发送到新ViewController的数据将以nil的形式发送

Question

当我尝试将Event类的详细信息传递给另一个控制器时，我收到一条错误消息“致命错误：在展开Optional值时意外发现nil”。

这是我的视图控制器，它发送信息：

var eventDetailsController: EventDetailsController!

func showDetailView(event: Events){
    let mainStoryBoarrd: UIStoryboard = UIStoryboard(name:"Main",     bundle:nil)
    let detailsViewController: UIViewController = mainStoryBoarrd.instantiateViewControllerWithIdentifier("eventDetailsID")

    print(event)      // this prints the event fine showing that the event variable is not nil
    eventDetailsController?.event = event //this sends all info as nil


    self.presentViewController(detailsViewController, animated: true, completion: nil)
}

这是我将数据发送到的类：

var event: Events!   {
    didSet  {
        eventPriceLabel.text = event!.date //does nothing cause nil
    }
}

override func viewDidLoad() {
    super.viewDidLoad()

    let string = event?.name
    print(string)// prints null
}

我的活动课程：

class Events: NSObject {
var name: String!
var date: String!
var address: String!
var ticketPrice: Int!