Question

I have an ASP.NET page that requires data from another DLL and the process might take a long time. So, I set out to use APM. But when I try that, the page just never stops loading. It loads indefinitely. Is there something I’m doing wrong?

Here is my web page:

List<string> allVoices;
GetAllVoicesDelegate getVoicesDelegate;
internal delegate List<String> GetAllVoicesDelegate();

protected void Page_Load(object sender, EventArgs e)
{
  Page.AddOnPreRenderCompleteAsync(new BeginEventHandler(BeginGetDropDownValues),
       new EndEventHandler(EndGetDropDownValues));
}

public IASyncResult BeginGetDropDownValues(object o,EventArgs args,AsyncCallback cb,object obj)
{
   getVoicesDelegate = MyLib.getStrings;
   return getVoicesDelegate.BeginInvoke(EndGetDropDownValues,null);
}

public void EndGetDropDownValues(IASyncResult ar)
{
   allVoices = getVoicesDelegate.EndInvoke(ar);
}

protected override OnPreRenderComplete(EventArgs e)
{
  if(allVoices.Count>0)
  {
    foreach(String str in allVoices)
    {
       Response.Write(str);
    }
  }
  base.OnPreRenderComplete(e);

}

Here is the MyLib.getStrings() method in another DLL:

public List<String> getStrings()
{
   List<String> allStr=new List<string>();
   allStr.Add("1");
   allStr.Add("2");
   allStr.Add("3");
   allStr.Add("4");
}

Answer 1

If you have to get data from a long running process, making async calls from the web page won’t help you because in the end, the process needs to finish before the page can finish rendering. Making async calls frees you to do other stuff in the mean time, but the page can’t render until all the activity on it is finished.

I think you’ll have to take a different approach, either using Ajax to poll the server until the response is ready, or creating an intermediate page that tells the user to wait until the process is complete. Once it’s complete, the page refreshes and the user sees the data.