UIAlertController未显示第一次运行应用程序

Question

当收到推送通知且应用程序处于打开状态时，我会从AppDelegate显示UIAlertController。问题是，警报不会在第一次运行应用程序时显示。如果您在Xcode中停止应用程序然后重新启动它，一切都按预期工作。

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterDelegate {

   var alert: UIAlertController?

   func userNotificationCenter(_ center: UNUserNotificationCenter,  willPresent notification: UNNotification, withCompletionHandler   completionHandler: @escaping (_ options:   UNNotificationPresentationOptions) -> Void) {
      self.showAlert(title: title,message:body,buttonTitle:"View",window:self.window!)
   }

   func showAlert(title: String,message : String,buttonTitle: String,window: UIWindow){
      self.alert = UIAlertController(title: title, message: message, preferredStyle: UIAlertControllerStyle.alert)
      alert?.addAction(UIAlertAction(title: buttonTitle, style: UIAlertActionStyle.default, handler: { (action) in

      //self.messageDelegate?.goToMessages()
   }))

   alert?.addAction(UIAlertAction(title: "Cancel", style: UIAlertActionStyle.default, handler: nil))

   window.rootViewController?.present(alert!, animated: false, completion: nil)
   }
}