本文介绍的菜单控件采用的css 和ul list来显示菜单，生成的html小，无需javascript支持，对大部分的浏览器都支持，除ie6要单独修改css也可以使其支持。
通过本文可以了解asp.net 控件的开发，及Composite设计模式的实际运用。
采用Composite设计模式设计菜单类：
MenuCompositeitem类
复制代码 代码如下:
namespace Ruinet.Controls
{
[Serializable()]
public class MenuCompositeItem
{
private List<MenuCompositeItem> _children = new List<MenuCompositeItem>();
private string _text;
private string _link;
private string _target;
/// <summary>
/// 菜单项
/// </summary>
/// <param name="text">菜单名</param>
/// <param name="link">链接</param>
public MenuCompositeItem(string text, string link)
{
this._text = text;
this._link = link;
}
/// <summary>
/// 菜单项
/// </summary>
/// <param name="text">菜单名</param>
/// <param name="link">链接</param>
/// <param name="target">跳转目标</param>
public MenuCompositeItem(string text, string link, string target)
{
this._text = text;
this._link = link;
this._target = target;
}
/// <summary>
/// 设置或获取菜单名
/// </summary>
public string Text
{
get { return _text; }
set { _text = value; }
}
/// <summary>
/// 设置或获取链接
/// </summary>
public string Link
{
get { return _link; }
set { _link = value; }
}
/// <summary>
/// 跳转目标
/// </summary>
public string Target
{
get { return _target; }
set { _target=value; }
}
/// <summary>
/// 设置或获取子菜单
/// </summary>
public List<MenuCompositeItem> Children
{
get { return _children; }
set { _children = value; }
}
}

MenuComposite类
复制代码 代码如下:
namespace Ruinet.Controls
{
[DefaultProperty("Menu")]
[ToolboxData("<{0}:MenuComposite runat=server></{0}:MenuComposite>")]
public class MenuComposite : WebControl
{
/// <summary>
/// 设置获取选择的菜单
/// </summary>
[Bindable(true)]
[DefaultValue("")]
[Localizable(true)]
public string SelectedMenuText
{
get
{
String s = (String)ViewState["SelectedMenuText"];
return ((s == null) ? String.Empty : s);
}
set
{
ViewState["SelectedMenuText"] = value;
}
}
/// <summary>
/// 获取和设置菜单项从ViewState
/// </summary>
[Bindable(true)]
[DefaultValue(null)]
[Localizable(true)]
public MenuCompositeItem MenuItems
{
get
{
return ViewState["MenuItems"] as MenuCompositeItem;
}
set
{
ViewState["MenuItems"] = value;
}
}
/// <summary>
/// 呈现菜单结构
/// </summary>
/// <param name="output">HTML输出流</param>
protected override void RenderContents(HtmlTextWriter output)
{
MenuCompositeItem root = this.MenuItems;
output.Write(@"<div class=""navmenu"">");
output.Write(@" <ul>");
for (int i = 0; i < root.Children.Count; i++)
{
RecursiveRender(output, root.Children[i]);
}
output.Write(@" </ul>");
output.Write(@"</div>");
}
/// <summary>
/// 递归输出菜单项
/// </summary>
/// <param name="output">HTML输出流</param>
/// <param name="item">菜单项.</param>
/// <param name="depth">Indentation depth.</param>
private void RecursiveRender(HtmlTextWriter output, MenuCompositeItem item)
{
output.Write("<li>");
if (string.IsNullOrEmpty(item.Target))//为空不设置跳转目标
{
output.Write(@"<a href=""" + item.Link + @""">");
}
else
{
output.Write(@"<a href=""" + item.Link + @""" target= """ + item.Target + @""">");
}
if (item.Text == SelectedMenuText) //选中的菜单
{
output.Write(@"<span class=""selected"">");
output.WriteLine(item.Text);
output.WriteLine("</span>");
}
else
{
output.Write(item.Text);
}
output.Write("</a>");
if (item.Children.Count > 0)
{
output.WriteLine();
output.Write("<ul>");
for (int i = 0; i < item.Children.Count; i++)
{
RecursiveRender(output, item.Children[i]);
}
output.Write("</ul>");
}
output.Write("</li>");
}
}
}

