userdefaults用法问题swift 3

Question

我刚开始学习Swift，所以这个问题的级别可能对你来说足够明显，但是，我根本无法理解该怎么做。

我“创建”了一个简单的应用程序，允许您添加日期的日志。每个单元格存储您添加的时间，根据时间改变的自定义图标以及日志文本本身（简单文本）。

一切工作正常。但是，因为我不知道“Userdefaults”的内容，所以每当我杀死该应用程序时，时钟就会重置。

我读了很多关于Userdefaults的文章，但我不知道如何保存我的数据，即使我杀了应用程序。

这里就是我试图做的：

class ToDoItem: NSObject, NSCoding { 


var title: String 
var date: String 
var type: String! 

public init(title: String, date: String, type: String) { 

    self.title = title 
    self.date = date 
    self.type = type 

} 

required init?(coder aDecoder: NSCoder) 
{ 
    // Try to unserialize the "title" variable 
    if let title = aDecoder.decodeObject(forKey: "title") as? String 
    { 
     self.title = title 
     let dateFormatter = DateFormatter() 
     dateFormatter.dateStyle = .none 
     dateFormatter.timeStyle = .short 
     self.date = dateFormatter.string(from: Date()) 

     let hour = NSCalendar.current.component(.hour, from: Date()) 
     var tempType = "" 
     switch hour { 
     case 5..<9: tempType = "morning_1" 
     case 6..<12: tempType = "morning_2" 
     case 12: tempType = "noon_1" 
     case 13..<16: tempType = "afternoon_1" 
     case 16..<20: tempType = "dusk_1" 
     case 20..<23: tempType = "evening_1" 
     case 23..<00: tempType = "midnight_1" 
     default: tempType = "morning_1" 


     } 

     self.type = tempType 

    } 



    else 
    { 
     // There were no objects encoded with the key "title", 
     // so that's an error. 
     return nil 
    } 

    let userDefaults = UserDefaults.standard 
    userDefaults.set(true, forKey: "title") 

} 

func encode(with aCoder: NSCoder) 
{ 
    // Store the objects into the coder object 
    aCoder.encode(self.title, forKey: "title") 

    let defaults = UserDefaults.standard 
    defaults.set(false, forKey: "title") 


} 

}

extension Collection where Iterator.Element == ToDoItem 
{ 
    // Builds the persistence URL. This is a location inside 
    // the "Application Support" directory for the App. 
    private static func persistencePath() -> URL? 
    { 
     let url = try? FileManager.default.url(
      for: .applicationSupportDirectory, 
      in: .userDomainMask, 
      appropriateFor: nil, 
      create: true) 

     return url?.appendingPathComponent("todoitems.bin") 
    } 

    // Write the array to persistence 
    func writeToPersistence() throws 
    { 
     if let url = Self.persistencePath(), let array = self as? NSArray 
     { 
      let data = NSKeyedArchiver.archivedData(withRootObject: array) 
      try data.write(to: url) 
     } 
     else 
     { 
      throw NSError(domain: "com.example.MyToDo", code: 10, userInfo: nil) 
     } 
    } 

    // Read the array from persistence 
    static func readFromPersistence() throws -> [ToDoItem] 
    { 
     if let url = persistencePath(), let data = (try Data(contentsOf: url) as Data?) 
     { 
      if let array = NSKeyedUnarchiver.unarchiveObject(with: data) as? [ToDoItem] 
      { 
       return array 
      } 
      else 
      { 
       throw NSError(domain: "com.example.MyToDo", code: 11, userInfo: nil) 
      } 
     } 
     else 
     { 
      throw NSError(domain: "com.example.MyToDo", code: 12, userInfo: nil) 
     } 
    } 
} 

谁能帮助我，或至少点什么，我有什么关系？谢谢！

Answer 1

您使用的是NSKeyedArchiver和NSKeyedUnarchiver，这是与UserDefaults不同的机制。两者都是完全有效的，但你必须选择一个，但它们不能一起工作。

在这里，您正在对ToDoItem的数组进行归档和解除归档。对于这项工作，ToDoItem需要被存档，这意味着它必须实现NSCoding协议，它是：

public protocol NSCoding { 
    public func encode(with aCoder: NSCoder) 
    public init?(coder aDecoder: NSCoder) // NS_DESIGNATED_INITIALIZER 
} 

所有你想要保存的属性必须添加到/从NSCoder对象提取。这里是一个例子：

class ToDoItem: NSObject, NSCoding 
{ 
    var title: String 
    var date: Date 

    required init?(coder aDecoder: NSCoder) 
    { 
     guard let title = aDecoder.decodeObject(forKey: "title") as? String else { 
      return nil 
     } 
     guard let date = aDecoder.decodeObject(forKey: "date") as? Date else { 
      return nil 
     } 
     self.title = title 
     self.date = date 
    } 

    func encode(with aCoder: NSCoder) 
    { 
     aCoder.encode(self.title, forKey: "title") 
     aCoder.encode(self.date, forKey: "date") 
    } 
}