class ViewController: UIViewController {

    var delegate : AppDelegate
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view,typically from a nib.
        //self.appDelegate = UIApplication.sharedApplication().delegate;

    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    @IBAction func getData(sender : AnyObject) {

    }

    @IBAction func logout(sender : AnyObject) {
    }
}

但是，如果我只是添加？在AppDelegate的结尾，如下所示，错误消失了。

class ViewController: UIViewController {

    var delegate : AppDelegate?
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view,typically from a nib.
        //self.appDelegate = UIApplication.sharedApplication().delegate;

    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    @IBAction func getData(sender : AnyObject) {

    }

    @IBAction func logout(sender : AnyObject) {
    }
}

我没有看到可选关键字与此错误相关，除非我错了。
有什么想法。随意评论。欣赏它。

谢谢