asp.net wap 2.0 实现 ishtml32 下 加载 css文件

使用asp.net 开发wap 网站，在ishtml32下，如果手机浏览器支持ishtml32,但是 SupportsCss=False 时，想加载css文件时，采用重写mobile:form的方法来实现
using System;
using System.Configuration;
using System.Web.UI.MobileControls;
using System.Web.UI.MobileControls.Adapters;
public class MyForm : Form
{
     public string CssPath
    {
        get
        {
            if( ViewState["CssPath"] != null)
                return (string)ViewState["CssPath"];
            else
                return string.Empty;
        }
        set
        {
             ViewState["CssPath"] = value;
        }
    }
}
//Now Create the Form Adapter
public class HtmlMyFormAdapter : HtmlFormAdapter
{
    protected new MyForm Control
    {
        get
        {
             return (MyForm)base.Control;
         }
    }
    protected override bool RenderExtraHeadElements( HtmlMobileTextWriter writer )
    {
        if( writer != null )
        {
             if( this.Control.CssPath.Length > 0 )
  &n