在使用Swift的SpriteKit中，如何设置子节点数量的特定限制？

Question

I have a simple scene which adds a bouncing ball to the scene once a user touches in an area. The goal will be to bounce the balls off pins in order to 'score' in a certain area.

I'm just at the very beginning of coding the app, but I can't as yet find a way to create a limit for the amount of balls a user can generate. At the moment, they can generate any number of balls and over-saturate the scene, leading to a drop in FPS and a very easy game!

override func touchesBegan(touches: NSSet, withEvent event: UIEvent) {
    /* Called when a touch begins */

    for touch: AnyObject in touches {
        let location = touch.locationInNode(self)

        let ball = SKSpriteNode(imageNamed:"ball")

        ball.xScale = 0.2
        ball.yScale = 0.2
        ball.position = location

        ball.physicsBody = SKPhysicsBody(circleOfRadius: ball.size.height / 2.0)
        ball.physicsBody!.dynamic = true

        ball.physicsBody!.friction = 0
        ball.physicsBody!.restitution = 0.8

        ball.name = "ball"

        self.addChild(ball)

    }
}

override func update(currentTime: CFTimeInterval) {
    /* Called before each frame is rendered */

}

I know I need to ask the scene how many ball nodes are in the scene and then remove a ball once it reached a limit but everything I seem to try results in errors.

Answer 1

there are a ton of ways to do this, but this is probably the easiest. NOTE: unless you remove balls from the scene at some point, you're going to hit a ten ball limit and get stuck.

override func touchesBegan(touches: NSSet, withEvent event: UIEvent) {
    /* Called when a touch begins */

    for touch: AnyObject in touches {
        let location = touch.locationInNode(self)

        // ball limit
        let limit = 10

        // setup counter
        var i = 0

        // loop through the ball nodes added to the scene
        self.enumerateChildNodesWithName("ball", usingBlock: {
            _, _ in  // we dont need to use these variables right now   
            i += 1  // increment the counter
        })

        // if we haven't hit our limit, add a ball (YOUR CODE HERE)
        if i <= limit {

            let ball = SKSpriteNode(imageNamed:"ball")

            ball.xScale = 0.2
            ball.yScale = 0.2
            ball.position = location

            ball.physicsBody = SKPhysicsBody(circleOfRadius: ball.size.height / 2.0)
            ball.physicsBody!.dynamic = true

            ball.physicsBody!.friction = 0
            ball.physicsBody!.restitution = 0.8

            ball.name = "ball"

            self.addChild(ball)

        }

    }
}