用HtmlLink来改变网站的主题

#region Theme
            // 注册样式(将主题样式至于通用样式后面) 
            HtmlLink themeCss = new HtmlLink();
            themeCss.Href = GetThemeUrl();
            themeCss.Attributes["id"] = "commonPageStyle";
            themeCss.Attributes["rel"] = "stylesheet";
            themeCss.Attributes["type"] = "text/css";
            int commonCssIndex = 0;
            bool existsCommonCss = false;

            foreach (Control control in Page.Header.Controls)
            {
                if (control is HtmlLink && (control as HtmlLink).Href.IndexOf("/css/commPage.css", StringComparison.OrdinalIgnoreCase) > -1)
                {
                    Page.Header.Controls.AddAt(commonCssIndex + 1, themeCss);
                    existsCommonCss = true;
                    break;
                }
                commonCssIndex++;
            }
            if (!existsCommonCss)
            {
                Page.Header.Controls.AddAt(0, themeCss);
            }
            #endregion

private string GetThemeUrl()
        {
            string themeStr = "/css/themes/{0}/commPage.css?v=140917";
            switch (UserSession.getInstance().UserTheme)
            {
                case "blue":
                    themeStr = string.Format(themeStr, "blue");
                    break;
                case "purple":
                    themeStr = string.Format(themeStr, "purple");
                    break;
                case "red":
                    themeStr = string.Format(themeStr, "red");
                    break;
                case "green":
                    themeStr = string.Format(themeStr, "green");
                    break;
                default:
                    themeStr = string.Format(themeStr, "default");
                    break;
            }
            return themeStr;
        }