Generate an infinite amount of nodes and destroy by clicking on them - ios

Question

I want to generate an infinite amount of nodes that fall from the top of the screen and destroy them by just clicking on them, it is simple but I am having serious problems with it. When the nodes are generated by the loop I can only generate one and it starts moving instead of falling vertically. It also disappears and appears constantly.
Here is my code, hope you can help.
Thank you!!
import SpriteKit
class DestroyScene: SKScene , SKPhysicsContactDelegate{
var velocity:CGFloat = 0
let scoreText = SKLabelNode(fontNamed: "Arial Rounded MT Bold")
var score = 0
var lastYieldTimeInterval:NSTimeInterval = NSTimeInterval()
var lastUpdateTimerInterval:NSTimeInterval = NSTimeInterval()
var gameOver = false
var alien:SKSpriteNode = SKSpriteNode(imageNamed: "circuloAzulArt")
override func didMoveToView(view: SKView) {
self.physicsWorld.contactDelegate = self
self.physicsWorld.gravity = CGVectorMake(0, -velocity)
}
func addAlien(){
var alien:SKSpriteNode = SKSpriteNode(imageNamed: "circuloAzulArt")
alien.name = "alien"
alien.physicsBody = SKPhysicsBody(circleOfRadius: alien.size.width/2)
alien.physicsBody?.dynamic = true
var actionArray:NSMutableArray = NSMutableArray()
var actionArray2:NSMutableArray = NSMutableArray()
alien.removeFromParent()
if gameOver == false{
let minX = alien.size.width/2
let maxX = self.frame.size.width - alien.size.width/2
let rangeX = maxX - minX
let position:CGFloat = CGFloat(arc4random()) % CGFloat(rangeX) + CGFloat(minX)
alien.position = CGPointMake(position, self.frame.size.height + alien.size.height)
self.addChild(alien)
let minDuration = 3
let duration = Int(minDuration)
actionArray.addObject(SKAction.moveTo(CGPointMake(position, -alien.size.height), duration: NSTimeInterval(duration)))
actionArray.addObject(SKAction.removeFromParent())
alien.runAction(SKAction.sequence(actionArray))
}
}
func updateWithTimeSinceLastUpdate(timeSinceLastUpdate:CFTimeInterval){
var randomNum = Double(arc4random_uniform(20))
var xTime = ((randomNum / 20) + 0.25)
lastYieldTimeInterval += timeSinceLastUpdate
if (lastYieldTimeInterval > xTime){
lastYieldTimeInterval = 0
randomNum = Double(arc4random_uniform(25))
addAlien()
}
}
override func update(currentTime: CFTimeInterval) {
var timeSinceLastUpdate = currentTime - lastUpdateTimerInterval
lastUpdateTimerInterval = currentTime
if score < 60{
velocity = CGFloat(score*3)
}else{
velocity = CGFloat(210)
}
if (timeSinceLastUpdate > 1){
timeSinceLastUpdate = 1/60
lastUpdateTimerInterval = currentTime
}
updateWithTimeSinceLastUpdate(timeSinceLastUpdate)
}
override func touchesBegan(touches: NSSet, withEvent event: UIEvent) {
/* Called when a touch begins */
for touch: AnyObject in touches {
let location = touch.locationInNode(self)
if self.nodeAtPoint(location) == self.alien{
alien.removeFromParent()
score++
}
}
}
}

Answer 1

Everytime you add an alien you remove the last alien with this line of code:
alien.removeFromParent()
You have to create a new variable node in the addAlien() function and give the node a name
for example:
var alien:SKSpriteNode = SKSpriteNode(imageNamed: "alien")
alien.name = "alien"
Then you can remove the alien in the touchesBegan function by checking the node name
let node = self.nodeAtPoint(location)
if (node.name == "alien") {
}
And for the gravity you should move self.physicsWorld.gravity = CGVectorMake(0, -velocity) to the didMoveToView() function and change the last parameter to a constant