ios - 如何在用户默认中保存对象列表？

Question

我的目标是:

 struct Order: Codable {
        var item_id:String = ""
        var quantity:Int = 0
        var image:String = ""
        var name:String = ""
        var desc:String = ""
    }

函数类是:

    class func saveOrder(value: [Order]) {
        print(value)
        let placesData = NSKeyedArchiver.archivedData(withRootObject: value)
        UserDefaults.standard.set(placesData, forKey: "orderHistoryArray")
    }

    class func getOrder() -> [Order] {
        if let order = UserDefaults.standard.array(forKey: "orderHistoryArray") {
            return order as! [Order]
        }
        return []
    }

当我尝试使用此功能时:

            SavedData.saveOrder(value: itemsInCart)

它对我不起作用，有什么帮助吗？!!!

Answer 1

您正在混淆协议(protocol) Codable 和 NSCoding

1) NS编码

NSKeyed(Un)Archiver 属于 NSCoding。要使用它，您必须将 Order 声明为继承自 NSObject 的 class 并采用协议(protocol)及其所需的方法

class Order: NSObject, NSCoding {
    var item_id : String // no need to assign default values
    var quantity : Int
    var image : String
    var name : String
    var desc : String

    required init(coder decoder: NSCoder) 
    {
        item_id = decoder.decodeObject(forKey: "item_id") as! String
        quantity = decoder.decodeInteger(forKey: "quantity")
        image = decoder.decodeObject(forKey: "image") as! String
        name = decoder.decodeObject(forKey: "name") as! String
        desc = decoder.decodeObject(forKey: "desc") as! String
    }

    func encode(with coder: NSCoder) 
    { 
        coder.encode(item_id, forKey: "item_id")
        coder.encode(quantity, forKey: "quantity")
        coder.encode(image, forKey: "image")
        coder.encode(name, forKey: "name")
        coder.encode(desc, forKey: "desc")
    }
}

然后就可以加载和保存数据了

class func saveOrder(value: [Order]) {
    print(value)
    let placesData = NSKeyedArchiver.archivedData(withRootObject: value)
    UserDefaults.standard.set(placesData, forKey: "orderHistoryArray")
}

class func getOrder() -> [Order] {
    guard let orderData = UserDefaults.standard.data(forKey: "orderHistoryArray"),
          let order = NSKeyedUnarchiver.unarchiveObject(with: orderData) as? [Order] else { return [] }
    return order
}

2) 可编码

使用 Codable，您可以保留您的结构。只需采用协议(protocol)并将编码器创建的Data保存到磁盘

struct Order : Codable {
    var item_id : String
    var quantity : Int
    var image : String
    var name : String
    var desc : String
}

// Both methods `throw` to hand over an en-/decoding error to the caller
class func saveOrder(value: [Order]) throws {
    print(value)
    let placesData = try JSONEncoder().encode(value) else { return }
    UserDefaults.standard.set(placesData, forKey: "orderHistoryArray")
}

class func getOrder() throws -> [Order] {
    guard let orderData = UserDefaults.standard.data(forKey: "orderHistoryArray") else { return [] }
    return try JSONDecoder().decode([Order].self, from: orderData)
}