问我正在以编程方式设置viewController的视图，但在单击按钮后，viewController将不会出现？

EN

import Foundation
import Firebase

class NewDMViewController: UITableViewController, UITextViewDelegate {

    override func viewDidLoad() {
        super.viewDidLoad()
        tableView.delegate = self


        let image = UIImage(named: "new_message_icon")
        navigationItem.rightBarButtonItem = UIBarButtonItem(image: image, style: .plain, target: self, action: #selector(handleNewMessage))

        navigationItem.leftBarButtonItem = UIBarButtonItem( title: "Back", style: .plain, target: self, action: #selector(backButton))
        checkLogin()
    }
    @objc func handleNewMessage() {
        let newMessageViewController = NewMessageViewController()
        let navController = UINavigationController(rootViewController: newMessageViewController)
        present(navController, animated: true, completion: nil)

    }

    func checkLogin() {
        if Auth.auth().currentUser?.uid == nil {
            perform(#selector(backButton), with:nil, afterDelay:0)
        } else {
            let uid = Auth.auth().currentUser?.uid
            Database.database().reference().child("users").child(uid!).observeSingleEvent(of: .value, with: {(snapshot)
                in
                if let dictionary = snapshot.value as? [String: AnyObject] {
                    self.navigationItem.title = dictionary["name"] as? String
                }

            }, withCancel: nil)
        }
    }
    @objc func backButton(){ // pushes to rommateviewController

    }
}