C# 从PCL内的异步调用返回值

我有一个非PCL方法，它从RESTful服务获取数据，然后反序列化并返回数据。看起来像这样

    public WeatherData GetWeather
    {
        get
        {
            if (!ftrackData.Online)
                return new WeatherData();

            string param = string.Format("lat={0}&lon={1}&APPID={2}", AppDelegate.Self.Latitude, AppDelegate.Self.Longitude, AppDelegate.Self.WeatherID);
            var request = WebRequest.Create("http://api.openweathermap.org/data/2.5/forecast?" + param) as HttpWebRequest;
            request.Method = "GET";
            request.Accept = "application/json";
            request.ContentType = "application/json";

            string responseContent;
            try
            {
                using (var response = request.GetResponse() as HttpWebResponse)
                {
                    using (var reader = new StreamReader(response.GetResponseStream()))
                    {
                        responseContent = reader.ReadToEnd();
                    }
                }
                var deserial = Deserialize<WeatherData>(responseContent);
                return deserial;
            }
            catch (WebException ex)
            {
                Console.WriteLine("Deserialiser failed : {0}--{1}", ex.StackTrace, ex.Message);
                return null;
            }
        }
    }

但这不会编译，因为并非所有路径都返回值

---

如何才能让报税表在匿名回拨中填写好天气信息后才能返回？

您不使用WebRequest.GetResponseAsync的原因是什么？您能使用.NET Framework 4.5吗？@Nodoid：通常认为在属性getter中执行异步网络调用是一种糟糕的方法。一个更好的方法是异步方法。它很简单——使用一个方法。您共享的代码中会散发出大量的代码气味-属性的代码大小应该更小，并且它不应该触及自己类之外的任何内容，尤其是网络、数据库或其他类似的内容

    public WeatherData GetWeather
    {
        get
        {
            var param = string.Format("lat={0}&lon={1}&APPID={2}", App.Self.Latitude, App.Self.Longitude, App.Self.WeatherID);
            var request = WebRequest.Create("http://api.openweathermap.org/data/2.5/forecast?" + param) as HttpWebRequest;
            request.Method = "GET";
            request.Accept = "application/json";
            request.ContentType = "application/json";

            var Weather = new WeatherData();
            string responseContent;
            try
            {
                var asyncResult = request.BeginGetResponse(new AsyncCallback(s =>
                        {
                            var response = (s.AsyncState as WebRequest).EndGetResponse(s);

                            using (var reader = new StreamReader(response.GetResponseStream()))
                            {
                                responseContent = reader.ReadToEnd();
                            }
                            Weather = Deserialize<WeatherData>(responseContent);
                        }), request);
                return Weather;

            }
            catch (WebException ex)
            {
                Debug.WriteLine("Deserialiser failed : {0}--{1}", ex.StackTrace, ex.Message);
                return Weather;
            }
        }
    }

if (asyncResult.IsCompleted)
   return Weather;