runat="server" div causes System.Web.HttpException when accessed from control collection

Question

I have a div that is runat="server". The div is contained in a panel, and within the div are some controls. All of the controls outside of the div (but within the panel) are cleared when I run my "ClearControlsInPanel()" method, which looks like this:

public static void ClearControlsInPanel(Panel paneltoclear, string[] ignorelist)
{
    foreach (Control c1 in paneltoclear.Controls)
    {
        if (c1 is TextBox)
        {
            if (!ignorelist.Contains(c1.ID.ToString()))
            {
                ((TextBox)c1).Text = "";
            }
        }
        if (c1 is DropDownList)
        {
            if (!ignorelist.Contains(c1.ID.ToString()))
            {
                ((DropDownList)c1).SelectedIndex = 0;
            }
        }
        //etc.
    }
}

Once the div is reached, I cannot see the controls in it, and thus none of those controls get cleared. Ironically I found a guy who made a post about the exact same thing, Why adding runat=server to a div tag throws an exception of type 'System.Web.HttpException in controls collection? But the thread ends, with no real solution or explanation.

The full exception is:

base {System.Web.UI.HtmlControls.HtmlContainerControl} = {InnerText = 
'((System.Web.UI.HtmlControls.HtmlContainerControl)
(((System.Web.UI.HtmlControls.HtmlGenericControl)(paneltoclear.Controls._controls
[165])))).InnerText' threw an exception of type 'System.Web.HttpException'}

Please assume that this must remain a runat server div, and cannot be changed to a panel. (I'm almost certain changing it to a panel will solve it, but we have other requirements that need this to be a runat server div (long story)).

Answer 1

Easier if you post the actual code that accesses the div. i.e. which branch of the if statement actually deals with the generic control case. I'm guessing the problem is that you are trying to set the innertext property of the div (as the exception suggests). The trick might be that if the div control has children, then the innertext property doesn't exist, and any text is represented as a literal in the controls array of the div control?

So to clear the child collection try something like... Also probs better if you do else if vs if

    public static void ClearControlsInPanel(ControlCollection controls, string[] ignorelist)
    {
        foreach (Control c1 in controls)
        {
            if (c1 is TextBox)
            {
                if (!ignorelist.Contains(c1.ID.ToString()))
                {
                    ((TextBox)c1).Text = "";
                }
            }
            else if (c1 is DropDownList)
            {
                if (!ignorelist.Contains(c1.ID.ToString()))
                {
                    ((DropDownList)c1).SelectedIndex = 0;
                }
            }
            else
            {
                if (c1.HasControls())
                {
                    ClearControlsInPanel(c1.Controls, ignorelist);
                }
            }
        }
    }

Answer 2

A panel is rendered into a div anyway, so why the div? I see no requirement for it and it solves this issue rather quickly :)