分段控件中的表视图不会立即显示数据

Question

我有一个处于分段控制之下的表视图，该表视图的数据是从Firebase数据库中检索的，下面是代码：

func retrieveParticipatedData(completion: @escaping (Bool) -> Void) {

    let storyIDRef = DBRef.child("Story IDs").child(userID!)
    var participatedStoryItems: [ParticipatedStoriesPageData] = []

    storyIDRef.observeSingleEvent(of: .value) { (snapshot) in
        if let dict = snapshot.value as? [String : String] {

            for (_, value) in dict {

                self.DBRef.child("To be reviewed stories").child(value).observeSingleEvent(of: .value) { (snapshot) in
                    if let storyDict = snapshot.value as? [String : Any] {

                        let storyTitle = storyDict["Book Title"] as? String
                        let storyDescription = storyDict["Description"] as? String
                        let storyID = value
                        let votes = storyDict["Votes"] as? Int

                        let story = ParticipatedStoriesPageData(storyKey: storyID, storyTitle: storyTitle!, storyDescription: storyDescription!, votes: votes!)
                        participatedStoryItems.append(story)
                    }
                    self.participatedStories = participatedStoryItems
                    completion(true)
                }
            }
        }
    }
}

override func viewDidLoad() {
    super.viewDidLoad()

    retrieveParticipatedData { (isRetreived) in

        if isRetreived {
            self.tableView.isHidden = false
            self.tableView.reloadData()
        }   
    }
}

数据检索没有问题。最初隐藏了表视图和分段控件，并且一旦检索到数据，便取消隐藏它们。

问题是表格视图中的数据不会立即显示，我必须转到另一个选项卡然后返回（我的分段控件中有2个选项卡），然后数据才显示在表格视图。我还添加了数据库图片。

更新

这是我在Matt的帮助下尝试的内容：

func retrieveParticipatedData() {

    let dispatchGroup = DispatchGroup()
    let storyIDRef = DBRef.child("Story IDs").child(userID!)
    var participatedStoryItems: [ParticipatedStoriesPageData] = []

    storyIDRef.observeSingleEvent(of: .value) { (snapshot) in
        if let dict = snapshot.value as? [String : String] {
            for (_, value) in dict {
                self.DBRef.child("To be reviewed stories").child(value).child("Participants").child("Chapter 1 Author").observeSingleEvent(of: .value) { (snapshot) in

                    if snapshot.value as? String == self.userID {
                        dispatchGroup.enter()

                        self.DBRef.child("To be reviewed stories").child(value).observeSingleEvent(of: .value) { (snapshot) in
                            if let storyDict = snapshot.value as? [String : Any] {

                                let storyTitle = storyDict["Book Title"] as? String
                                let storyDescription = storyDict["Description"] as? String
                                let storyID = value
                                let votes = storyDict["Votes"] as? Int

                                let story = ParticipatedStoriesPageData(storyKey: storyID, storyTitle: storyTitle!, storyDescription: storyDescription!, votes: votes!)
                                participatedStoryItems.append(story)
                            }
                            self.participatedStories = participatedStoryItems.reversed()
                            dispatchGroup.leave()
                        }
                        dispatchGroup.notify(queue: .main) {
                            print("Retrieved")
                            self.tableView.reloadData()
                        }
                        // It works if I do this
                        /*dispatchGroup.notify(queue: .main) {
                            print("Retrieved")
                            self.setupTableView // Creates the table view
                        }*/
                        //But I don't wanna do this cuz then there would be no table view if there is no data retreived.
                    }
                }
            }
        }
    }
}

override func viewDidLoad() {
    super.viewDidLoad()

    retrieveParticipatedData()
    setupStackView()
    setupTableView()  // Creates the table view
}

Answer 1

请让我尝试一下。不要隐藏表格视图，只需在viewDidLoad（）中调用此函数即可。对于我的应用程序，我正在下载一长串用户，并使用分段控制器来加载个人资料照片的异步操作。我在这里可能是错的，因为我无法针对Firebase进行测试，但这与我正在执行的操作类似。