ios - 调用注释填充TableView : correcting code errors

Question

我正在尝试用我的帖子中的评论填充我的评论表。我有以下数据库结构 JSON:

  {
  "posts" : {
    "-Lhu-XRs806sXSEQS2BF" : {
      "reports" : 0,
      "text" : "How can I improve my data structure?",
      "timestamp" : 1561120090116,
      "title" : "Hello Stack Exchange",
      "userID" : "nyRBXSyyDhc1Qkypou0Iz0iMsyr1"
    },
    "-Lhu-fI6DMSZvy8EdIgM" : {
      "reports" : 0,
      "text" : "As in Libre",
      "timestamp" : 1561120126347,
      "title" : "Free",
      "userID" : "nyRBXSyyDhc1Qkypou0Iz0iMsyr1"
    },
    "comments" : {
      "-Lhu-hXISy-0N2V4ES-a" : {
        "reports" : 0,
        "timestamp" : 1561120135594,
        "userID" : "nyRBXSyyDhc1Qkypou0Iz0iMsyr1"
      },
      "-Lhu-j1cR6V407tyUYY1" : {
        "reports" : 0,
        "timestamp" : 1561120141801,
        "userID" : "nyRBXSyyDhc1Qkypou0Iz0iMsyr1"
      },
      "-Lhu-lrJp9H8SQowlYWz" : {
        "reports" : 0,
        "timestamp" : 1561120153314,
        "userID" : "nyRBXSyyDhc1Qkypou0Iz0iMsyr1"
      },
      "posts" : {
        "-Lhu-XRs806sXSEQS2BF" : {
          "comments" : {
            "-Lhu-hXISy-0N2V4ES-_" : "How is it going?",
            "-Lhu-j1cR6V407tyUYY0" : "It’s good to see you"
          }
        },
        "-Lhu-fI6DMSZvy8EdIgM" : {
          "comments" : {
            "-Lhu-lrJp9H8SQowlYWy" : "Richard Stallman"
          }
        }
      }
    }
  }
}

以及以下 Comment 类:

class Comment {
    var id:String
    var text:String

    init(id: String, text:String) {
        self.id = id
        self.text = text
    }
}

这是考虑了您的建议后我的代码:

var comments = [Comment] ()
@IBOutlet weak var commentsTable: UITableView!
@IBOutlet weak var commentPlaceHolder: UILabel!
@IBOutlet weak var newCommentLabel: UITextView!
weak var delegate:NewPostVCDelegate?
let ref = Database.database().reference().child("posts")

@IBAction func reply(_ sender: UIButton) {
    let userID = (Auth.auth().currentUser?.uid)!
    addComment(toPostId: post!.id, andComment: newCommentLabel.text, commentByUid: userID)
    loadComments(forPostId: post!.id)
    comments.removeAll()
    commentsTable.reloadData()
    newCommentLabel.text = String()
    commentPlaceHolder.isHidden = false
}

func addComment(toPostId: String, andComment: String, commentByUid: String) {
    let commentsRef = self.ref.child("comments") //ref to the comments node
    let thisCommentRef = commentsRef.child(toPostId) //ref to a node with postId as key
    let commentToAddRef = thisCommentRef.childByAutoId() //each comment will have it's own key
    let d = [
        "comment_text": andComment,
        "comment_by_uid": commentByUid]
    commentToAddRef.setValue(d)
}

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    loadComments(forPostId: post!.id)
}

func loadComments(forPostId: String) {
    let ref = self.ref.child("comments")
    let thisPostRef = ref.child(forPostId)
    thisPostRef.observeSingleEvent(of: .value, with: { snapshot in

        let allComments = snapshot.children.allObjects as! [DataSnapshot]
        for commentSnap in allComments {
            let commenterUid = commentSnap.childSnapshot(forPath: "comment_by_uid").value as? String ?? "No uid"
            let commentText = commentSnap.childSnapshot(forPath: "comment_text").value as? String ?? "No comment"
            let aComment = Comment(id: commenterUid, text: commentText)
            self.comments.append(aComment)
            print(commenterUid, commentText)
        }
        self.commentsTable.reloadData()
    })
}

func adjustUITextViewHeight(arg : UITextView) {
    arg.translatesAutoresizingMaskIntoConstraints = true
    arg.sizeToFit()
    arg.isScrollEnabled = false
}

override func viewDidLoad() {
    super.viewDidLoad()
    self.commentsTable.dataSource = self
    let cellNib = UINib(nibName: "CommentTableViewCell", bundle: nil)
    commentsTable.register(cellNib, forCellReuseIdentifier: "postCell")
    view.addSubview(commentsTable)
    commentsTable.register(LoadingCell.self, forCellReuseIdentifier: "loadingCell")

