iOS无法识别每次触摸

Question

我试图在用户点击屏幕时在屏幕上显示精灵。我正在使用Xcode提供的默认SpriteKit游戏，下面是我用来检测用户点击屏幕的方法。我遇到的问题是我经常点击屏幕，但精灵没有出现。任何想法为什么会这样？

override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
   /* Called when a touch begins */

    for touch in touches {

        let sprite = SKSpriteNode(imageNamed:"mySprite")

        sprite.xScale = 0.3
        sprite.yScale = 0.3

        let dotX = (drand48() * Double (view!.scene!.frame.size.width))
        let dotY = (drand48() * Double (view!.scene!.frame.size.height))

        print (dotX)
        print (dotY)

        sprite.position.x = CGFloat (dotX)
        sprite.position.y = CGFloat (dotY)

        self.addChild(sprite)

    }
}