Web Client - Asynchronous operations are not allowed in this context

Question

It is a Class Library and it is getting called form a web page

try
  {
    System.Net.WebClient wc = WebAccess.GetWebClient();
    wc.UploadStringCompleted += new System.Net.UploadStringCompletedEventHandler(wc_UploadStringCompleted);
    wc.UploadStringAsync(new Uri("http://" + MobileWLCUrl + urlCreateCacheAPI), GetJSONforGetMenuDetails(Id, MenuIds));                    
  }
catch (Exception ex) { EngineException.HandleException(ex); }

void wc_UploadStringCompleted(object sender, System.Net.UploadStringCompletedEventArgs e)
    {
        string result = e.Result;
        EngineException.CreateLog("Cache Created (for Menus: " + MenuIds + ") in API for LocationId: " + LocId);
    }

hie guys, m trying to hit this url asynchronously and it is giving me this error, any help will be appriciated.

Asynchronous operations are not allowed in this context. 
Page starting an asynchronous operation has to have the Async attribute set to true 
and an asynchronous operation can only be started on a page prior to PreRenderComplete event. 

at System.Web.AspNetSynchronizationContext.OperationStarted()
at System.Net.WebClient.UploadStringAsync(Uri address, String method, String data, Object userToken)
at System.Net.WebClient.UploadStringAsync(Uri address, String data)

Thnx...

Solution

Add the Async="true" parameter to the @Page directive.

<%@ Page Async="true" ... %>

Siwani,

You need to apply this change in the page (stored in "http://" + MobileWLCUrl + urlCreateCacheAPI) called in following code:

wc.UploadStringAsync(new Uri("http://" + MobileWLCUrl + urlCreateCacheAPI), GetJSONforGetMenuDetails(Id, MenuIds));