Keep a list of all of your currently alive enemies in a dictionary via their .name property. The values in this dictionary are a tuple. This tuple keeps track of the enemy's instance, and its target's instance.

I do this in your createEnemy via makeEnemyName and addEnemyToDict

2. during update give each enemy a new action to follow its target. This is done by iterating through the dictionary, then using each key's value to moveFollowerToTarget. This information is stored in the tuple type we created.

---

import SpriteKit

class GameScene22: SKScene {
  // MARK: - My code:

  // Tuple to keep track of enemy objects:
  typealias FollowerAndTarget = (follower: SKSpriteNode, target: SKSpriteNode)

  // [followerName: (followerSprite, targetSprite):
  var spriteDictionary: [String: FollowerAndTarget] = [:]

  // Give each enemy a unique name for the dictionary:
  var enemyCounter = 0

  // Assign to each enemy a unique name for the dictionary:
  private func makeEnemyName() -> String {
    enemyCounter += 1
    return "enemy\(enemyCounter)"
  }

  private func addEnemyToDict(enemy: SKSpriteNode, target: SKSpriteNode) {
    if let name = enemy.name { spriteDictionary[name] = (enemy, target) }
    else { print("enemy not found") } // error!
  }

  private func removeEnemyFromDict(enemy: SKSpriteNode) {
    if let name = enemy.name { spriteDictionary[name] = nil }
    else { print("enemy not removed from dictionary!") } // error!
  }

  // Note, you did not set the enemy to have a constant speed, so the enemy will move at random speeds
  // based on how far they are away from the target.
  private func moveFollowerToTarget(_ sprites: FollowerAndTarget) {
    let action = SKAction.move(to: sprites.target.position, duration: 2)
    sprites.follower.run(action)
  }

  private func allEnemiesMoveToTarget() {
    for sprites in spriteDictionary.values {
      moveFollowerToTarget(sprites)
    }
  }

  // Use this carefully if you are using phsyics later on:
  func killEnemy(_ enemy: SKSpriteNode) {

    // Remove this enemy from the update loop:
    removeEnemyFromDict(enemy: enemy)
    enemy.removeAllActions()
    enemy.removeFromParent()
    enemy.physicsBody = nil
  }

  // MARK: - Your code (mostly):

  var me = SKSpriteNode()

  override func didMove(to view: SKView) {
    me = SKSpriteNode(color: .blue, size: CGSize(width: 50, height: 50))
    me.name = "me"
    addChild(me)

    self.anchorPoint = CGPoint(x: 0.5, y: 0.5)
    let border = SKPhysicsBody (edgeLoopFrom: self.frame)
    border.friction = 0
    self.physicsBody = border

    run(SKAction.repeatForever(SKAction.sequence([SKAction.run(createEnemy), SKAction.wait(forDuration: 10.0)])))
  }

  func createEnemy () {

    let enemy = SKSpriteNode(color: .purple, size: CGSize(width: 30, height: 30))
    enemy.name = makeEnemyName()
    addEnemyToDict(enemy: enemy, target: me)

    moveFollowerToTarget((follower: enemy, target: me))
    enemy.zPosition = +1
    addChild(enemy)
  }

  override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {

    for touch in touches{

      let location = touch.location(in: self)
      me.run(SKAction.moveTo(x: location.x, duration: 0))
      me.run(SKAction.moveTo(y: location.y, duration: 0))
    }
  }

  override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {

    for touch in touches{

      let location = touch.location(in: self)
      me.run(SKAction.moveTo(x: location.x, duration: 0))
      me.run(SKAction.moveTo(y: location.y, duration: 0))
      allEnemiesMoveToTarget()
    }
  }

  override func update(_ currentTime: TimeInterval) {
    // Will iterate through dictonary and then call moveFollowerToTarget()
    // thus giving each enemy a new movement action to follow.
    allEnemiesMoveToTarget()
  }
}