Swift：Error - 条件绑定的初始化程序必须具有可选类型，而不是'Void'（aka'（）'）

Question

使用Swift 3，使用JSON和PHP从MYSQL数据库读取博客阅读器应用程序。用户可以使用关注按钮（以及取消关注按钮）来保存他们希望获得更新的博客。而不是保存整个数组，只是试图保存后面的博客ID，以便应用程序只查找博客ID并显示用户所关注的特定博客。

这是加载用户默认

初始值设定条件绑定时必须有可选的类型，而不是“无效”我得到（又名“（）”）

此错误错误发生在func loadUserDefaults(),MainController.swift第一行if let data = UserDefaults.。 用户点击后续按钮后，我移动单元阵列之间，部分之间在tableview中，然后我请saveUserDefaults()

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 *** ERROR IS HERE *** 
func loadUserDefaults() { 

    // Unarchiving Data -- ERROR: THIS FIRST LINE -- 
    if let data = UserDefaults.standard.setValue(Array(self.followedIdentifiers), forKey: "followedID"), 

     let myFollowedList = NSKeyedUnarchiver.unarchiveObject(with: data) as? [Blog] { 

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

    } 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它处理所有博客的对象和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

的代码行：

let data = UserDefaults.standard.setValue(Array(self.followedIdentifiers), forKey: "followedID") 

没有意义，因为setValue方法不返回任何值。 看起来你需要使用（SWIFT 3）来替代它：

let data = UserDefaults.standard.data(forKey: "followedID") 

更新与@closetCoder评论

Answer 2

执行setValue函数是一个空函数，因此它不能被分配到可变数据因为它没有回报价值。

下面是来自苹果UserDefaults的文档：https://developer.apple.com/documentation/foundation/userdefaults