在页面中使用
添加对控件的引用后就可以直接在“工具箱”-》Controls组件中 看到MenuComposite组件
再就可以像其他asp.net 控件一样使用
使用：
复制代码 代码如下:
MenuCompositeItem root = new MenuCompositeItem("root", null);
MenuCompositeItem menu01 = new MenuCompositeItem("menu01", ResolveUrl("~/Default.aspx"));
MenuCompositeItem menu02 = new MenuCompositeItem("menu02", ResolveUrl("~/Default.aspx"));
MenuCompositeItem menu03 = new MenuCompositeItem("menu03", ResolveUrl("~/Default.aspx"));
MenuCompositeItem menu04 = new MenuCompositeItem("menu04", ResolveUrl("~/Page04.aspx"));
MenuCompositeItem menu05 = new MenuCompositeItem("menu05", ResolveUrl("~/Default.aspx"));
MenuCompositeItem menu01_01 = new MenuCompositeItem("menu01-01", ResolveUrl("~/Default.aspx"));
MenuCompositeItem menu01_02 = new MenuCompositeItem("menu01-02", ResolveUrl("~/Page01-02.aspx"));
MenuCompositeItem menu01_03 = new MenuCompositeItem("menu01-03", ResolveUrl("~/Default.aspx"));
MenuCompositeItem menu01_04 = new MenuCompositeItem("menu01-04", ResolveUrl("~/Default.aspx"));
menu01.Children.Add(menu01_01);
menu01.Children.Add(menu01_02);
menu01.Children.Add(menu01_03);
menu01.Children.Add(menu01_04);

MenuCompositeItem menu02_01 = new MenuCompositeItem("menu02-01", ResolveUrl("~/Default.aspx"));
MenuCompositeItem menu02_02 = new MenuCompositeItem("menu02-02", ResolveUrl("~/Default.aspx"), "menu02-02");
menu02.Children.Add(menu02_01);
menu02.Children.Add(menu02_02);

MenuCompositeItem menu04_01 = new MenuCompositeItem("menu04-01", ResolveUrl("~/Default.aspx"));
MenuCompositeItem menu04_02 = new MenuCompositeItem("menu04-02", ResolveUrl("~/Page04-02.aspx"), "_blank");
menu04.Children.Add(menu04_01);
menu04.Children.Add(menu04_02);
root.Children.Add(menu01);
root.Children.Add(menu02);
root.Children.Add(menu03);
root.Children.Add(menu04);
root.Children.Add(menu05);

TheMenuComposite.MenuItems = root;
此时生成的编译运行后会生成一个没有样式Ul list ,效果如下：
  
因此要生成可显示和隐藏的菜单项，关键在css的设置上，开始时将二级子菜单设置为隐藏visibility: hidden;
同时定义li的hover事件，li:hover时：自菜单的 visibility要改为visible; 大致原理是这样，当然还有注意菜单项的位置
一级菜单float:left;使其能水平显示。
CSS定义如下：
复制代码 代码如下:
.navmenu *
{
margin: 0;
padding: 0;
}
.navmenu
{
border: #000 1px solid;
height: 25px;
}
.navmenu li
{
/*水平菜单*/
float: left;
list-style: none;
position: relative;
}
.navmenu a
{
display: block;
font-size: 12px;
height: 24px;
width: 100px;
line-height: 24px;
background-color: #CDEB8B;
color: #0000ff;
text-decoration: none;
text-align: center;
border-left: #36393D 1px inset;
border-right: #36393D 1px inset;
border-bottom: #36393D 1px inset;
}
/*单独设置一级菜单样式*/
.navmenu > ul > li > a
{
font-size: 11px;
font-weight: bold;
}
.navmenu a:hover
{
background: #369;
color: #fff;
}
/*新增的二级菜单部分*/
.navmenu ul ul
{
visibility: hidden; /*开始时是隐藏的*/
position: absolute;
left: 0px;
top: 24px;
}
.navmenu ul li:hover ul, .navmenu ul a:hover ul
{
visibility: visible;
}
.navmenu ul ul li
{
clear: both; /*垂直显示*/
text-align: left;
}
/*选中菜单项*/
.navmenu .selected
{
padding-left:15px;
background-position-x:0px;
background-image: url(./res/selected.gif);
background-repeat: no-repeat;
text-decoration:underline;
}

定义CSS后的效果如下：

到此菜单控件已完成。已测试过可以在IE7,IE8,Chrome,Firefox中正常显示，在IE6显示可能会有问题，可以参考纯CSS多级菜单 进行修改，

本文的CSS显示部分参考了此文的介绍。

附上完整代码，如需要可自行下载修改 下载文件