使用Firebase，我想异步获取数据并在TableView上显示，但是某些数据在TableView上重复

Question

使用Firebase，我想异步获取数据，然后在TableView上显示它，但是某些数据在TableView上重复。我认为这是因为我在For语句中使用了闭包，但是我不确定应该在何处调用它。

我试图在Dispatchqueue.main.async中调用setDataToArray，但是它不起作用。

Class PostTableViewController: UITableViewController {

    let db = Firestore.firestore()

    var postArray: [Post] = [Post]()

    override func viewDidLoad() {
        super.viewDidLoad()

        SVProgressHUD.show()
        configureTableview()
        setDataToArray()
    }

    func setDataToArray() {

        retrievePost() { (posts) in

            print(posts!)

            for post in posts! {

                self.postArray.append(post)

            }

            print(self.postArray)
            self.tableView.reloadData()
            SVProgressHUD.dismiss()

        }
    }

    func retrievePost(completion: @escaping ([Post]?) -> Void) {

        var posts = [Post]()
        let postsColRef = db.collection("posts").order(by: "createdAt")

        postsColRef.getDocuments() { (querySnapshot, error) in
            if let error = error {
                print("Document data: \(error)")
            } else {
                for document in querySnapshot!.documents {
                    let data = document.data()
                    let userId = data["userId"] as? String
                    let postImage = data["postImageURL"] as? String
                    let postText = data["postText"] as? String
                    let createdAt = data["createdAt"] as? String
                    let numberOfLike = data["numberOfLike"] as? Int
                    let docRef = self.db.collection("users").document(userId!)

                    docRef.getDocument() { (document, error) in
                        if let document = document, document.exists {

                            let data = document.data()!
                            let userName = data["userName"] as? String
                            let userImage = data["userImageURL"] as? String

                            let post = Post(
                                userId: userId!,
                                userName: userName!,
                                userImageURL: userImage!,
                                postImageURL: postImage!,
                                postText: postText!,
                                createdAt: createdAt!,
                                numberOfLike: numberOfLike!)

                            print(post)
                            posts.append(post)
                            completion(posts)
                        }
                    }
                }
            }
        }
    }

    @IBAction func cameraButtonPressed(_ sender: UIBarButtonItem) {

        performSegue(withIdentifier: "homeToChooseImage", sender: nil)

    }



    }


    extension PostTableViewController {

    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {

        return postArray.count
    }

    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {

        let cell = tableView.dequeueReusableCell(withIdentifier: "postCell", for: indexPath) as! PostTableViewCell

        let post = postArray[indexPath.row]

        let postImageURL = URL(string: post.postImageURL)

        do {
            let data = try Data(contentsOf: postImageURL!)
            cell.postImage.image = UIImage(data: data)
        }catch let err {
            print("Error : \(err.localizedDescription)")
        }

        let userImageURL = URL(string: post.userImageURL)

        do {
            let data = try Data(contentsOf: userImageURL!)
            cell.userImage.image = UIImage(data: data)
        }catch let err {
            print("Error : \(err.localizedDescription)")
        }

        cell.postText.text = post.postText

        cell.userName.text = post.userName

        cell.createdAt.text = post.createdAt

        cell.postLikeButton.titleLabel?.text = "\(post.numberOfLike) Likes"

        return cell
    }

}

我猜我在哪里称“完成（帖子）”是错误的。 我应该在哪里称呼它呢？