Allow multiple instances of an SKAction - ios

Question

I am trying to create a "Space Invaders" game in swift, when the user touches the screen a bullet is shot from the ship, but when I try to touch it again while the bullet is moving across the screen I have an NSException and the game breaks. How do I set up the action so that there can be multiple instances of the action, so that the shooter is semi automatic. Below is my current scene controller.
import SpriteKit
class GameScene: SKScene {
let background = SKSpriteNode(imageNamed: "background")
let heroShip = SKSpriteNode(imageNamed: "heroShip")
let bullet = SKSpriteNode(imageNamed: "bullet")
override func didMoveToView(view: SKView) {
/* Setup your scene here */
background.position = CGPointMake(CGRectGetMidX(self.frame),CGRectGetMidY(self.frame))
heroShip.position = CGPointMake(self.size.width/6.0, self.size.height/2.0)
self.heroShip.zPosition = 1.0
self.addChild(background)
self.addChild(heroShip)
}
override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
bullet.position = CGPointMake(heroShip.position.x + bullet.size.width/2, heroShip.position.y)
let action = SKAction.moveToX(self.frame.width + self.bullet.size.width, duration: 0.5)
self.addChild(bullet)
bullet.runAction(action, completion: {
self.bullet.removeAllActions()
self.bullet.removeFromParent()
})
}
override func update(currentTime: CFTimeInterval) {
/* Called before each frame is rendered */
}
}

Answer 1

If you want to have multiple bullets shot from one ship, you have to create multiple instances of a bullet. What you have now is bullet property of GameScene class which is a mistake.
You probably want to instantiate bullets dynamically in your IBAction
So try something like this:
override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
let bullet = SKSpriteNode(imageNamed: "bullet")
bullet.position = CGPointMake(heroShip.position.x + bullet.size.width/2, heroShip.position.y)
let action = SKAction.moveToX(self.frame.width + bullet.size.width, duration: 0.5)
self.addChild(bullet)
bullet.runAction(action, completion: {
bullet.removeAllActions()
bullet.removeFromParent()
})
}
and remove
let bullet = SKSpriteNode(imageNamed: "bullet")
from the top of the class