Question

How can I display the error message to the page that was returned from the BeginAsyncOperation? The page loads gracefully with no data but the user would not know why? I verified that the error was thrown but not handled in the BeginAsyncOperation.

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        AddOnPreRenderCompleteAsync(
            new BeginEventHandler(BeginAsyncOperation),
            new EndEventHandler(EndAsyncOperation)
        );
    }
}

private IAsyncResult BeginAsyncOperation(object sender, EventArgs e, AsyncCallback callback, object state)
{
    var t = new ThreadStart(GetData);
    try
    {
        return t.BeginInvoke(callback, null);
    }
    catch (Exception ex)
    {
        this.lblError.Text = ex.Message; 
        this.pnlError.Visible = true;
    }
    return null;
}

private void EndAsyncOperation(IAsyncResult result)
{
    BindData();
    SetControlStates();
}

private void GetData()
{
    try
    {
        throw new Exception("something broke!");
    }
    catch (Exception ex)
    {
        throw ex;
    }
}

Answer 1

I was over-thinking it.

private IAsyncResult BeginAsyncOperation(object sender, EventArgs e, AsyncCallback callback, object state)
{
    var t = new ThreadStart(GetData);
    return t.BeginInvoke(callback, null);
}

private void GetData()
{
    try
    {
        throw new Exception("something broke!");
    }
    catch (Exception ex)
    {
        this.lblError.Text = ex.Message; 
        this.pnlError.Visible = true;
    }
}