AjaxControlToolkit.Accordion.OnPreRender C# (CSharp) Method

        protected override void OnPreRender(EventArgs e)
        {
            EnsureDataBound();
            base.OnPreRender(e);

            // Set the overflow to hidden to prevent any growth from
            // showing initially before it is hidden by the script if
            // we are controlling the height
            if(AutoSize != AutoSize.None) {
                Style[HtmlTextWriterStyle.Overflow] = "hidden";
                Style[HtmlTextWriterStyle.OverflowX] = "auto";
            }

            // Apply the standard header/content styles, but allow the
            // pane's styles to take precedent
            foreach(var pane in Panes) {
                if(pane.HeaderCssClass == HeaderSelectedCssClass)
                    pane.HeaderCssClass = String.Empty;
                if(!String.IsNullOrEmpty(HeaderCssClass) && String.IsNullOrEmpty(pane.HeaderCssClass))
                    pane.HeaderCssClass = HeaderCssClass;
                if(!String.IsNullOrEmpty(ContentCssClass) && String.IsNullOrEmpty(pane.ContentCssClass))
                    pane.ContentCssClass = ContentCssClass;
            }

            // Get the index of the selected pane, or use the first pane if we don't
            // have a valid index and require one.  (Note: We don't reset the SelectedIndex
            // property because it may refer to a pane that will be added dynamically on the
            // client.  If we need to start with a pane visible, then we'll open the first
            // pane because that's the default value used on the client as the SelectedIndex
            // in this scenario.)
            var index = AccordionExtender.SelectedIndex;
            index = ((index < 0 || index >= Panes.Count) && AccordionExtender.RequireOpenedPane) ? 0 : index;

            // Make sure the selected pane is displayed
            if(index >= 0 && index < Panes.Count) {
                var content = Panes[index].ContentContainer;
                if(content != null)
                    content.Collapsed = false;
            }
        }