    self.commentsTable.delegate = self
    mainText.isEditable = false
    titleText.isEditable = false
    commentsTable.register(cellNib, forCellReuseIdentifier: "postCell")
    view.addSubview(commentsTable)
    commentsTable.register(LoadingCell.self, forCellReuseIdentifier: "loadingCell")
    print(delegate!)
}

func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return comments.count
}

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    if indexPath.section == 0 {
        let cell = tableView.dequeueReusableCell(withIdentifier: "postCell", for: indexPath) as! CommentTableViewCell
        cell.set(comment: comments[indexPath.row])
        return cell
    } else {
        let cell = tableView.dequeueReusableCell(withIdentifier: "loadingCell", for: indexPath) as! LoadingCell
        cell.spinner.startAnimating()
        return cell
    }
}

func textViewDidChange(_ commentView: UITextView) {
    commentPlaceHolder.isHidden = !newCommentLabel.text.isEmpty
}

结合杰伊的评论，我开始运行 View 。我必须添加comments.removAll()，这样它就不会在commentsTable中多次打印出评论。但是，func textViewDidChange 不再起作用。我不知道如何解决这个问题。我尝试调用该函数，但没有成功。也许委托(delegate)变更影响了这一点？

Answer 1

此答案基于问题中的数据以及后续评论。

非规范化数据是 NoSQL 数据库中的标准做法，但在这种情况下，问题中的结构可能比所需的更复杂。

问题来了

Given a series of posts where each post has comments, how do you load the comments for each post to be displayed in a tableView.

我将从提议的结构开始逆向工作

posts
   post_0 //created with .childByAutoId
      creator_uid: "the uid of whoever created this post"
      post_title: "My post about posting"

comments
   post_0 //ties back to the key of the post in the posts node
      comment_0 //created with .childByAutoId
         comment_by_uid: "whoever created this comment"
         comment_text: "comment about this post"
      comment_1
         comment_by_uid: "whoever created this comment"
         comment_text: "comment about this post"

此结构将评论与它们引用的帖子分开。在 comments 节点中，每个节点的关键是 posts 节点中的 post_id。这允许将帖子加载到 tableView 中，而不会产生大量开销，例如，如果您在详细 View 中显示评论，则加载特定帖子的所有评论。

请注意，帖子节点和评论节点键是使用 .childByAutoId() 创建的

现在是工作流程。假设用户正在创建新帖子并输入了帖子标题和其他信息。调用此函数可在 Firebase 中创建帖子。

func createPost(withTitle: String, andCreatorUid: String) {
    let postsRef = self.ref.child("posts")
    let thisPost = postsRef.childByAutoId()
    let d = [
        "post_title": withTitle,
        "creator_uid": andCreatorUid
        ]
    thisPost.setValue(d)
}

这里有一个棘手的地方 - 我所做的是有一个 posts 节点的观察者。添加新帖子时，我会收到该事件，创建一个包含有关该帖子的信息的 PostsClass 对象，并将其添加到我的 dataSource 数组中，然后刷新我的 tableView。通过这样做，我还获得了节点的 key (它是使用 .childByAutoId 创建的)。

另一位用户看到该帖子并想要对其发表评论，因此他们点击该帖子以输入评论。以下代码将他们的评论存储在 Firebase 中。

func addComment(toPostId: String, andComment: String, commentByUid: String) {
    let commentsRef = self.ref.child("comments") //ref to the comments node
    let thisCommentRef = commentsRef.child(toPostId) //ref to a node with postId as key
    let commentToAddRef = thisCommentRef.childByAutoId() //each comment will have it's own key
    let d = [
        "comment_text": andComment,
        "comment_by_uid": commentByUid]
    commentToAddRef.setValue(d)
}

toPostId 是帖子的关键，它是从他们选择添加评论的 PostClass 对象获取的。

最后，为了专门回答这个问题，这里加载了特定帖子的评论。

func loadComments(forPostId: String) {
    let ref = self.ref.child("comments")
    let thisPostRef = ref.child(forPostId)
    thisPostRef.observeSingleEvent(of: .value, with: { snapshot in

        let allComments = snapshot.children.allObjects as! [DataSnapshot]
        for commentSnap in allComments {
            let commenterUid = commentSnap.childSnapshot(forPath: "comment_by_uid").value as? String ?? "No uid"
            let commentText = commentSnap.childSnapshot(forPath: "comment_text").value as? String ?? "No comment"
            //create a commentClass object, update properties and add to dataSourceArray
            print(commenterUid, commentText)
        }
        //tableView reload
    })
}

注意事项:

我有一个类 var，ref，因此 self.ref 指向我的根 Firebase 节点。您需要将其设置为指向您的

我在此答案中使用 post_0 和 comment_0 作为节点键名称，因为它比 -LhzJD3tPL0xcnUDMaOZ 这样的键更容易阅读和理解，而 .childByAutoId 将在您的 Firebase 中实际创建。