ios - Hashable == 方法无法快速检测两个对象之间的差异

Question

我实现了下面的类:

    class Table : Hashable {

    var uid : Int
    var timeRemaining : Int?
    var currentPrice : Double?
    var hashValue: Int {
        return uid.hashValue
    }

    static func ==(lhs: Table, rhs: Table) -> Bool {
        return lhs.uid == rhs.uid && lhs.timeRemaining == rhs.timeRemaining && lhs.currentPrice == rhs.currentPrice
    }

    init (uid: Int, timeRemaining: Int?, currentPrice: Double?) {
        self.uid = uid
        self.timeRemaining = timeRemaining
        self.currentPrice = currentPrice
    }
}

我还定义了这个类的对象数组:

private var tables = [Table]()

接下来，我有以下每秒运行一次的方法:

func updateAuctions() {
    let oldItems = tables
    let newItems = oldItems
    for table in newItems {
        let oldPrice = table.currentPrice!
        let timeRemaining = table.timeRemaining!
        table.currentPrice = oldPrice + 0.50
        table.timeRemaining = timeRemaining - 1
    }
    let changes = diff(old: oldItems, new: newItems)

    collectionView.reload(changes: changes, section: 0) { (complete) in
        if (complete) {
            self.tables = newItems
        }
    }
}

这使用此处描述的 DeepDiff 框架:https://github.com/onmyway133/DeepDiff

我的目标是使用对 tables 数组所做的更改来刷新 UICollectionView，但是框架没有检测到任何更改，即使我的 == 方法检查 timeRemaining 和 currentPrice 是否匹配。

Answer 1

let newItems = oldItems

既然两个数组都包含对象实例，那么它们不就指向相同的对象吗？因此，当您遍历 newItems 并更改值时，您实际上也在更改 oldItems 的值。您可以通过在 for 循环之后打印两个数组的值来验证这一点。

也许你可以试试类似下面的东西？

func updateAuctions() {
    let oldItems = tables
    let newItems = [Table]()
    for item in oldItems {
        newItems.append(Table(uid: item.uid, timeRemaining: item.timeRemaining! - 1, currentPrice: item.currentPrice! + 0.50))
    }
    let changes = diff(old: oldItems, new: newItems)

    collectionView.reload(changes: changes, section: 0) { (complete) in
        if (complete) {
            self.tables = newItems
        }
    }
}