Swift：未知错误 - 在展开可选值时意外发现 nil

Question

我知道这是人们在这里发布的常见错误，但我找不到与我正在做的事情相匹配的帖子，即使它基本相同。我是 Swift 新手，只是想找到自己的方法，谢谢。

我第一次打开我的应用程序时，一个从 MYSQL 数据库读取的博客阅读器应用程序，它按预期工作，我可以关注我选择的博客并取消关注。当我关注博客/单元格时，它使用 KeyArchiver 保存到用户默认值，但是当我双击主页按钮从内存中清除应用程序并重新打开应用程序时，它崩溃了。

我的loadUserDefaults 出了点问题，因为我设置了断点，它在self.followedIdentifiers = Set(UserDefaults.standard.stringArray(forKey: "followedID")!) 这一行崩溃了

我知道我有一个可选的，但是如果我用saveUserDefaults 保存它，为什么它会崩溃/返回为零。不是省钱吗？还是我没有正确加载它？

错误是这样的

致命错误：在展开可选值时意外发现 nil

代码：这是MainController.swift

var mainArray = [Blog]()
var followedArray = [Blog]()
var filteredArray = [Blog]()
var followedIdentifiers = Set<String>()

override func viewDidLoad() {
    super.viewDidLoad()

    // Receiving Data from Server
    retrieveDataFromServer()

    // NSCoding - Unarchiving Data (followedID)
    loadUserDefaults()
}

// NSCoding: Archiving UserDefaults
func saveUserDefaults() {

    // Saving to UserDefaults
    let encodedData = NSKeyedArchiver.archivedData(withRootObject: self.followedIdentifiers)
    UserDefaults.standard.setValue(encodedData, forKey: "followedID")
    UserDefaults.standard.synchronize()
}

// NSCoding: Unarchiving UserDefaults
func loadUserDefaults() { // --- Crash is Here ---

    // Unarchiving Data
    if let data = UserDefaults.standard.data(forKey: "followedID"), let myFollowedList = NSKeyedUnarchiver.unarchiveObject(with: data) as? Set<String> {

        self.followedIdentifiers = myFollowedList
        self.followedIdentifiers = Set(UserDefaults.standard.stringArray(forKey: "followedID")!) // CRASH

    } else {
        print("Error/ Empty: (Loading UserDefaults (followedID))")
    }
}

// Retrieving Data from Server
func retrieveDataFromServer() {

    let getDataURL = "http://example.com/receiving.php"
    let url: NSURL = NSURL(string: getDataURL)!

    do {
        let data: Data = try Data(contentsOf: url as URL)
        let jsonArray = try JSONSerialization.jsonObject(with: data, options: .mutableContainers) as! NSMutableArray

        // Clear the arrays
        self.followedArray = [Blog]()
        self.mainArray = [Blog]()

        // Looping through jsonArray
        for jsonObject in jsonArray {

            if let blog = Blog(jsonObject:jsonObject as! [String : Any]) {

                // Check if identifiers match
                if followedIdentifiers.contains(blog.blogID) {
                    self.followedArray.append(blog)
                } else {
                    self.mainArray.append(blog)
                }
            }
        }
    } catch {
        print("Error: (Retrieving Data)")
    }
    myTableView.reloadData()
}

这是Blog.swift，它处理所有博客对象和 NSCoding

class Blog: NSObject, NSCoding {

var blogName: String
var blogStatus1: String
var blogStatus2: String
var blogURL: String
var blogID: String
var blogType: String
var blogDate: String
var blogPop: String


private init (name: String,status1: String,status2: String,url: String,id: String,type: String,date: String,pop: String) {
    blogName = name
    blogStatus1 = status1
    blogStatus2 = status2
    blogURL = url
    blogID = id
    blogType = type
    blogDate = date
    blogPop = pop
    super.init()
}

convenience init?(jsonObject: [String:Any]) {

    guard let bID = jsonObject["id"] as? String,
        let bName = jsonObject["blogName"] as? String,
        let bStatus1 = jsonObject["blogStatus1"] as? String,
        let bStatus2 = jsonObject["blogStatus2"] as? String,
        let bURL = jsonObject["blogURL"] as? String,
        let bType = jsonObject["blogType"] as? String,
        let bDate = jsonObject["blogDate"] as? String,
        let bPop = jsonObject["blogPop"] as? String

        else {
            print("Error: (Creating Blog Object)")
            return nil
    }

    self.init(name: bName, status1: bStatus1, status2: bStatus2, url: bURL, id: bID, type: bType, date: bDate, pop: bPop)

}

convenience required init?(coder aDecoder: NSCoder) {
    guard let blogName = aDecoder.decodeObject(forKey: "blogName") as? String,
        let blogStatus1 = aDecoder.decodeObject(forKey: "blogStatus1") as? String,
        let blogStatus2 = aDecoder.decodeObject(forKey: "blogStatus2") as? String,
        let blogURL = aDecoder.decodeObject(forKey: "blogURL") as? String,
        let blogID = aDecoder.decodeObject(forKey: "blogID") as? String,
        let blogType = aDecoder.decodeObject(forKey: "blogType") as? String,
        let blogDate = aDecoder.decodeObject(forKey: "blogDate") as? String,
        let blogPop = aDecoder.decodeObject(forKey: "blogPop") as? String else {
            print("Error: (Creating Blog Object)")
            return nil
    }
    self.init(name: blogName, status1: blogStatus1, status2: blogStatus2, url: blogURL, id: blogID, type: blogType, date: blogDate, pop: blogPop)
}

func encode(with aCoder: NSCoder) {
    aCoder.encode(blogName, forKey: "blogName")
    aCoder.encode(blogStatus1, forKey: "blogStatus1")
    aCoder.encode(blogStatus2, forKey: "blogStatus2")
    aCoder.encode(blogURL, forKey: "blogURL")
    aCoder.encode(blogID, forKey: "blogID")
    aCoder.encode(blogType, forKey: "blogType")
    aCoder.encode(blogDate, forKey: "blogDate")
    aCoder.encode(blogPop, forKey: "blogPop")
 }
}

Answer 1

我使用File Manager 来保存我的存档数组，这是最好的选择，非常简单。使用Swift 3。感谢@GuyKogus、@Paulw11 和@MartinR

用来保存我的对象

NSKeyedArchiver.archiveRootObject(myObject, toFile: filePath)

用来加载我的对象

if let myFollowedList = NSKeyedUnarchiver.unarchiveObject(withFile: filePath) as? Set<String> {

    myObject = myFollowedList
}