为什么不调用委托方法？

Question

我正在尝试通知 ChatViewController 使用协议在 MessagesViewController 中删除了聊天，但从未调用在 ChatViewController 中实现的委托方法。
在 navigationController 层次结构中，ChatViewController 位于 MessagesViewController 之上。

protocol MessagesViewControllerDelegate:class {
  func chatWasDeletedFromDatabase(chatUID: String)
}

class MessagesViewController: UITableViewController {
    weak var delegate: MessagesViewControllerDelegate?

  func observeChatRemoved() {
    print("it is gonna be called")
           //inform ChatViewController that a chat was deleted.
   self.delegate?.chatWasDeletedFromDatabase(chatUID: chat.chatUID)
    print("was called here") //prints as expected
  }
}


  class ChatViewController: JSQMessagesViewController {

     var messagesVC: MessagesViewController? 

    override func viewDidLoad() {
      super.viewDidLoad()

     messagesVC = storyboard?.instantiateViewController(withIdentifier: "MessagesViewController") as! MessagesViewController
     messagesVC?.delegate = self
   }
 }


    extension ChatViewController: MessagesViewControllerDelegate {
    func chatWasDeletedFromDatabase(chatUID: String) {
    print("chatWasDeletedFromDatabase called") //never prints out
      if self.chatSelected.chatUID == chatUID {
         //popToRootViewController
       }

 }

Answer 1

好像

weak var delegate: MessagesViewControllerDelegate?

是 nil 您必须将它设置为 ChatViewController 呈现的实例，无论您如何呈现它

let chat = ///
self.delegate = chat
self.navigationController?.pushViewController(chat,animated:true)

也做

chat.messagesVC = self

这样

 messagesVC = storyboard?.instantiateViewController(withIdentifier: "MessagesViewController") as! MessagesViewController
 messagesVC?.delegate = self

不是当前显示的 messagesVC ，所以注释上面两行

为什么不调用委托方法？

Why delegate method is not called?

swift

swift-protocols