在Swift 3中将NSData转换为NSString？

Question

我有一个返回某些系统值的函数。在Swift 2.2中它工作得很好，但我刚刚升级到Xcode 8和Swift 3，现在它失败了。

func ioPlatExpertDevString(_ property: String) -> String {
    // Start tapping in to the IO Service
    let ioPlatformExpertDevice:io_service_t? = IOServiceGetMatchingService(kIOMasterPortDefault, IOServiceMatching("IOPlatformExpertDevice"))

    var sAnswer = "Not Found"
    let cfAnswer:AnyObject! = IORegistryEntryCreateCFProperty(ioPlatformExpertDevice!, "\(property)" as CFString!, kCFAllocatorDefault, 0).takeRetainedValue()
    if (cfAnswer != nil) {
        let nsAnswer = (cfAnswer as! NSString)
        sAnswer = nsAnswer.uppercased
    }

    // Close the IO Service
    IOObjectRelease(ioPlatformExpertDevice!)

    return sAnswer
}

之前我在用“CFData”而不是“AnyObject”，它可以成功构建，但在运行时出现以下错误:

无法将类型为 '__NSCFData' (0x7fff7b833ec0) 的值转换为类型为 'NSString' (0x7fff7ac32038)。

- PhillyPhoto

---

你正在调用哪个属性的函数？ - Martin R

Answer 1

替换

let nsAnswer = (cfAnswer as! NSString) 

To

let nsAnswer = NSString(data: cfAnswer as! Data, encoding: String.Encoding.utf8.rawValue)

- Leo Valentim

Answer 2

对于更近期的Swift版本：

String(decoding: data, as: UTF8.self)

- kakubei

Answer 3

请不要在编译器没有提示的情况下注释类型。

例如，IOServiceGetMatchingService 返回一个非可选的 io_service_t，你的可选注释会使它更糟糕。 IORegistryEntryCreateCFProperty 返回 Unmanaged<CFTypeRef>!，也不需要注释，以及字符串插值和隐式解包可选项的转换。 CFTypeRef 可以桥接转换为本地 Swift 类型。

如果返回类型是 (NS)Data，那么它在之前的版本中很少能够工作。

此代码考虑了 String 和 Data，如果后者可以转换为 String。

func ioPlatExpertDevString(_ property: String) -> String {
  // Start tapping in to the IO Service
  let ioPlatformExpertDevice = IOServiceGetMatchingService(kIOMasterPortDefault, IOServiceMatching("IOPlatformExpertDevice"))

  var sAnswer = "Not Found"
  let cfAnswer = IORegistryEntryCreateCFProperty(ioPlatformExpertDevice, property as CFString, kCFAllocatorDefault, 0).takeRetainedValue()
  if let cfData = cfAnswer as? Data, let answer = String(data:cfData, encoding:.utf8) {
    sAnswer = answer.uppercased()
  } else if let answer = cfAnswer as? String {
    sAnswer = answer.uppercased()
  }
  // Close the IO Service
  IOObjectRelease(ioPlatformExpertDevice)
  return sAnswer
}

- vadian