Swift 3：将数组保存到 UserDefaults 错误 - 对象数与键数不同

Question

我的应用程序因错误而崩溃：

由于未捕获的异常“NSInvalidArgumentException”而终止应用程序，原因：“*** -[NSDictionary initWithObjects:forKeys:]：对象数 (0) 与键数 (1) 不同

这是我保存var favoriteAppAnnotations = [Int: AppAnnotation]()的方法：

let userDefaults = UserDefaults.standard
let favoritesData: Data = NSKeyedArchiver.archivedData(withRootObject: self.favoriteAppAnnotations)
userDefaults.set(favoritesData, forKey: "FAVORITES")
userDefaults.synchronize()

这是我的加载方式：

self.favoriteAppAnnotations = [:]
let userDefaults = UserDefaults.standard
if let decoded = userDefaults.object(forKey: "FAVORITES") as? Data {
   let favoritesArray = NSKeyedUnarchiver.unarchiveObject(with: decoded) as! [Int: AppAnnotation] // THIS IS WHERE THE CRASH IS
   if favoritesArray.isEmpty == false {
       self.favoriteAppAnnotations = favoritesArray
   }
}

AppAnnotation 符合 NSCoding 如下：

    class AppAnnotation: ParentAppAnnotation, NSCoding // Note: ParentAppAnnotation is NSObject but doe snot conform to NSCoding
    {
        open var placeId: Int?
        open var placeName: String?
        open var placeDescription: String?
        override init() {
            super.init()
        }
        init(placeId: Int, placeName: String, placeDescription: String) {
            self.placeId = placeId
            self.placeName = placeName
            self.placeDescription = placeDescription
        }
        required convenience init?(coder decoder: NSCoder) {
            guard let placeName = decoder.decodeObject(forKey: "placeName") as? String,
                  let placeDescription = decoder.decodeObject(forKey: "placeDescription") as? String
                  else { return nil }
            self.init(placeId: decoder.decodeInteger(forKey: "placeId"),
                    placeName: placeName,
                    placeDescription: placeDescription)

        }
        func encode(with coder: NSCoder) {
            coder.encodeCInt(Int32(self.placeId!), forKey: "placeId")
            coder.encode(self.placeName, forKey: "placeName")
            coder.encode(self.placeDescription, forKey: "placeDescription")
        }
    }

我放弃了问题所在。考虑保存数组的替代方法...例如转换为JSON 字符串。
但我想了解当前的问题可能出在哪里。

Answer 1

强制展开的问题。

NSKeyedUnarchiver.unarchiveObject(with: decoded) as! [Int: AppAnnotation]

使用

NSKeyedUnarchiver.unarchiveObject(with: decoded) as? [Int: AppAnnotation]

查看方法定义：

open class func unarchiveObject(with data: Data) -> Any?

它返回可选值。