Issue with HttpClient.GetStringAsync method in windows phone 8.1 - windows

Question

private async void refresh_Tapped(object sender, TappedRoutedEventArgs e)
{
httpclient.CancelPendingRequests();
string url = "http://gensav.altervista.org/";
var source = await httpclient.GetStringAsync(url); //PROBLEM
source = WebUtility.HtmlDecode(source);
HtmlDocument result = new HtmlDocument();
result.LoadHtml(source);
List<HtmlNode> toftitle = result.DocumentNode.Descendants().Where
(x => (x.Attributes["style"] != null
&& x.Attributes["style"].Value.Contains("font-size:14px;line-height:20px;margin-bottom:10px;"))).ToList();
var li = toftitle[0].InnerHtml.Replace("<br>", "\n");
li = li.Replace("<span style=\"text-transform: uppercase\">", "");
li = li.Replace("</span>", "");
postTextBlock.Text = li;
}
What this code does is basically retrieve a string from a website (HTML source which is parsed right after). This code is executed whenever i click a button: the first time i click it it works correctly, but the second time i think that the method (GetStringAsync) returns an uncompleted task and then execution continues using the old value of source. Indeed, my TextBlock does not update.
Any solution?

Answer 1

You get probably a cached response.
May this will work for you:
httpclient.CancelPendingRequests();
// disable caching
httpclient.DefaultRequestHeaders.Add("Cache-Control", "no-cache");
string url = "http://gensav.altervista.org/";
var source = await httpclient.GetStringAsync(url);
...
You can also add a meaningless value to your url like this:
string url = "http://gensav.altervista.org/" + "?nocahce=" + Guid.NewGuid();

Answer 2

To prevent Http responses from getting cached, I do this (in WP8.1):
HttpBaseProtocolFilter filter = new HttpBaseProtocolFilter();
filter.CacheControl.ReadBehavior =
Windows.Web.Http.Filters.HttpCacheReadBehavior.MostRecent;
filter.CacheControl.WriteBehavior =
Windows.Web.Http.Filters.HttpCacheWriteBehavior.NoCache;
_httpClient = new HttpClient(filter);
Initialize your HttpClient in this manner to prevent caching behaviour.