// UI页面基类
    public class PageBase : System.Web.UI.Page
    {
        //获得应用程序路径
        public string ApplicationPath
        {
            get { return Request.ApplicationPath; }
        }

    }

    //应用页
    public class AppPage:PageBase
    {
        。。。。。引用UserControl
    }    

    //WEB用户控件，在用户控件里引用Pagebase中的ApplicationPath属性
    public partial class UserControl1 : System.Web.UI.UserControl
    {
        //PageLoad
        protected void Page_Load(object sender, EventArgs e)
        {
            if (this.Page != null)
            {
                //获得对PageBase页的引用
                PageBase pagebase = this.Page as PageBase;

                //引用Pagebase页的ApplicationPath属性
                pagebase.ApplicationPath;
            }
        }

    }