Controls.Add 从列表中删除以前的项目

问：

我正在尝试在我的控制器中创建一个动态菜单，然后我将其呈现到我的视图中。我发现 Controls.Add 正在从我的列表中删除项目，我最终只显示最终项目。如何确保它显示列表中的所有项目，以及如何完成子元素的显示，因为我正在创建动态菜单？

public string CreateDynamicMenu()   
        {
            HtmlGenericControl navbar = new HtmlGenericControl("nav");
            navbar.Attributes.Add("class", "navbar navbar-default");
            HtmlGenericControl containerDiv = new HtmlGenericControl("div");
            containerDiv.Attributes.Add("class", "container-fluid");
            HtmlGenericControl collapseDiv = new HtmlGenericControl("div");
            collapseDiv.Attributes.Add("class", "collapse navbar-collapse");
            HtmlGenericControl navUl = new HtmlGenericControl("ul");
            navUl.Attributes.Add("class", "nav navbar-nav");
            HtmlGenericControl dropdownLi = new HtmlGenericControl("li");
            dropdownLi.Attributes.Add("class", "dropdown");
            HtmlGenericControl mainMenuA = new HtmlGenericControl("a");


            var myMenu = menuListForUserG.GetMenus(Global.CurrentProfile.UserID).OrderBy(x => x.MenuOrder).ThenBy(y => y.MenuName);
            var navbarmenu = myMenu.Where(x => x.ParentID == null);

            foreach (var item in navbarmenu)
            {    
                mainMenuA.InnerText = item.MenuName;
                dropdownLi.Controls.Add(mainMenuA);
                navUl.Controls.Add(dropdownLi);                    
            }  

            collapseDiv.Controls.Add(navUl);
            containerDiv.Controls.Add(collapseDiv);
            navbar.Controls.Add(containerDiv);    

            StringBuilder htmlStringBuilder = new StringBuilder();
            HtmlTextWriter htmlStringWriter = new HtmlTextWriter(new StringWriter(htmlStringBuilder));
            navbar.RenderControl(htmlStringWriter);
            String output = htmlStringBuilder.ToString();
            return output; }