[英]Class conforming to Codable protocol fails with encodeWithCoder: unrecognized selector sent to instance
[英]Trying to archive an instance of a class conforming to NSCoder
我正在開發我的第一個Swift iOS應用程序,無法序列化和保存從服務器獲取其JSON的對象。 我正在使用Gloss ,這是一個輕量級的JSON解析庫,該庫定義了Decodable協議,通過該協議可以從JSON實例化實例。 我的意圖是通過首先提取其ID從JSON
( [String : AnyObject]
的類型別名)中加載事物,然后檢查是否已具有本地存檔副本。 如果這樣做,請取消存檔並獲取圖像。 如果不是,則對圖像文件發出異步請求。
問題在於Thing.localArchiveExists(id)
始終返回false
。 事物已成功實例化,但是它們總是重新獲取圖像。 我已經檢查了文件系統,並確認沒有歸檔文件正在寫入。 但是,我沒有看到“錯誤。無法存檔”,這向我提示保存成功。 我是否缺少有關如何存檔和保存NSCoder對象的內容? 謝謝!
這是我對“可解碼協議”的實現:
// MARK: Decodable protocol
// When a thing is loaded from JSON, we load its image from archive if possible.
required init?(json: JSON) {
guard let id: Int = "id" <~~ json else { return nil}
if Thing.localArchiveExists(id) {
guard let savedThing = NSKeyedUnarchiver.unarchiveObjectWithFile(Thing.archiveFilePath(id)) as? Thing else { return nil }
self.id = savedThing.id
self.name = savedThing.name
self.image = savedThing.image
self.imageUrl = savedThing.imageUrl
super.init()
print("Loaded Thing \(self.name) from archive")
}
else {
guard let name: String = "name" <~~ json else { return nil}
guard let imageUrl: NSURL = "url" <~~ json else { return nil}
self.id = id
self.name = name
self.imageUrl = imageUrl
super.init()
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)) {
let data = NSData(contentsOfURL: imageUrl)
dispatch_async(dispatch_get_main_queue(), {
self.image = UIImage(data: data!)
guard self.save() else {
print("ERROR. Could not archive")
return
}
print("Loaded Thing \(self.name) from server")
})
}
}
}
以下是Thing類的相關部分:
// MARK: Properties
var id: Int?
var name: String
var imageUrl: NSURL?
var image: UIImage?
// MARK: Archiving Paths
static let DocumentsDirectory = NSFileManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask).first!
static let ArchiveURL = DocumentsDirectory.URLByAppendingPathComponent("things")
// MARK: Types
struct PropertyKey {
static let nameKey = "name"
static let imageKey = "image"
static let imageUrlKey = "imageUrl"
static let idKey = "id"
}
// Returns the file URL at which a Thing with the given ID should be saved.
class func archiveFilePath(id: Int) -> String {
return Thing.ArchiveURL.URLByAppendingPathComponent("thing\(id)").absoluteString
}
// Checks whether an archived copy of a Thing with the given ID exists.
class func localArchiveExists(id: Int) -> Bool {
let fileManager = NSFileManager.defaultManager()
return fileManager.fileExistsAtPath(Thing.archiveFilePath(id))
}
// MARK: NSCoding
func encodeWithCoder(coder: NSCoder) {
coder.encodeObject(name, forKey: PropertyKey.nameKey)
if image != nil {
coder.encodeObject(image!, forKey: PropertyKey.imageKey)
}
if imageUrl != nil {
coder.encodeObject(imageUrl!, forKey: PropertyKey.imageUrlKey)
}
coder.encodeInteger(id!, forKey: PropertyKey.idKey)
}
required convenience init?(coder aDecoder: NSCoder) {
let name = aDecoder.decodeObjectForKey(PropertyKey.nameKey) as! String
let image = aDecoder.decodeObjectForKey(PropertyKey.imageKey) as? UIImage
let imageUrl = aDecoder.decodeObjectForKey(PropertyKey.imageUrlKey) as? NSURL
let id = aDecoder.decodeIntegerForKey(PropertyKey.idKey)
// Must call designated initializer.
self.init(name: name, image: image, imageUrl: imageUrl, id: id)
}
func save() -> Bool {
// For some reason I can't archive to file.
return NSKeyedArchiver.archiveRootObject(self, toFile: Thing.archiveFilePath(self.id!))
}
我發現了我的問題:保存失敗,因為我還沒有創建試圖保存Thing的目錄。
func save() -> Bool {
let archivedData = NSKeyedArchiver.archivedDataWithRootObject(self)
do {
try NSFileManager.defaultManager().createDirectoryAtURL(Thing.ArchiveURL, withIntermediateDirectories: true, attributes: [:])
try archivedData.writeToFile(Thing.archiveFilePath(self.id!), options: [])
return true
} catch {
print(error)
return false
}
}
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