ios - 分段控件中的表格 View 不会立即显示数据

Question

我有一个分段控件下的表格 View ，表格 View 的数据是从 Firebase 数据库中检索的，代码如下:

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()
        }   
    }
}

数据的检索没有问题。表格 View 和分段控件最初是隐藏的，一旦检索到数据，我就会取消隐藏它们。

问题是表格 View 中的数据没有立即显示，我必须转到另一个选项卡并返回(我的分段控件中有 2 个选项卡)，然后数据才会显示在表格 View 中.我还添加了数据库的图片。





更新

这是我在马特的帮助下尝试过的:

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

幽默我，试试这个。不要隐藏表格 View ，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 Controller 加载个人资料照片的异步。我在这里可能是错的，因为我无法针对 firebase 对其进行测试，但这与我正在做的事情相似。

    func retrieveParticipatedData() {

    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 // should this be "append()" instead of "="? if not why not just call self.participatedStories.append(story) above instead?
                    self.tableView.reloadData()
                }
            }
        }
    }
}