Spawn enemies randomly only within the screen width - sprite-kit

Question

I started working with SKS files to create games in swift, and in this game im trying to get enemies to spawn randomly within the width of the phone screen as opposed to all over the sks file scene
override func didMoveToView(view: SKView) {
self.physicsWorld.contactDelegate = self
NSTimer.scheduledTimerWithTimeInterval(0.2, target: self, selector: Selector("spawnEnemy"), userInfo: nil, repeats: true)
}
func spawnEnemy(){
//supposed to pick random point within the screen width
let xPos = Int.random(self.frame.width)
enemy = SKSpriteNode(imageNamed: "enemy")
enemy.position = CGPointMake(CGFloat(xpos), self.frame.size.height/2)
enemy.physicsBody = SKPhysicsBody(circleOfRadius: 7)
enemy.physicsBody?.affectedByGravity = true
enemy.physicsBody?.categoryBitMask = 0
enemy.physicsBody?.contactTestBitMask = 1
addChild(self.enemy)
}

Answer 1

Anyways, I wrote an example for you :)
So, here is how your example should look in order to work:
override func didMoveToView(view: SKView) {
self.physicsWorld.contactDelegate = self
NSTimer.scheduledTimerWithTimeInterval(0.2, target: self, selector: Selector("spawnEnemy"), userInfo: nil, repeats: true)
}
func randomBetweenNumbers(firstNum: CGFloat, secondNum: CGFloat) -> CGFloat{
return CGFloat(arc4random()) / CGFloat(UINT32_MAX) * abs(firstNum - secondNum) + min(firstNum, secondNum)
}
func spawnEnemy(){
//supposed to pick random point within the screen width
let xPos = randomBetweenNumbers(0, secondNum: frame.width )
let enemy = SKSpriteNode(imageNamed: "enemy") //create a new enemy each time
enemy.position = CGPointMake(CGFloat(xPos), self.frame.size.height/2)
enemy.physicsBody = SKPhysicsBody(circleOfRadius: 7)
enemy.physicsBody?.affectedByGravity = true
enemy.physicsBody?.categoryBitMask = 0
enemy.physicsBody?.contactTestBitMask = 1
addChild(enemy)
}
Method randomBetweenNumbers is borrowed from here.
And, this is another way of how you can spawn enemies by using SKAction:
override func didMoveToView(view: SKView) {
self.physicsWorld.contactDelegate = self
let wait = SKAction .waitForDuration(1, withRange: 0.5)
let spawn = SKAction.runBlock({
self.spawnEnemy()
})
let spawning = SKAction.sequence([wait,spawn])
self.runAction(SKAction.repeatActionForever(spawning), withKey:"spawning")
}
Method spawnEnemy remains the same in both cases. To stop spawning you can remove an action for certain key ("spawning" in this case). You can do it like this:
if((self.actionForKey("spawning")) != nil){
self.removeActionForKey("spawning")
}