Question

当我尝试将Event类的详细信息传递给另一个控制器时，我收到错误消息"fatal error: unexpectedly found nil while unwrapping an Optional value"。

这是我的视图控制器，它发送信息：

var eventDetailscontrollers: EventDetailsController!

func showDetailView(event: Events){
    let mainStoryBoarrd: UIStoryboard = UIStoryboard(name:"Main", bundle:nil)
    let detailsViewController: UIViewController = mainStoryBoarrd.instantiateViewControllerWithIdentifier("eventDetailsID")
    eventDetailscontrollers?.event = event //this sends all info as nil
    eventDetailscontrollers.event = event //this causes error

    print(event.name)      // this prints event name fine

    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
    }
}

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!

Answer 1

您的问题是您要声明变量eventDetailscontrollers，如下所示：

var eventDetailscontrollers: EventDetailsController!

但你永远不会给它分配一个值，所以如果你打电话

就是这个原因

eventDetailscontrollers.event

这会因eventDetailscontrollers为nil而崩溃，因此当时没有成员event。

但是当你打电话时

eventDetailscontrollers?.event

这不会崩溃，因为只有当event不是eventDetailscontrollers时，才会为nil成员分配值，这就是感叹号的含义。 eventDetailscontrollers实际上是nil，因此不会进行任务分配。

因此，您需要先初始化eventDetailscontrollers变量。

我建议你阅读本指南关于optionals，以及关于optional chaining的这个指南

Answer 2

问题在于：

func showDetailView(event: Events){
    let mainStoryBoarrd: UIStoryboard = UIStoryboard(name:"Main", bundle:nil)
    let detailsViewController: UIViewController = mainStoryBoarrd.instantiateViewControllerWithIdentifier("eventDetailsID")
    eventDetailscontrollers?.event = event //this sends all info as nil
    eventDetailscontrollers.event = event //this causes error

    print(event.name)      // this prints event name fine

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

您有两个应该相同的变量：

func showDetailView(event: Events){
    let mainStoryBoarrd: UIStoryboard = UIStoryboard(name:"Main", bundle:nil)
    eventDetailscontrollers = mainStoryBoarrd.instantiateViewControllerWithIdentifier("eventDetailsID")
    eventDetailscontrollers?.event = event //this sends all info as nil
    eventDetailscontrollers.event = event //this causes error

    print(event.name)      // this prints event name fine

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

发送到新View Controller的数据为nil，展开可选值

2 个答案: