如何设置导航项目的标题？

Question

我试图设置导航项目的标题。

但我收到如下错误消息

有人知道这个问题吗？

这是我的代码

导入UIKit

import Parse

var show = String()
var user = String()


class FansTableVC: UITableViewController {

    //Arrays to hold data received from servers
    var usernameArray = [String]()
    var profileImgArray = [PFFile]()

    // Array showing who do we follow or who followings us
    var myfansArray = [String]()

    //Array showing who do we follow or who following us
    var followingArray = [String]()


    override func viewDidLoad() {
        super.viewDidLoad()

        //Title at the top
        self.navigationItem.title = show

        // New back button
        self.navigationItem.hidesBackButton = true
        let backButton = UIBarButtonItem(image: UIImage(named: "backBtn"), style: UIBarButtonItemStyle.plain, target: self, action: #selector(FansTableVC.back(_:)))

        self.navigationItem.leftBarButtonItem = backButton
        self.navigationItem.leftBarButtonItem?.setBackgroundVerticalPositionAdjustment(-8, for: UIBarMetrics.default)

//        self.edgesForExtendedLayout=UIRectEdge.None;
//        self.extendedLayoutIncludesOpaqueBars = false;
//        self.automaticallyAdjustsScrollViewInsets = false


//        self.tableView.contentOffset = CGPointMake(0, 44.0);
        self.tableView.contentInset = UIEdgeInsetsMake(16.0, 0.0, 0.0, 0.0);


        self.tableView!.rowHeight = UITableViewAutomaticDimension;
        self.tableView!.estimatedRowHeight = 82.0 //needed for autolayout




        //load Fans
        if show == "Fans" {
            loadFans()
        }

        //load Followings
        if show == "Followings" {
            loadFollowings()
        }


    }
    //cell height
    override func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
        return UITableViewAutomaticDimension
    }

此代码在Xcode 7中运行良好。它刚刚发生在Xcode 8