按顺序对数据进行排序

Question

我有一个从 Firebase 获取数据的函数。功能是：

private var levelsArr = [Level]()
func fetchLevels() {

    DataService.instance.levelsRef.observe(.value, with: { (snapshot) in
        print(snapshot)
        if let lvlsDict = snapshot.value as? Dictionary<String, AnyObject> {

            for(_, valueLvl) in lvlsDict {

                if let lvlDict = valueLvl as? Dictionary<String, AnyObject> {
                    if let lvlId = lvlDict["id"] as? Int, let lvlCoverImg = lvlDict["coverImage"] as? String, let lvlTitle = lvlDict["title"] as? String {
                      let level = Level(id: lvlId, coverImage: lvlCoverImg, title: lvlTitle)
                        self.levelsArr.append(level)
                        print(self.levelsArr)
                        DispatchQueue.main.async(execute: { 
                            self.collectionView?.reloadData()
                        })

                    }
                }
            }
        }

    })
    print(self.levelsArr)
}

当我运行应用程序时，控制台会给我这个：

[Repeat.Level(id: 0, coverImage: "lvl0", title: "Level0")]
[Repeat.Level(id: 0, coverImage: "lvl0", title: "Level0"), Repeat.Level(id: 2, coverImage: "lvl2", title: "Level2")]
[Repeat.Level(id: 0, coverImage: "lvl0", title: "Level0"), Repeat.Level(id: 2, coverImage: "lvl2", title: "Level2"), Repeat.Level(id: 3, coverImage: "lvl3", title: "Level3")]
[Repeat.Level(id: 0, coverImage: "lvl0", title: "Level0"), Repeat.Level(id: 2, coverImage: "lvl2", title: "Level2"), Repeat.Level(id: 3, coverImage: "lvl3", title: "Level3"), Repeat.Level(id: 1, coverImage: "lvl1", title: "Level1")]

当我打印快照时，它是有序的，但是当我获取数据并将每个级别放入一个数组时，它不再是有序的。

为什么要这样做，我怎样才能让我的数据像在快照中一样排序？

谢谢。

---

更新

进行以下更改：

    func fetchLevels() {
    DataService.instance.levelsRef.queryOrdered(byChild: "lvlId").observe(.value, with: { (snapshot) in
        print(snapshot)
        if let lvlsDict = snapshot.value as? Dictionary<String, AnyObject> {
            self.levelsArr.removeAll()
            for(_, valueLvl) in lvlsDict {

                if let lvlDict = valueLvl as? Dictionary<String, AnyObject> {
                    if let lvlId = lvlDict["id"] as? Int, let lvlCoverImg = lvlDict["coverImage"] as? String, let lvlTitle = lvlDict["title"] as? String {
                      let level = Level(id: lvlId, coverImage: lvlCoverImg, title: lvlTitle)
                        self.levelsArr.append(level)
                        DispatchQueue.main.async(execute: { 
                            self.collectionView?.reloadData()
                        })
                    }
                }
            }
        }

    })
}



override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {

        // Configure the cell

        let lvlCell = collectionView.dequeueReusableCell(withReuseIdentifier: lvlCellId, for: indexPath) as! lvlCell

        levelsReverseArr = levelsArr.reversed()

        print(levelsReverseArr)
        lvlCell.level = levelsReverseArr[indexPath.item]



        return lvlCell
    }

控制台结果：

Snap (levels) {
level0 =     {
    coverImage = lvl1;
    id = 0;
    title = Level1;
};
level1 =     {
    coverImage = lvl2;
    id = 1;
    title = Level2;
};
level2 =     {
    coverImage = lvl3;
    id = 2;
    title = Level3;
};

[Repeat.Level(id: 1, coverImage: "lvl1", title: "Level1"), Repeat.Level(id: 3, coverImage: "lvl3", title: "Level3"), Repeat.Level(id: 2, coverImage: "lvl2", title: "Level2"), Repeat.Level(id: 0, coverImage: "lvl0", title: "Level0")]

Answer 1

我不完全确定为什么 Firebase 喜欢“搞乱”数组，所以我无法回答您的问题，但要解决此问题，您可以使用 .queryOrdered(byChild:) 来订购快照，更改“id”任何可以订购您的物品的东西：

DataService.instance.levelsRef.queryOrdered(byChild: "id").observe(.value, with: { (snapshot) in

一旦数组已满或更新，您可能还需要反转数组...

更新：

如果你明白我的双关语，这希望应该“排序”你的问题，也就是说，如果 level id 是一个 int 并且你希望它被订购为 lvl 0...100？现在不需要.queryOrdered

func insertionSort<T>(_ arr: [T], _ isOrderedBefore: (T, T) -> Bool) -> [T] {
    guard arr.count > 1 else { return arr }

    var b = arr
    for i in 1..<b.count {
        var y = i
        let temp = b[y]
        while y > 0 && isOrderedBefore(temp, b[y - 1]) {
            b[y] = b[y - 1]
            y -= 1
        }
        b[y] = temp
    }
    return b
}

你需要做的就是改变

levelsReverseArr = levelsArr.reversed()

到

sortedLevelArr = insertionSort(levelArr) { $0.id < $1.id }