ios - NSUserDefaults 和我自己的链表实现

Question

我正在创建应用程序，我需要在其中获取最近 10 次搜索的列表并保存它(以在应用程序启动之间显示一致的信息)。

为此，我创建了链表(LinkedList 和 Node 类)的实现以及某种包装类，将其维护为最近 10 个字符串的列表。我使所有这 3 个类都符合 NSCoding 协议(protocol)，并且当需要将其保存为 NSUserDefaults 时它就可以工作。不幸的是，当我尝试加载它时，应用程序崩溃并出现错误:

Terminating app due to uncaught exception 'NSInvalidUnarchiveOperationException', reason: '*** -[NSKeyedUnarchiver decodeObjectForKey:]: cannot decode object of class (_TtGC26Informacje_o_organizacjach4NodeSS_) for key (head); the class may be defined in source code or a library that is not linked'

这是所有 3 个类的代码:

类节点

public class Node<T>: NSObject, NSCoding {
var value: T

var next: Node<T>?
var previous: Node<T>?


init(value: T) {
    self.value = value
}

public required init(coder aDecoder: NSCoder) {
    value = aDecoder.decodeObject(forKey: "value") as! T

    next = aDecoder.decodeObject(forKey: "next") as? Node<T>
    previous = aDecoder.decodeObject(forKey: "previous") as? Node<T>
}

public func encode(with aCoder: NSCoder) {
    aCoder.encode(value, forKey: "value")

    aCoder.encode(next, forKey: "next")
    aCoder.encode(previous, forKey: "previous")
}
}

链表类

public class LinkedList<T>: NSObject, NSCoding {
fileprivate var head: Node<T>?
private var tail: Node<T>?

override init() {
    head = nil
    tail  = nil
}

public var isEmpty: Bool {
    return head == nil
}

public var first: Node<T>? {
    return head
}

public var last: Node<T>? {
    return tail
}

public var count: Int {
    var node = head
    var count = 0

    while node != nil {
        count = count + 1
        node = node?.next
    }

    return count
}

public func removeLast() {
    if let lastNode = last {
        remove(node: lastNode)
    }
}

public func appendFirst(value: T) {
    let newNode = Node(value: value)

    if let headNode = head {
        headNode.previous = newNode
        newNode.next = headNode
    } else {
        tail = newNode
    }

    head = newNode
}

public func append(value: T) {
    let newNode = Node(value: value)

    if let tailNode = tail {
        newNode.previous = tailNode
        tailNode.next = newNode
    } else {
        head = newNode
    }

    tail = newNode
}

public func nodeAt(index: Int) -> Node<T>? {
    if index >= 0 {
        var node = head
        var i = index

        while node != nil {
            if i == 0 { return node }
            i -= 1
            node = node!.next
        }
    }

    return nil
}

public func removeAll() {
    head = nil
    tail = nil
}

public func remove(node: Node<T>) -> T {
    let prev = node.previous
    let next = node.next

    if let prev = prev {
        prev.next = next
    } else {
        head = next
    }

    next?.previous = prev

    if next == nil {
        tail = prev
    }

    node.previous = nil
    node.next = nil

    return node.value
}

public required init?(coder aDecoder: NSCoder) {
    head = aDecoder.decodeObject(forKey: "head") as? Node<T>
    tail = aDecoder.decodeObject(forKey: "tail") as? Node<T>
}

public func encode(with aCoder: NSCoder) {
    aCoder.encode(head, forKey: "head")
    aCoder.encode(tail, forKey: "tail")
}
}

最近的类(class)

public class Recents: NSObject, NSCoding {
fileprivate var list: LinkedList<String>

override init() {
    list = LinkedList<String>()
}

public func enqueue(_ element: String) {
    if let node = search(for: element) {
        list.remove(node: node)
    } else {
        if list.count >= 10 {
            list.removeLast()
        }
    }

    list.appendFirst(value: element)
}

func search(for value: String) -> Node<String>? {
    var curr = list.first

    while curr != nil {
        if curr?.value == value {
            return curr
        }

        curr = curr?.next
    }

    return nil
}

public func count() -> Int {
    return list.count
}

public func nodeAt(index: Int) -> String {
    return list.nodeAt(index: index)!.value
}

public var isEmpty: Bool {
    return list.isEmpty
}

public required init(coder aDecoder: NSCoder) {
    list = aDecoder.decodeObject(forKey: "list") as! LinkedList<String>
}

public func encode(with aCoder: NSCoder) {
    aCoder.encode(list, forKey: "list")
}
}


I use this code to load and save data into NSUserDefaults:

    func saveRecents() {
        let savedData = NSKeyedArchiver.archivedData(withRootObject: recents)
        let defaults = UserDefaults.standard
        defaults.set(savedData, forKey: "recents")
    }

    func loadRecents() {
        let defaults = UserDefaults.standard

        if let savedRecents = defaults.object(forKey: "recents") as? Data {
            recents = NSKeyedUnarchiver.unarchiveObject(with: savedRecents) as! Recents
        }
    }

问题出在哪里？

Answer 1

您收到的错误消息:

Terminating app due to uncaught exception 'NSInvalidUnarchiveOperationException', reason: '*** -[NSKeyedUnarchiver decodeObjectForKey:]: cannot decode object of class (_TtGC26Informacje_o_organizacjach4NodeSS_) for key (head); the class may be defined in source code or a library that is not linked'

表明NSKeyedUnarchiver 很难找到具有给定名称的类。正如您所看到的，您的类的 Objective-C 名称非常困惑(_TtGC26Informacje_o_organizacjach4NodeSS_)，因为它使用了仅 Swift 的功能(在本例中为泛型)。事实是，据我所知，这种修改并不稳定，你需要一个存档格式中的类名，你可以保证将来不会改变。所以我要做的就是使用 @objc() 属性提供一个稳定的 Objective-C 名称，以确保类名保持不变。名称是什么并不重要，只要它是唯一的并且不会改变即可。

@objc(MyApp_Node) public class Node<S>: NSObject, NSCoding {

我不能保证这会解决问题，但它可能会解决问题，而且无论您是否要依赖 NSCoding，这都是您需要做的事情。

编辑:事实证明 @objc 不适用于具有泛型参数的类。所以答案很简单，NSCoding 支持和通用参数是互斥的。您将需要牺牲其中之一(幸运的是，Swift 4 有 Codable，您可以使用它来代替 NSCoding)。