如何从Firebase正确加载信息？-Java 学习之路

我会尽力解释我在使用firebase工作的时间吗？截至目前，我在 override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell { 方法中调用了firebase

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

1 回答

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 . 根据视图中的方块数判断..

理想情况下，你想要这样的东西：

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，很可能您可能遇到一些Firebase限制..这是不太可能的imo .

Update .. with some corrections and with local cache .

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，可以对内容进行去内核处理 . 所以当处理像你这样的大集合时，你可能会选择使用分类字典，因为它的内存不会自动解除分配 . 使用它就像交换东西一样简单：

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，始终确保通过 node 强引用 Firebasenode ，这可确保您始终使用 Firebasenode 的ONE实例 . 即，这没关系： Firebasenode.node.ref 或 Firebasenode.node.getSnapshot.. ，这不是： Firebasenode.ref 或 Firebasenode().ref

回复于 2024-05-15T10:13:42+08:00

如何从Firebase正确加载信息？

1 回答

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