Firebase queryOrderedByKey没有按时间顺序对帖子进行排序

Question

我的应用程序有一个集合视图，显示来自Firebase的照片/图像行，我希望按照添加的顺序加载它们，最新的帖子位于顶部。我认为默认情况下使用queryOrderedByKey执行此操作，这是我在获取功能中使用的内容，但帖子无序。

这就是我目前提取帖子的方式：

func fetchPosts() {

    let ref = FIRDatabase.database().reference()
    ref.child("users").queryOrderedByKey().observe(.value, with: { snapshot in

        let users = snapshot.value as! [String : AnyObject]

        for (_, value) in users {

            if let uid = value["uid"] as? String {

                if uid == FIRAuth.auth()?.currentUser?.uid {

                    if let followingUsers = value["following"] as? [String : String] {

                        for (_, user) in followingUsers {
                            self.following.append(user)
                        }
                    }
                    self.following.append(FIRAuth.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 poster = post["poster"] as? String, let likes = post["likes"] as? Int, let pathToImage = post["pathToImage"] as? String, let postID = post["postID"] as? String {

                                            posst.poster = poster
                                            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)
                                                }
                                            }
                                            posts.append(posst)
                                        }
                                    }
                                }
                                self.collectionView.reloadData()
                            }
                        }
                    })
                    ref.removeAllObservers()
                }
            }
        }
    })
}

如何让帖子按最新排序？

编辑2：更新 - 现在从最旧的排序 - ＆gt;最新

func fetchPosts() {

    let ref = FIRDatabase.database().reference()
    ref.child("users").queryOrderedByKey().observe(.value, with: { snapshot in

        let users = snapshot.value as! [String : AnyObject]

        for (_, value) in users {

            if let uid = value["uid"] as? String {

                if uid == FIRAuth.auth()?.currentUser?.uid {

                    if let followingUsers = value["following"] as? [String : String] {

                        for (_, user) in followingUsers {
                            self.following.append(user)
                        }
                    }
                    self.following.append(FIRAuth.auth()!.currentUser!.uid)

                    ref.child("posts").queryOrderedByKey().observeSingleEvent(of: .value, with: { (snap) in

                        for postSnapshot in snap.children.allObjects as! [FIRDataSnapshot] {
                            let value = postSnapshot.value as! [String : AnyObject]

                            if let userID = value["userID"] as? String {
                                for each in self.following {
                                    if each == userID {

                                        let posst = Post()
                                        if let poster = value["poster"] as? String, let likes = value["likes"] as? Int, let pathToImage = value["pathToImage"] as? String, let postID = value["postID"] as? String {

                                            posst.poster = poster
                                            posst.likes = likes
                                            posst.pathToImage = pathToImage
                                            posst.postID = postID
                                            posst.userID = userID
                                            if let people = value["peopleWhoLike"] as? [String : AnyObject] {
                                                for (_, person) in people {
                                                    posst.peopleWhoLike.append(person as! String)
                                                }
                                            }
                                            posts.append(posst)
                                        }
                                    }
                                }
                                self.collectionView.reloadData()
                            }
                        }
                    })
                    ref.removeAllObservers()
                }
            }
        }
    })
}

Answer 1

查询以请求的顺序返回匹配子节点的快照。这意味着结果包含三件事：

1. 项目键
2. 项目值
3. 项目相对于彼此的顺序

但是你对快照做的第一件事就是：

ref.child("posts").queryOrderedByKey().observeSingleEvent(of: .value, with: { (snap) in
  let postsSnap = snap.value as! [String : AnyObject]

您将快照转换为字典。字典只有两个空间：键和值。因此，由于字典具有未定义的顺序，因此订单在此时丢失。

按照您请求的顺序访问结果的正确方法是使用快照的内置子集合来迭代它们：

ref.child("posts").queryOrderedByKey().observeSingleEvent(of: .value, with: { (snapshot) in

  for postSnapshot in snapshot.children {
    let value = postSnapshot.value as! [String : AnyObject]

这将按照您查询的顺序循环匹配的子项。