如何查找使用扩展viewcontroller类的viewcontroller

override func viewDidAppear(_ animated: Bool) {
    //registering gcm reciever
    NotificationCenter.default.addObserver(self,
                                           selector: #selector(showReceivedGCMMessageCore(_:)),
                                           name: NSNotification.Name(rawValue: appDelegate.messageKey), object: nil)
}
override func viewDidDisappear(_ animated: Bool) {
     NotificationCenter.default.removeObserver(self, name: NSNotification.Name(rawValue: appDelegate.messageKey), object: nil)
}

我的扩展Corecontroller类viewdidAppear和ViewDidInviser在上面我管理了notification observer和removeobserver。 在此之后,我需要扩展的corecontroller类和继承的corecontroller类

//在我的viewcontroller中

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
}
override func viewDidDisappear(_ animated: Bool) {
    super.viewDidDisappear(animated)
}   

但我缺少的是一个viewcontroller在消失时没有移除观测者(由于这一功能,即播放声音就是在后台说话),我只想知道哪个viewcontroller正在接收FCM。(在其中接收FCM消息的viewcontroller类)