问iOS 11 SpriteKit游戏的速度不会超过每秒30帧

EN

    func getCollectable() -> SKSpriteNode {

    var collecatble = SKSpriteNode()

    if Int(randomBetweenNumbers(firstNum: 0, secondNum: 9)) == 4 {
        //Come Back
        if GamePlayController.instance.life! < 100 {
            collecatble = SKSpriteNode(imageNamed: "MonsterRobot")
            collecatble.name = "Monster"
            collecatble.physicsBody = SKPhysicsBody(rectangleOf: collecatble.size)
            collecatble.yScale = 0.09
            collecatble.xScale = 0.09

        }else{
            collecatble.name = "Empty"
        }
    }else{

        collecatble = SKSpriteNode(imageNamed: "Coin2")
        collecatble.name = "Coin2"
        collecatble.physicsBody = SKPhysicsBody(rectangleOf: collecatble.size)

    }
    if Int(randomBetweenNumbers(firstNum: 0, secondNum: 100)) == 51 {

        collecatble = SKSpriteNode(imageNamed: "Slow icon")
        collecatble.name = "SlowIcon"
        collecatble.physicsBody = SKPhysicsBody(rectangleOf: collecatble.size)
        collecatble.yScale = 0.05
        collecatble.xScale = 0.05
    }

    collecatble.physicsBody?.affectedByGravity = false
    collecatble.physicsBody?.categoryBitMask = ColliderType.DarkCloudAndCollectables
    collecatble.physicsBody?.collisionBitMask = ColliderType.Player
    collecatble.zPosition = 2


    return collecatble

}



 func randomBetweenNumbers(firstNum: CGFloat, secondNum: CGFloat) -> CGFloat {

    return CGFloat(arc4random()) / CGFloat(UINT32_MAX) * abs(firstNum - secondNum) + min(firstNum, secondNum)
}