UI导航栏在按后退按钮时消失

Question

[您可以在表格视图中搜索用户，它在UInavigation控制器中显示后退按钮（如图）。当我点击一行时，它会将我带到表格视图的个人资料页面-但是，当我从表格视图中单击返回时，顶部的按钮和UI导航控制器消失，您只能通过滑动来返回。我不确定为什么会这样。

Tableview的导航控制器嵌入到容纳UIView控制器的页面视图控制器中。

代码1显示了表格视图代码2显示了个人资料页面。非常感谢任何帮助。

import UIKit
import FirebaseFirestore
import Firebase

class ListOfUsersFromUniversity: UIViewController, UISearchBarDelegate {

    
    @IBOutlet weak var searchBar: UISearchBar!
    
    @IBOutlet weak var tableView: UITableView!
    
    
    var University:String = ""
    var users = [String]()
    var filteredUsers = [String]()
    var searching = false
          
  override func viewDidLoad() {
      super.viewDidLoad()
      tableView.delegate = self
      tableView.dataSource = self
      searchBar.delegate = self
      tableView.reloadData()
          }
         

              
    func searchBarTextDidBeginEditing(_ searchBar: UISearchBar) {
        searchBar.becomeFirstResponder()
    }
    
      func searchBar(_ searchBar: UISearchBar, textDidChange searchText: String) {
          filteredUsers = users.filter({$0.lowercased().prefix(searchText.count) == searchText.lowercased()})
          searching = true
          tableView.reloadData()
      }
          
    
    override func viewWillAppear(_ animated: Bool) {
       self.navigationController?.navigationBar.isHidden = false
        let docRef = Firestore.firestore().collection("User-Universities").document(University)
        docRef.getDocument{ (document, error) in
          if let document = document {
          let data = document.data()
           let keydict = data!.keys
           let stringArray = Array(keydict)
           print(stringArray)
           for user in stringArray {
               service.getUsernameFromUID(user) { (username) in
                   self.users.append(username)
               }
           }
          } else {
            print("Document does not exist")
          }
        }
        DispatchQueue.main.async {
            self.tableView.reloadData()
        }
        
        searchBar.becomeFirstResponder()
    }
    
    
    override func viewWillDisappear(_ animated: Bool) {
        users.removeAll()
    }
        }
          


extension ListOfUsersFromUniversity: UITableViewDelegate, UITableViewDataSource  {
    
    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
            if searching {
                return filteredUsers.count
                } else {
                return users.count
                }
            }
        
        
        func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
            let cell = tableView.dequeueReusableCell(withIdentifier: "cell")!
            if searching {
                cell.textLabel?.text = filteredUsers[indexPath.row]
            } else {
                cell.textLabel?.text = users[indexPath.row]
            }
            return cell
            
        }
        
        func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
            let cell = tableView.cellForRow(at: indexPath)!
            let username = cell.textLabel!.text ?? ""
            let storyboard = UIStoryboard(name: "Search", bundle: nil)
      
            let newVC = storyboard.instantiateViewController(withIdentifier: "ProfilePage") as! ProfileViewController
            newVC.username = username
           // let navigationController = UINavigationController()
            self.navigationController?.pushViewController(newVC, animated: true)
            
            }
            

    }

import UIKit
import FirebaseFirestore
import Firebase
import Kingfisher

class ProfileViewController: UIViewController {

    let docRef = Firestore.firestore().collection("users")
    var username:String = ""
    
    override func viewDidLoad() {
        super.viewDidLoad()
        navigationController?.navigationBar.prefersLargeTitles = true
        self.title = username

        // Do any additional setup after loading the view.
    }
    
    override func viewWillAppear(_ animated: Bool) {
    self.navigationController?.navigationBar.isHidden = false
    }
    
}

extension ProfileViewController: UICollectionViewDataSource{
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 12
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "PostProfileCell", for: indexPath) as! PostCollectionCell
        cell.backgroundColor = .red
        return cell
    }
    
    func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {
        guard kind == UICollectionView.elementKindSectionHeader else {
        fatalError("Unexpected element kind.")
    }
    
        let headerView = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: "ProfileHeader", for: indexPath) as! UserProfileHeaderCell
        
        docRef.whereField("username", isEqualTo: username)
            .getDocuments() { (querySnapshot, err) in
                if let err = err {
                    print("Error getting documents: \(err)")
                } else {
                    for document in querySnapshot!.documents {
                      let data = document.data()
                        let Link = data["ProfilePicUrl"] as? String ?? ""
                        let username = data["username"] as? String ?? ""
                        let university = data["University"] as? String ?? ""
                        let course = data["Course"] as? String ?? ""
                        let friends = data["friends"] as? Int
                        let url = URL(string: Link)
            DispatchQueue.main.async {
                headerView.University.text = university
                headerView.Course.text = course
                headerView.Friends.text = String(describing: friends!)
                headerView.profilePicture.layer.cornerRadius = headerView.profilePicture.frame.size.width/2
                headerView.profilePicture.clipsToBounds = true
                let placeholder = UIImage(systemName: "person.circle")
                headerView.profilePicture.kf.setImage(with: url, placeholder: placeholder)
                    }
                }
            }
        }
        
        
    return headerView
    }
    
    override func viewWillDisappear(_ animated: Bool) {
    self.navigationController?.navigationBar.isHidden = true
    }
    
}

extension ProfileViewController: UICollectionViewDelegateFlowLayout{
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        let columns: CGFloat = 3
         let spacing: CGFloat = 1.5
         let totalHorizontalSpacing = (columns - 1) * spacing

         let itemWidth = (collectionView.bounds.width - totalHorizontalSpacing) / columns
         let itemSize = CGSize(width: itemWidth, height: itemWidth)

        return itemSize
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumInteritemSpacingForSectionAt section: Int) -> CGFloat {
        return 1.5
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat {
        return 1.5
    }
}

Answer 1

您可以使用viewWillAppear将其设置为可见。

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    navigationController?.setNavigationBarHidden(false, animated: true)
}