swift - 如何从 firebase 异步加载数据并将其显示在 UICollectionView 中

Question

我尝试显示已登录用户关注的用户的用户名。仅详细介绍那些在简单的 UICollectionView 中也有故事(如 Snapchat)的人。所以我需要该人的用户名在该单元格中显示为简单的标签。为了实现这一点，我认为我可以简单地将所有具有故事的内容添加到数组中，然后获取第一个故事的第一个项目，第二个故事的第二个项目，依此类推......但正如我之前提到的，我想检索并显示用户名。现在的问题是“cellForItemAt”函数没有等待从 firebase 检索到的数据填充数组，因此它使用空的 self.storyNames 数组以及 return self.storyNames.count 等于 0。

class HomeViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource {

    @IBOutlet weak var collectionView_stories: UICollectionView!

    var storyNames: [String] = []

    override func viewDidLoad() {
        super.viewDidLoad()

        collectionView_stories.delegate = self
        collectionView_stories.dataSource = self
        collectionView_stories.showsHorizontalScrollIndicator = false

        getStoryNames() { storyNames in
            self.storyNames = storyNames
            DispatchQueue.main.async {
                self.collectionView_stories.reloadData()
            }
        }
    }

    @IBAction func barButton_camera_pressed(_ sender: Any) {
    }

    @IBAction func barButton_inbox_pressed(_ sender: Any) {
    }

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return self.storyNames.count
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let story_cell = collectionView_stories.dequeueReusableCell(withReuseIdentifier: "stories_cell", for: indexPath) as? StoryCollectionViewCell

        story_cell?.imageView_story.layer.cornerRadius = (story_cell?.imageView_story.frame.size.width)! / 2
        story_cell?.imageView_story.clipsToBounds = true
        story_cell?.imageView_story.layer.shadowColor = UIColor.black.cgColor
        story_cell?.imageView_story.layer.shadowRadius = 3
        story_cell?.imageView_story.layer.shadowOpacity = 0.6
        story_cell?.imageView_story.layer.borderWidth = 1.0
        story_cell?.imageView_story.layer.borderColor = UIColor.darkGray.cgColor
        story_cell?.imageView_story.image = UIImage(named: "bitmoji")

        story_cell?.label_username.text = self.storyNames[indexPath.row]

        return story_cell!
    }

    func getStoryNames(completion: @escaping ([String]) -> ()) {
        var tempStoryNames: [String] = []
        let userID = Auth.auth().currentUser?.uid
        Database.database().reference().child("subscriptions").child(userID!).observeSingleEvent(of: .value) { snapshot in
            let dispatchGroup = DispatchGroup()
            for child in snapshot.children.allObjects as! [DataSnapshot] {
                let dict = child.value as! String
                Database.database().reference().child("users").child(dict).child("hasStory").observeSingleEvent(of: .value) { snapshot in
                    if let item = snapshot.value as? Bool {
                        if (item == true) {
                            dispatchGroup.enter()
                            Database.database().reference().child("users").child(dict).child("username").observeSingleEvent(of: .value) { snapshot in
                                let aaa = snapshot.value as! String
                                tempStoryNames.append(aaa)
                                print(tempStoryNames)
                            }
                        }
                    }
                    dispatchGroup.leave()
                }
            }
            dispatchGroup.notify(queue: .main) {
                completion(tempStoryNames)
            }
        }
    }
}

您知道如何解决这个问题吗？我已尽力而为，也知道这不是最好的代码，但我正在努力，因此我真的需要您的帮助。我感谢每一个答案!

Answer 1

在numberOfItemsInSection中，您应该依赖于storyNames的长度，这将确保您的数据正确显示

func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
    return self.storyNames.count
}