swift - 仅在从 firebase 数据库 Swift 下载所有内容后才重新加载 TableView 数据

Question

我已经找了一段时间了，但我不知道如何处理这个问题。我有一个 Firebase 数据库，其中包含一些数据和存储在存储中的图像链接。我希望我的 UICollectionView 在从数据库下载完每张图片后重新加载，而不仅仅是第一张。

newRef.observeSingleEvent(of: .value, with: { (snapshotOne) in
        for child in snapshotOne.children {
            let snap = child as! DataSnapshot
            let key = snap.key

            newRef.child(key).observeSingleEvent(of: .value, with: { (snapshotTwo) in
                for child in snapshotTwo.children {
                    let snappotto = child as! DataSnapshot
                    var imageDownloaded: UIImage?

                    if let dictionary = snappotto.value as? [String : AnyObject] {
                        let url = URL(string: dictionary["imageURL"] as! String)
                        URLSession.shared.dataTask(with: url!) { (data, response, error) in
                            if error != nil {
                                print("[Error]: \(String(describing: error))")
                                return
                            }

                            imageDownloaded = UIImage(data: data!)

                            let person = Person(name: dictionary["name"] as! String, surname: dictionary["surname"] as! String, tags: [.castana], image: imageDownloaded!)
                            self.storedData.append(person)

                            self.filteredData = self.storedData

                            DispatchQueue.main.sync {
                                UIApplication.shared.endIgnoringInteractionEvents()
                                self.collectionView.reloadData()
                                self.dismiss(animated: false, completion: nil)
                            }

                        }.resume()
                    }
                }
            }) { (error) in
                print("[Error]: \(String(describing: error))")
            }
        }
    }) { (error) in
        print("[Error]: \(error)")
    }

这是我使用的代码，但这会在仅下载第一张图像后更新我的 UICollectionView，并随之结束 IgnoringInteractionEvents - 并允许用户一次又一次地重新加载数据，这会导致大量图像重复。

在下载完数据库中的每个项目后，如何移动重新加载和 endIgnoringInteractionEvents？

数据库结构如下:

| folder
-| user
--| autoId
---| name
---| surname
---| imageUrl
--|autoId
---| name
---| surname
---| imageUrl
-| user
--| autoId
---| name
---| surname
---| imageUrl

非常感谢，NicopDev

Answer 1

您在嵌套数据上嵌套观察者，这似乎是一种代码浪费。当您将观察者附加到某个位置时，该位置下的所有数据都已加载。

因此您可以循环遍历嵌套快照以获得相同的结果:

newRef.observeSingleEvent(of: .value, with: { (snapshot) in
    for child in snapshot.children {
        let userSnapshot = child as! DataSnapshot
        let userKey = userSnapshot.key

        for child in userSnapshot.children {
            let imageSnapshot = child as! DataSnapshot
            var imageDownloaded: UIImage?
            ...

---

说完这些，让我们继续讨论您的真正问题:您如何检测所有图像何时已加载。

一种简单的跨平台方法是简单地计算您已加载的图像数量，并将其与您知道存在的图像数量进行比较。由于您有一棵仅包含现有图像的树，因此您可以在双重嵌套结构的迭代中同时执行这两项操作

let knownImageCount = 0 // we start with no knowledge of any image
let loadedImageCount = 0 // we also haven't loaded any image yet

for child in snapshot.children {
    let userSnapshot = child as! DataSnapshot
    let userKey = userSnapshot.key

    knownImageCount = knownImageCount + userSnapshot.childrenCount // we've found out about N more images

    for child in userSnapshot.children {
        let imageSnapshot = child as! DataSnapshot
        var imageDownloaded: UIImage?
        ...

        URLSession.shared.dataTask(with: url!) { (data, response, error) in

            ...

            loadedImageCount = loadedImageCount + 1 // we loaded an additional image

            if loadedImageCount == knownImageCount {
                ... // we've loaded all known images, we're done!
            }
        }.resume()