ios - Swift:函数调用顺序错误？

Question

因此，我一直在使用以下简要数据模型开发天气应用

class CurrentWeather
{
    private var _cityName: String!
    private var _date: String!
    private var _weatherType: String!
    private var _currentTemp: Double!

    var cityName: String
    {
        if _cityName == nil
        {
            _cityName = ""
        }
        return _cityName
    }

    // Same idea for getters var date, var weatherType and
    //  var currentTemp (returns 0.0 if it is nil)
    // Not showing that here 

    func downloadWeatherDetails(completed: DownloadComplete)
    {
    // Function which computes values though a url and stores in instance variables
    // Not showing the entire actual function here
                self._cityName = name.capitalized. // value computed earlier
                print(self._cityName)
                self._weatherType = main.capitalized // value computed earlier
                print(self._weatherType)


                self._currentTemp = currentTemp - 273.15 // value computed earlier
                print(self._currentTemp)

                completed()

     }

}

其中 DownloadComplete 类型是 ()->() 的类型别名

在主 ViewController.swift 中，我创建了一个对象并调用了这个函数(使用尾随闭包语法)

var currentWeather: CurrentWeather!

override func viewDidLoad()
{
    super.viewDidLoad()
    currentWeather = CurrentWeather()
    currentWeather.downloadWeatherDetails {
         self.updateMainUI() // I have created this function
    }
}
func updateMainUI()
{
    dateLabel.text = currentWeather.date
    currentTempLabel.text = String(currentWeather.currentTemp)
    locationLabel.text = currentWeather.cityName
    currentWeatherTypeLabel.text = currentWeather.weatherType
    currentWeatherImage.image = UIImage(named: currentWeather.weatherType)

    print("Tested: \(currentWeather.currentTemp)")
    print("Tested: \(currentWeather.cityName)")
    print("Tested: \(currentWeather.weatherType)")
}

所以预期输出:

逻辑上，

1. 我创建了一个 CurrentWeather 对象

2. 调用了 downloadWeatherDetails 函数，它应该在私有(private)变量中加载不同的计算值。

3. 调用用户定义的 updateMainUI 函数，该函数在我的应用的 UI 上显示不同的值

所以输出应该是这样的

Birim. //cityname

Clear. //weatherType

29.134 //currentTemp

Tested: 29.134

Tested: Birim

Tested: Clear

但我得到的输出是

Tested: 0.0

Tested:             (indicating "")

Tested:             (indicating "")

Birim

Clear

29.134

那么，基本上 downloadWeatherDetails 和 updateMainUI 函数的调用顺序是错误的？为什么会这样？这在某种程度上与函数的异步执行有关吗？

我试过不使用尾随闭包，但还是不行。

我还尝试将闭包留空并在 downloadWeatherDetails 调用之后调用 updateMainUI ，如下所示

currentWeather.downloadWeatherDetails {

}
self.updateMainUI() 

但这也行不通。为什么以错误的顺序调用函数有任何想法吗？

更新:

下划线变量是私有(private)变量而非下划线变量是getters like

    var cityName: String
    {
        if _cityName == nil
        {
            _cityName = ""
        }
       return _cityName
    } 

     // Same idea for getters var date, var weatherType and
     //  var currentTemp (returns 0.0 if it is nil)
     // Not showing that here

更新 2:

项目文件在这里(以备不时之需):https://github.com/danny311296/Weather-App

Answer 1

您必须在 Alamofire 请求回调中调用“completed()”函数。由于请求函数是异步的，因此在执行 completed() 之前不会等待它完成。

Alamofire.request(CURRENT_WEATHER_URL).responseJSON { response in

    // handle response...

    // when done call completed
    completed()
}