reloadData() for collection View 不起作用

Question

我在重新加载collectionview时遇到问题。当我removeAll()然后fetchPosts()时，它只会创建重复项，而不会删除我认为(暂时(已删除的帖子。我使用 removeAll() 和 fetchPosts() 的原因是因为我有 Firebase 后端，它会获取帖子，但在发布图片后不会更新。当我尝试self.collectionview.reloadData()时，它不会显示新帖子。提前感谢！

这是我的代码：

@IBOutlet weak var collectionview: UICollectionView!
var posts = [Post]()
var following = [String]()
lazy var refreshControl: UIRefreshControl? = {
    let refreshControl = UIRefreshControl()
    refreshControl.tintColor = UIColor.gray
    refreshControl.addTarget(self, action: #selector(refreshList), for: UIControlEvents.valueChanged)
    collectionview.addSubview(refreshControl)
    return refreshControl
}()
override func viewDidLoad() {
    super.viewDidLoad()
    setupNavigationBarItems()
    fetchPosts()
    collectionview.refreshControl = refreshControl
}
func setupNavigationBarItems() {
    navigationItem.title = "Home"
}
@objc func refreshList() {
    let deadline = DispatchTime.now() + .milliseconds(1000)
    DispatchQueue.main.asyncAfter(deadline: deadline) {
        self.self.posts.removeAll()
        self.fetchPosts()
        self.collectionview.reloadData()
        print("reloading")
        self.refreshControl?.endRefreshing()
    }
}
@objc func fetchPosts() {
    let ref = Database.database().reference()
    ref.child("users").queryOrderedByKey().observeSingleEvent(of: .value, with: { snapshot in
        let users = snapshot.value as! [String : AnyObject]
        for (_,value) in users {
            if let uid = value["uid"] as? String {
                if uid == Auth.auth().currentUser?.uid {
                    if let followingUsers = value["following"] as? [String : String]{
                        for (_,user) in followingUsers{
                            self.following.append(user)
                        }
                    }
                    self.following.append(Auth.auth().currentUser!.uid)
                    ref.child("posts").queryOrderedByKey().observeSingleEvent(of: .value, with: { (snap) in

                        let postsSnap = snap.value as! [String : AnyObject]
                        for (_,post) in postsSnap {
                            if let userID = post["userID"] as? String {
                                for each in self.following {
                                    if each == userID {
                                        let posst = Post()
                                        if let author = post["author"] as? String, let likes = post["likes"] as? Int, let pathToImage = post["pathToImage"] as? String, let postID = post["postID"] as? String {
                                            posst.author = author
                                            posst.likes = likes
                                            posst.pathToImage = pathToImage
                                            posst.postID = postID
                                            posst.userID = userID
                                            if let people = post["peopleWhoLike"] as? [String : AnyObject] {
                                                for (_,person) in people {
                                                    posst.peopleWhoLike.append(person as! String)
                                                }
                                            }
                                            self.posts.append(posst)
                                        }
                                    }
                                }
                                self.collectionview.reloadData()
                            }
                        }
                    })
                }
            }
        }
    })
    ref.removeAllObservers()
}
func numberOfSections(in collectionView: UICollectionView) -> Int {
    return 1
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return self.posts.count
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "postCell", for: indexPath) as! PostCell
    cell.postImage.downloadImage(from: self.posts[indexPath.row].pathToImage)
    cell.authorLabel.text = self.posts[indexPath.row].author
    cell.likeLabel.text = "(self.posts[indexPath.row].likes!) Likes"
    cell.postID = self.posts[indexPath.row].postID

    for person in self.posts[indexPath.row].peopleWhoLike {
        if person == Auth.auth().currentUser!.uid {
            cell.likeBtn.isHidden = true
            cell.dislikeBtn.isHidden = false
            break
        }
    }
    return cell
}

}

Answer 1

in FetchPost 函数

@objc func fetchPosts() {
     self.posts.removeAll()

}