为什么我在使用该值时得到一个 nil 值，但当我打印它时它显示为 none nil？

Question

我正在尝试填充集合视图。当我在字典中使用一个值时，它显示为 nil，但是当我打印它时，它会在它为我提供字符串之前的行。

我之前修复了这个问题，但是当我重新制作我的收藏视图以解决我遇到的另一个错误时，这个错误又回来了。为了解决这个问题，我刚刚删除了 self.users.removeAll() 行。重新添加该行然后删除它这次不起作用。

我在这个函数中遇到了问题：

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {

    let cell = collectionview.dequeueReusableCell(withReuseIdentifier: "userCell", for: indexPath) as! UserCell

    print(user[indexPath.row].imagePath!)

    cell.userImage.sd_setImage(with: URL(string: user[indexPath.row].imagePath!))

    cell.nameLabel.text = user[indexPath.row].username
    cell.userID = user[indexPath.row].userID

    return cell
}

这里是完整的代码：

import UIKit
import Firebase
import SwiftKeychainWrapper
import SwiftUI
import FirebaseUI

class UserViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource {

    @IBOutlet weak var collectionview: UICollectionView!

    var user = [User]()

    override func viewDidLoad() {
        super.viewDidLoad()
        collectionview.delegate = self
        collectionview.dataSource = self

        retrieveUsers()
    }

    func retrieveUsers() {
       let ref = Database.database().reference()
       ref.child("users/").observeSingleEvent(of:.value, with: { (snapshot) in
          let users = snapshot.value as! [String : NSDictionary]
          //self.user.removeAll()
          for (_, value) in users {
             if let uid = value["uid"] as? String {
                if uid != Auth.auth().currentUser!.uid {
                   let userToShow = User()
                   if let username = value["username"] as? String, let imagePath = value["urlToImage"] as? String {
                      userToShow.username = username
                      userToShow.imagePath = imagePath
                      userToShow.userID = uid
                      self.user.append(userToShow)
                      print(userToShow)
                   }
                }
             }
          }

          self.collectionview.reloadData()
       })

       ref.removeAllObservers()
    }

    func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionview.dequeueReusableCell(withReuseIdentifier: "userCell", for: indexPath) as! UserCell

        print(user[indexPath.row].imagePath!)

        cell.userImage.sd_setImage(with: URL(string: user[indexPath.row].imagePath!))
        cell.nameLabel.text = user[indexPath.row].username
        cell.userID = user[indexPath.row].userID

        return cell
    }

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return user.count //?? 0
    }

    func checkFollowing(indexPath: IndexPath) {
       let uid = Auth.auth().currentUser!.uid
       let ref = Database.database().reference()

       ref.child("users").child(uid).child("following").queryOrderedByKey().observeSingleEvent(of: .value, with: { snapshot in
           if let following = snapshot.value as? [String : AnyObject] {
              for (_, value) in following {
                 if value as! String == self.user[indexPath.row].userID {
//                  self.tableview.cellForRow(at: indexPath)?.accessoryType = .checkmark
                 }
              }
           }
       })

       ref.removeAllObservers()

    }

    @IBAction func logOutPressed(_ sender: Any) {
        KeychainWrapper.standard.removeObject(forKey:"uid")

        do {
            try Auth.auth().signOut()
        } catch let signOutError as NSError{
            print("Error signing out: %@", signOutError)
        }
        dismiss(animated: true, completion: nil)
    }
}


extension UIImageView {
    func downloadImage(from imgURL: String!) {
        let url = URLRequest(url: URL(string: imgURL)!)

        let task = URLSession.shared.dataTask(with: url) {  (data, response, error) in
            if error != nil {
                print(error!)
                return
            }

            DispatchQueue.main.async {
                self.image = UIImage(data: data!)
            }
        }

        task.resume()
    }
}

我没有正确填充字典吗？

另外，这里是 User 类：

import UIKit

class User: NSObject {
    var userID: String?
    var username: String?
    var imagePath: String?
}

另外，这是用户字典在调试器中显示的内容：

Answer 1

如果您遇到此错误，请重新连接到您的集合视图单元