[英]How to encode and decode struct to NSData in swift?
我有以下結構定義:
struct ThreadManager: Equatable {
let fid: Int
let date: NSDate
let forumName: String
let typeid: Int
var page: Int
var threadList: [Thread]
var totalPageNumber: Int?
}
和線程是:
struct Thread: Equatable {
let author: Author
let replyCount: Int
let readCount: Int
let title: String
let tid: Int
let isTopThread: Bool
var attributedStringDictionary: [String: NSAttributedString]
var postDescripiontTimeString: String
var hasRead: Bool
}
如何將ThreadManager變量編碼為NSData? 我嘗試使用以下功能,但不起作用。
func encode<T>(var value: T) -> NSData {
return withUnsafePointer(&value) { p in
NSData(bytes: p, length: sizeofValue(value))
}
}
func decode<T>(data: NSData) -> T {
let pointer = UnsafeMutablePointer<T>.alloc(sizeof(T))
data.getBytes(pointer, length: sizeof(T))
return pointer.move()
}
我有ThreadManager項,我想將它們存儲到sqlite中。 所以我需要將它們轉換為NSData。 我有一個名為threadManager的變量,其threadList中的項目數約為70。我運行代碼並設置一個斷點,並在xcode控制台中輸入encode(threadManager),它只有73字節。 這是錯誤的。 我如何編碼和解碼那些結構到NSData。
如果要在任何其他平台(Android,Web,無論在何處)上讀取數據庫,則最好選擇跨平台格式(例如JSON),或者將struct成員散布在數據庫表的專用列中。
如果您僅針對iOS / OSX / tvOS / etc,則建議使用NSCoder。 它是有效的,最重要的是:
下面的代碼向您的結構中添加一個asData()
函數,以及一個init(data:)
初始化程序。 這兩個讓您從結構到NSData來回切換。
import Foundation
struct MyStruct {
let name: String
let date: NSDate
}
extension MyStruct {
init(data: NSData) {
let coding = NSKeyedUnarchiver.unarchiveObjectWithData(data) as! Coding
name = coding.name as String
date = coding.date
}
func asData() -> NSData {
return NSKeyedArchiver.archivedDataWithRootObject(Coding(self))
}
class Coding: NSObject, NSCoding {
let name: NSString
let date: NSDate
init(_ myStruct: MyStruct) {
name = myStruct.name
date = myStruct.date
}
required init?(coder aDecoder: NSCoder) {
self.name = aDecoder.decodeObjectForKey("name") as! NSString
self.date = aDecoder.decodeObjectForKey("date") as! NSDate
}
func encodeWithCoder(aCoder: NSCoder) {
aCoder.encodeObject(name, forKey: "name")
aCoder.encodeObject(date, forKey: "date")
}
}
}
let encodedS = MyStruct(name: "foo", date: NSDate())
let data = encodedS.asData()
let decodedS = MyStruct(data: data)
print(decodedS.name)
print(decodedS.date)
@GwendalRoué:您是對的,但是我必須根據每個結構構建另一個類。 我使用了以下方法,這很丑陋,但是可行。 你能幫我改善嗎?
init(data: NSData) {
let dictionary = NSKeyedUnarchiver.unarchiveObjectWithData(data) as! NSDictionary
fid = (dictionary["fid"] as! NSNumber).integerValue
date = dictionary["date"] as! NSDate
forumName = dictionary["forumName"] as! String
typeid = (dictionary["typeid"] as! NSNumber).integerValue
page = (dictionary["page"] as! NSNumber).integerValue
totalPageNumber = (dictionary["totalPageNumber"] as? NSNumber)?.integerValue
let threadDataList = dictionary["threadDataList"] as! [NSData]
threadList = threadDataList.map { Thread(data: $0) }
}
extension ThreadManager {
func encode() -> NSData {
let dictionary = NSMutableDictionary()
dictionary.setObject(NSNumber(integer: fid), forKey: "fid")
dictionary.setObject(date, forKey: "date")
dictionary.setObject(forumName, forKey: "forumName")
dictionary.setObject(NSNumber(integer: typeid), forKey: "typeid")
dictionary.setObject(NSNumber(integer: page), forKey: "page")
if totalPageNumber != nil {
dictionary.setObject(NSNumber(integer: totalPageNumber!), forKey: "totalPageNumber")
}
let threadDataList: [NSData] = threadList.map { $0.encode() }
dictionary.setObject(threadDataList, forKey: "threadDataList")
return NSKeyedArchiver.archivedDataWithRootObject(dictionary)
}
}
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