用App更新视图控制器变量

Question

因此，我基本上是试图显示在应用程序中收到的推送通知。当收到通知时，我试图更新视图控制器的文本。但是，每次我试图更新视图控制器时，都会得到一个错误：fatal error: unexpectedly found nil while unwrapping an Optional value

以下是我的应用程序委托代码片段：

func application(application: UIApplication, didReceiveRemoteNotification userInfo: [NSObject : AnyObject],
                 fetchCompletionHandler completionHandler: (UIBackgroundFetchResult) -> Void) {
    // If you are receiving a notification message while your app is in the background,
    // this callback will not be fired till the user taps on the notification launching the application.
    // TODO: Handle data of notification

    // Print message ID.

    print("Message ID: \(userInfo["gcm.message_id"]!)")



    let vc = FirstViewController()


    vc.notificationText = "Test"
    print (vc.notificationText)
    vc.updateText()

    // Print full message.
    print("%@", userInfo)
}

以下是我的视图控制器：

class FirstViewController: UIViewController {


@IBOutlet weak var notificationLabel: UILabel!
var notificationText = "No notifications"

@IBAction func logOut(sender: AnyObject) {
    try! FIRAuth.auth()!.signOut()
    LogOutComplete()
}

func LogOutComplete() {
    let mainStoryboard = UIStoryboard(name: "Main", bundle: NSBundle.mainBundle())
    let logIn : UIViewController = mainStoryboard.instantiateViewControllerWithIdentifier("LogIn") as UIViewController
    self.presentViewController(logIn, animated: true, completion: nil)
}
override func viewDidLoad() {
    super.viewDidLoad()

    notificationLabel.text = notificationText

    //notificationLabel.text = notificationText
    // Do any additional setup after loading the view.
}

/*override func viewWillAppear(animated: Bool) {
    notificationLabel.text = notificationText
}*/

func updateText () {
    notificationLabel.text = notificationText
}

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

我真的不知道它为什么会给我这个错误。也许有人能解释并帮助我解决这个问题。感谢所有的帮助！

Answer 1

编辑的SWIFT2.2：

您正在application: didReceiveRemoteNotification方法中创建一个新的application: didReceiveRemoteNotification实例。因此，您正在更新与您想要更新的不同FirstViewController实例的属性。您正在更新的那个没有显示。错误的出现是因为updateText()正在被调用，但是故事板没有初始化，所以notificationLabel仍然是零。

若要执行您正在尝试的操作，请使用通知post将通知传递给视图控制器，并将FirstViewController添加为观察者：

在您的AppDelegate中，将主体更改为：

func application(application: UIApplication, didReceiveRemoteNotification userInfo: [NSObject : AnyObject],
             fetchCompletionHandler completionHandler: (UIBackgroundFetchResult) -> Void) {
// If you are receiving a notification message while your app is in the background,
// this callback will not be fired till the user taps on the notification launching the application.
// TODO: Handle data of notification

// Print message ID.

print("Message ID: \(userInfo["gcm.message_id"]!)")
NotificationCenter.default.post(name: "Add_Notification_Post_Name_Here", object: nil,
                                                              userInfo: userInfo)

}

在FirstViewController中，添加一个观察者来侦听通知帖子：

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    NotificationCenter.default.addObserver(self, selector: Some_Method_Name:, name: "Add_Notification_Post_Name_Here", object: nil)
}

在FirstViewController中，添加一个处理通知帖子的方法：

func Some_Method_Name(_ notification: NSNotification) {

guard let userInfo = notification.userInfo else {
        return
    }
    guard let payload = userInfo["Some_Message_Key_Here"] as? NSString  else {
        return
    }
    notificationText = String(payload)
    updateText()
}

此方法将包转换为要分配给通知文本的字符串类型的有效负载。然后调用updateText()函数。