Question

我会尽力解释我在做什么。我有一个无限滚动集合视图，它从我的firebase数据库为每个单元格加载一个值。每次集合视图创建一个单元格时，它会在数据库位置调用.observe并获取一个Snapchat。如果它加载任何值，它会将单元格背景设置为黑色。黑色背景=从数据库加载的单元格。如果您查看下面的图像，您可以看出并非所有单元格都是从数据库加载的。数据库可以不处理这么多次调用吗？这是一个线程问题吗？我正在做什么与firebase一起工作？截至目前，我将firebase称为my 覆盖func collectionView（_ collectionView：UICollectionView，cellForItemAt indexPath：IndexPath） - ＆gt; UICollectionViewCell { 方法

经过一些测试后，似乎它正在加载firebase中的所有内容，但它并没有更新UI。这导致我相信它在出于某种原因加载信息之前创建了单元格？我将尝试弄清楚如何以某种方式使其“阻止”。

The image

Answer 1

您应该将加载委托给单元格本身，而不是collectionView：cellForItemAtIndexPath方法。原因是委托方法将异步挂起并用于FireBase网络任务的回调。虽然后者通常很快（根据经验），但您可能在此处遇到一些UI加载问题。根据您视图中的方块数判断..

理想情况下，你需要这样的东西：

import FirebaseDatabase


class FirebaseNode {

    //This allows you to set a single point of reference for Firebase Database accross your app
    static let ref = Database.database().reference(fromURL: "Your Firebase URL")

}

class BasicCell : UICollectionViewCell {

    var firPathObserver : String { //This will make sure that as soon as you set the value, it will fetch from firebase
        didSet {
            let path = firPathObserver
            FirebaseNode.ref.thePathToYouDoc(path) ..... {
                snapshot _
                self.handleSnapshot(snapshot)
            }
        }
    }

    override init(frame: CGRect) {
        super.init(frame: frame)
        setupSubViews()
    }

    func setupSubViews() {
        //you add your views here..
    }

    func handleSnapshot(_ snapshot: FIRSnapshot) {
        //use the content of the observed value
        DispatchQueue.main.async {
            //handle UI updates/animations here
        }
    }

}

你会用它：

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let path = someWhereThatStoresThePath(indexPath.item)//you get your observer ID according to indexPath.item.. in whichever way you do this
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Your Cell ID", for: indexPath) as! BasicCell
        cell.firPathObserver = path
        return cell
    }

如果这不起作用，很可能您遇到了一些Firebase限制......这种情况不太可能发生。

更新..带有一些更正和本地缓存。

class FirebaseNode {

    //This allows you to set a single point of reference for Firebase Database accross your app
    static let node = FirebaseNode()

    let ref = Database.database().reference(fromURL: "Your Firebase URL")

    //This is the cache, set to private, since type casting between String and NSString would add messiness to your code
    private var cache2 = NSCache<NSString, DataSnapshot>()

    func getSnapshotWith(_ id: String) -> DataSnapshot? {
        let identifier = id as NSString
        return cache2.object(forKey: identifier)
    }

    func addSnapToCache(_ id: String,_ snapshot: DataSnapshot) {
        cache2.setObject(snapshot, forKey: id as NSString)
    }

}

class BasicCell : UICollectionViewCell {

    var firPathObserver : String? { //This will make sure that as soon as you set the value, it will fetch from firebase
        didSet {
            handleFirebaseContent(self.firPathObserver)
        }
    }

    override init(frame: CGRect) {
        super.init(frame: frame)
        setupSubViews()
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    func setupSubViews() {
        //you add your views here..
    }

    func handleFirebaseContent(_ atPath: String?) {
        guard let path = atPath else {
            //there is no content
            handleNoPath()
            return
        }
        if let localSnap = FirebaseNode.node.getSnapshotWith(path) {
            handleSnapshot(localSnap)
            return
        }
        makeFirebaseNetworkTaskFor(path)
    }


    func handleSnapshot(_ snapshot: DataSnapshot) {
        //use the content of the observed value, create and apply vars
        DispatchQueue.main.async {
            //handle UI updates/animations here
        }
    }

    private func handleNoPath() {
        //make the change.
    }

    private func makeFirebaseNetworkTaskFor(_ id: String) {
        FirebaseNode.node.ref.child("go all the way to your object tree...").child(id).observeSingleEvent(of: .value, with: {
            (snapshot) in

            //Add the conditional logic here..

            //If snapshot != "<null>"
            FirebaseNode.node.addSnapToCache(id, snapshot)
            self.handleSnapshot(snapshot)
            //If snapshot == "<null>"
            return

        }, withCancel: nil)
    }

}

然而，有一点，使用NSCache：这适用于中小型列表或内容范围;但是它有一个内存管理功能，如果内存变得稀缺，它可以解除内容。所以当处理像你这样的大集合时，你也可以选择使用分类字典，因为它的内存不会自动解除分配。使用它就像换掉东西一样简单：

class FirebaseNode {

    //This allows you to set a single point of reference for Firebase Database accross your app
    static let node = FirebaseNode()

    let ref = Database.database().reference(fromURL: "Your Firebase URL")

    //This is the cache, set to private, since type casting between String and NSString would add messiness to your code
    private var cache2 : [String:DataSnapshot] = [:]

    func getSnapshotWith(_ id: String) -> DataSnapshot? {
        return cache2[id]
    }

    func addSnapToCache(_ id: String,_ snapshot: DataSnapshot) {
        cache2[id] = snapshot
    }

}

此外，请务必确保完成对node的{{1}}强引用，这可确保您始终使用Firebasenode的ONE实例。即，这没关系：Firebasenode或Firebasenode.node.ref，这不是：Firebasenode.node.getSnapshot..或Firebasenode.ref

如何从Firebase正确加载信息？

1 个答案: