检索设备设置后更新UI

Question

我想在Swift中做一些简单的事情。我必须从设备中检索一些设置，然后使用这些设置初始化一些UI控件。可能需要几秒钟才能完成检索，所以我不希望代码在检索(异步)之后才继续。

我已经在许多网站上阅读了无数的帖子，包括这个网站，并阅读了许多教程。似乎没有一个对我有效。

另外，为了便于封装，我希望将详细信息保存在device对象中。

当我运行应用程序时，在我看到来自初始化方法的打印之前，我看到了来自该方法的打印。

// Initializing method

brightnessLevel = 100
device.WhatIsTheBrightnessLevel(level: &brightnessLevel)
print("The brightness level is \(brightnessLevel)")


// method with the data retrieval code

func WhatIsTheBrightnessLevel(level brightness: inout Int) -> CResults
{
var brightness: Int
var characteristic: HMCharacteristic
var name: String
var results: CResults
var timeout: DispatchTime
var timeoutResult: DispatchTimeoutResult



// Refresh the value by querying the lightbulb
name = m_lightBulbName
characteristic = m_brightnessCharacteristic!
brightness = 100
timeout = DispatchTime.now() + .seconds(CLightBulb.READ_VALUE_TIMEOUT)
timeoutResult = .success
results = CResults()
results.SetResult(code: CResults.code.success)
let dispatchGroup = DispatchGroup()
DispatchQueue.global(qos: .userInteractive).async
  {
  //let dispatchGroup = DispatchGroup()
  dispatchGroup.enter()
  characteristic.readValue(completionHandler:
    { (error) in
      if error != nil
        {
        results.SetResult(code: CResults.code.homeKitError)
        results.SetHomeKitDescription(text: error!.localizedDescription)
        print("Error in reading the brightness level for \(name): \(error!.localizedDescription)")
        }
       else
          {
          brightness = characteristic.value as! Int
          print("CLightBulb: -->Read the brightness level.  It is \(brightness) at " + Date().description(with: Locale.current))
          }
      dispatchGroup.leave()
    })
    timeoutResult = dispatchGroup.wait(timeout: timeout)
    if (timeoutResult == .timedOut)
      {
      results.SetResult(code: CResults.code.timedOut)
      }
     else
        {
        print("CLightBulb: (After wait) The brightness level is \(brightness) at " + Date().description(with: Locale.current))
        self.m_brightnessLevel = brightness
        }
  }
return(results)
}



Thank you!

Answer 1

如果你打算用你自己的函数包装一个异步函数，通常最好也给你的包装器函数一个完成处理程序。请注意对完成处理程序的调用。这就是你传递结果值的地方(即在闭包中)：

func getBrightness(characteristic: HMCharacteristic, completion: @escaping (Int?, Error?) -> Void) {

    characteristic.readValue { (error) in

        //Program flows here second

        if error == nil {
            completion(characteristic.value as? Int, nil)
        } else {
            completion(nil, error)
        }
    }

    //Program flows here first
}

然后，当你调用你的函数时，你只需要确保你是在完成处理程序中处理结果(即闭包)：

getBrightness(characteristic: characteristic) { (value, error) in

    //Program flows here second

    if error == nil {
        if let value = value {
            print(value)
        }
    } else {
        print("an error occurred: \(error.debugDescription)")
    }
}

//Program flows here first

请始终记住，在异步函数完成之前，代码将流经。所以你必须组织你的代码，使任何依赖于返回的值或错误的东西在完成之前都不会被执行。