I want to override DetailsView.But I'm failing!?

Question

Hello everybody,

There is my RenderContents() and OnModeChanging() methods. On mode changing method is not working because the DataSource is null.
How can I figure this out?

protected override void RenderContents(HtmlTextWriter output)
{
    base.RenderContents(output);
    output.Dispose();
}

protected override void OnModeChanging(DetailsViewModeEventArgs e)//Mode Changing
{
    ChangeMode(e.NewMode);
    try
    {
        DataBind();
    }
    catch (Exception)
    {

    }
    base.OnModeChanging(e);
}