无法解码Swift中保存的信息

Question

我试图在swift中使用NSKeyedArchiver保存一个非常简单的对象，我看到它正在使用值正确保存，但每当它尝试解码保存的数据时它就会失败。我是swift的新手，我尝试过googling和os_log（ing）所有内容，但我看不出问题出在哪里。这是我想要保存的对象......

class TrackedAmount: NSObject, NSCoding {
  var cups: Int
  var fraction: Float?

  struct PropertyKey {
    static let cups = "cups"
    static let fraction = "fraction"
  }
  init?(cups: Int, fraction: Float?) {
    os_log("Running init? function", log: .default, type: .debug)
    if(cups < 0) {
      os_log("Cups less than 0. Returning nil", log: .default, type: .debug)
      return nil
    }
    self.cups = cups
    self.fraction = fraction
  }

  required convenience init? coder aDecoder: NSCoder) {
    os_log("Running required convenience init? function", log: .default, type: .debug)
    guard let cups = aDecoder.decodeObject(forKey: PropertyKey.cups) as? Int else {
      os_log("Unable to decode cups", log: .default, type: .debug)
      return nil
    }
    guard let fraction = aDecoder.decodeObject(forKey: PropertyKey.fraction) as? Float else {
      os_log("Unable to decode fraction", log: .default, type: .debug)
      return nil
    }
    self.init(cups: cups, fraction: fraction)
  }

  func encode(with aCoder: NSCoder) {
    aCoder.encode(cups, forKey: PropertyKey.cups)
    aCoder.encode(fraction, forKey: PropertyKey.fraction)
  }

然后在我的ViewController中，我试图获取并保存它们，...

 private func saveAmount() {
    trackedToday = TrackedAmount(cups: selectedCups, fraction: selectedFraction)
    print("data.... cups: " + String(trackedToday!.cups) + " fractions: " + String(trackedToday!.fraction!))
    let fullPath = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0].appendingPathComponent("dailytracked")
    do {
      let data = try NSKeyedArchiver.archivedData(withRootObject: trackedToday!, requiringSecureCoding: false)
      try data.write(to: fullPath)
    } catch {
      os_log("Unable to save tracking amount", log: .default, type: .debug)
    }
  }

  private func loadDailyTracked() -> TrackedAmount? {
    let fullPath = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)[0].appendingPathComponent("dailytracked")
    if let nsData = NSData(contentsOf: fullPath) {
      do {
        let data = Data(referencing: nsData)
        if let loadedData = try NSKeyedUnarchiver.unarchiveTopLevelObjectWithData(data) as? TrackedAmount {
          os_log("it finally worked", log: .default, type: .debug)
          return loadedData
        }
      } catch {
        os_log("Couldn't read from file", log: .default, type: .debug)
        return nil
      }
    return nil
  }

它正确保存，但每当我尝试运行loadDailyTracked（）方法时，我在xcode的输出部分得到以下内容...

运行所需的便利init？功能

无法解码杯子

我似乎无法弄清楚为什么它不能解码杯子，我知道数据正在保存，因为除了它试图从保存的数据读取时，没有任何日志显示任何故障。我甚至在保存之前记录了信息，它显示的是正确的数据。有人有主意吗？我是IOS和Swift的新手，我无法弄明白这一点。谢谢。

*旁注，如果您需要更多代码或信息，我很乐意提供它，我只是试图保持帖子不要太大，如果它不需要。

Answer 1

在NSCoder方面，像Int和Float这样的标量类型不是对象，专用方法不返回选项

required convenience init? coder aDecoder: NSCoder) {
    os_log("Running required convenience init? function", log: .default, type: .debug)
    let cups = aDecoder.decodeInteger(forKey: PropertyKey.cups)
    let fraction = aDecoder.decodeFloat(forKey: PropertyKey.fraction)
    self.init(cups: cups, fraction: fraction)
}

斯威夫特的NSCoding很重。强烈建议使用Codable协议来序列化结构和类。