使用查询从 firebase 获取新评论

Question

我有一个在用户刷新页面时调用的 handleRefresh() 函数。当刷新发生时，已发布的新评论将加载到表视图中。

我遇到的问题是，当用户刷新 tableview 中的数据时，加载了两次，所以我得到了更新的评论，但有重复的评论，它再次重新加载了旧评论。

我对如何解决这个问题有点困惑。

这是代码。

var CommentsQuery: DatabaseQuery {
    let postRef = Database.database().reference().child("posts")
    let postKey = keyFound
    let postCommentRef = postRef.child(postKey)
    let lastComment = self.comments.last
    var queryRef: DatabaseQuery
    
    if lastComment == nil {
        queryRef = postCommentRef.queryOrdered(byChild: "timestamp")
    } else {
        let lastTimestamp = lastComment!.createdAt.timeIntervalSince1970 * 1000
        queryRef = postCommentRef.queryOrdered(byChild: "timestamp").queryEnding(atValue: lastTimestamp)
    }
    return queryRef
}


@objc func handleRefresh() {

CommentsQuery.queryLimited(toLast: 20).observeSingleEvent(of: .value) { snapshot in
    
    var tempComments = [Comments]()
    let commentsSnap = snapshot.childSnapshot(forPath: "comments")
    let allComments = commentsSnap.children.allObjects as! [DataSnapshot]
    
    for commentSnap in allComments {
        let degree = commentSnap.childSnapshot(forPath: "reply degree").value as? String ?? ""
        let name = commentSnap.childSnapshot(forPath: "reply name").value as? String ?? ""
        let text = commentSnap.childSnapshot(forPath: "reply text").value as? String ?? ""
        let university = commentSnap.childSnapshot(forPath: "reply university").value as? String ?? ""
        let photoURL = commentSnap.childSnapshot(forPath: "reply url").value as? String ?? ""
        let url = URL(string: photoURL)
        let timestamp = commentSnap.childSnapshot(forPath: "timestamp").value as? Double
        let lastComment = self.comments.last
         
        if snapshot.key == lastComment?.id {
            
            let newComments = Comments(id: snapshot.key, fullname: name, commentText: text, university: university, degree: degree, photoURL: photoURL, url: url!, timestamp: timestamp!)
            
            tempComments.insert(newComments, at: 0)
            print("fetchRefresh")
        }
    }
    self.comments.insert(contentsOf: tempComments, at: 0)
    self.fetchingMore = false
    self.refreshControl.endRefreshing()
    self.tableView.reloadData()
}
  }

Answer 1

如果 self.comments.last 在页面重新加载后仍然存在，那么问题似乎出在您在此处使用 queryEnding(atValue::

queryRef = postCommentRef.queryOrdered(byChild: "timestamp").queryEnding(atValue: lastTimestamp)

由于时间戳值是递增的（值越高越新），您希望节点的时间戳 比最新值高 ，您可以使用 queryStarting(atValue: 和不是 queryEnding(atValue:.

使用查询从 firebase 获取新评论

Fetch new comments from firebase using a query

tableview

firebase

swift

firebase-realtime-database