我正在使用MessageKit。我创建了一个MessageViewController。我添加了messageInputBar作为viewDidLoad的子视图，沿着一个包含后退按钮的导航栏。每当我在这个视图控制器中点击messageInputBar的文本字段，然后点击后退按钮时，当应用程序返回到上一个UIViewController时，messageInputBar将保留在屏幕上。如果我不“当我第一次进入MessagesViewController并按下back按钮时，如果不点击messageInputBar，则messageInputBar会被正确地关闭。

override func viewDidLoad() {
        super.viewDidLoad()

        setUpNavBar()

        navigationItem.largeTitleDisplayMode = .never
        maintainPositionOnKeyboardFrameChanged = true
        scrollsToLastItemOnKeyboardBeginsEditing = true

        messageInputBar.inputTextView.tintColor = .systemBlue
        messageInputBar.sendButton.setTitleColor(.systemTeal, for: .normal)

        messageInputBar.delegate = self
        messagesCollectionView.messagesDataSource = self
        messagesCollectionView.messagesLayoutDelegate = self
        messagesCollectionView.messagesDisplayDelegate = self

        loadChat()

        self.view.addSubview(messageInputBar)

        messageInputBar.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            messageInputBar.bottomAnchor.constraint(equalTo: self.view.bottomAnchor),
            messageInputBar.widthAnchor.constraint(equalToConstant: self.view.bounds.width)
        ])

        NSLayoutConstraint.activate([
            messagesCollectionView.topAnchor.constraint(equalTo: self.view.topAnchor, constant: 100)
        ])

    }

    func setUpNavBar() {
        let navBar = UINavigationBar()
        self.view.addSubview(navBar)
        navBar.items?.append(UINavigationItem(title: (selectedUser?.userFirstName)!))
        let backButton = UIBarButtonItem(title: "Back", style: .plain, target: self, action: #selector(backButtonTapped))
        navBar.topItem?.leftBarButtonItem = backButton

        navBar.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            navBar.topAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.topAnchor),
            navBar.heightAnchor.constraint(equalToConstant: 44),
            navBar.widthAnchor.constraint(equalToConstant: self.view.bounds.width)
        ])
    }

    @IBAction func backButtonTapped(_ sender: Any) {
        let transition = CATransition()
        self.view.window!.layer.add(transition.segueLeftToRight(), forKey: kCATransition)

        self.dismiss(animated: false)
    }