符合NSCoding

Question

我永远也搞不懂为什么我会得到这个类不符合NSCoding协议的错误。也许另一双眼睛会有所帮助。我已经尝试添加注释，以明确每个函数都在做什么。

import Foundation
import UIKit

class Search: NSObject, NSCoding {

// Global Variables
var articlePicture: UIImage!
var articleTitle: String

// MARK: Public Init
init(articlePicture: UIImage, articleTitle: String) {
    self.articlePicture = articlePicture
    self.articleTitle = articleTitle
}

// Required NSCoding Protocol
required convenience init?(coder decoder: NSCoder) {
    guard let articlePicture = decoder.decodeObject(forKey: "articlePicture") as? UIImage,
        let articleTitle = decoder.decodeObject(forKey: "articleTitle") as? String
        else { return nil }

    self.init(
        articlePicture: articlePicture,
        articleTitle: articleTitle
    )
}

// Required NSCoding Protocal
func encodeWithCoder(coder: NSCoder) {
    coder.encode(self.articlePicture, forKey: "articlePicture")
    coder.encode(self.articleTitle, forKey: "articleTitle")
}

// Initialize [Search]
static var searches = [Search]()

static func getSearches() -> [Search]{
    return searches
}

static func setSearch(search: Search){
    searches.append(search)
}

// NSUserDefaults Searches Array funcs
static func saveSearches(){
    let searchData = NSKeyedArchiver.archivedData(withRootObject: searches)
    UserDefaults.standard.set(searchData, forKey: "searches")
}

static func loadSearches() -> [Search]{
    let searchData = UserDefaults.standard.object(forKey: "searches") as? NSData

    if let searchData = searchData {
        searches = (NSKeyedUnarchiver.unarchiveObject(with: searchData as Data) as? [Search])!
        return searches
    }
    return searches
}
}