Windows Phone 中的内容 Web 服务调用未刷新

目前，我正在开发一个 Windows Phone 8.0 应用程序，可在地图上显示大约 100 个 GPS 位置.GPS 数据是通过调用 RESTful webservice 获取的，如下所示:

Currently, I'm developing a Windows Phone 8.0 application that displays some 100 GPS locations on a map. The GPS data is obtained by calling a RESTful webservice as follows:

public async Task<string> GetWebContent(string uri)
{
   string result = null;
   using (var client = new HttpClient())
   {
      result = await client.GetStringAsync(new Uri(uri));        
   }

   return result;
}

这里，HttpClient 取自 Nuget 包Microsoft HTTP 客户端库".

Here, the HttpClient is taken from the Nuget Package "Microsoft HTTP Client Libraries".

第一次调用代码时，会获得数据，并且 GPS 位置很好地绘制在地图上.但是，由于 GPS 设备不断移动，我必须每 30 秒刷新一次数据.这是我撞墙的地方；变量result"中包含的数据永远不会改变.即使几分钟后，数据还是一样的.原始数据包含一个 datetime 属性，它清楚地告诉我数据是旧的，而不仅仅是静止不动的 GPS 设备.如果我将 uri 粘贴到网络浏览器中，并每 15 秒点击一次刷新按钮，数据确实会发生变化，因此网络服务可以正常工作.

The first time the code is called, data is obtained and the GPS locations are nicely plotted on a map. However, since the GPS devices move constantly, I have to refresh the data every 30 seconds. This is where I hit the wall; the data contained in the variable "result" never changes. Even after several minutes the data is the same. The raw data contain a datetime property, which clearly tells me that the data is old and not just the GPS devices standing still. If I paste the uri into a webbrowser, and hit the refresh butten every 15 sec, the data does changed hence the webservice is working properly.

由于 HttpClient 包含在 using 语句中，因此每次都将其丢弃，并且某些隐藏的缓存机制似乎是不可能的.那么，有人有想法吗?

Since the HttpClient is contained in a using-statement, it is disposed off every time and some hidden caching mechanism seems impossible. So, does anyone have an idea?

干杯

更新

我尝试使用 Fiddler，但必须遵循冗长​​的说明才能使其与模拟器连接.完成后，什么都没有了:-s 恢复 Fiddler 安装的所有证书并将代码复制到常规 WPF 应用程序，它在那里工作也是一个魅力.我没有更深入地了解正在发生的事情，但问题似乎与它是一个 Windows 手机项目有关.

I tried using Fiddler, but had to follow a lengthy instruction to make it connect with the emulator. Once done, nothing worked anymore :-s Reverting all the certificates that Fiddler installed and copied the code to a regular WPF application and there it works als a charm.I'm no closer to an understanding of what's going on, but the problem seems to be related to the fact that it's a windows phone project.