这让我抓狂。只有在第一次运行时，viewDidLayoutSubviews才被调用两次。
下面是我使用的代码：

class CICViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    func addQLabel(qLabel: UILabel, questionString: String, bgrLabel: UILabel) {// some code goes here
    }

    func makeRoundQButtons(qButtons:[UIButton]) {
      // some code goes here

    }

    func addArrows(numberOfArrows:Int, buttonCurAngle:Double) {//some code goes here
    }

    func animateButtons(qButtons:[UIButton], buttonCurAngle:Double) {

     // some code goes here

    }

    override func viewDidAppear(animated: Bool) {
        super.viewDidAppear(animated)

    }

    func backTapped(sender: UIBarButtonItem) {
        navigationController?.popViewControllerAnimated(false)
       //some code goes here

    }

    func restartTapped(sender: UIBarButtonItem) {
        navigationController?.popToRootViewControllerAnimated(false)
        //some code goes here
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }

}

在我的ViewController中，我称之为：

class OneViewController: CICViewController {

  override func viewDidLoad() {
        super.viewDidLoad()

 //some code goes here
}

    override func viewDidLayoutSubviews() {

        super.viewDidLayoutSubviews()
        print("viewDidLayoutSubviews")
        self.makeRoundQButtons(qButtons)
        self.animateButtons(qButtons, buttonCurAngle: 2.0)

    }

    override func viewDidAppear(animated: Bool) {
     //nothing goes here
    }

}