asp.net中使用下拉菜单的级联问题

页面文件

<asp:DropDownList ID="DropDownList1" runat="server" OnSelectedIndexChanged="DropDownList1_SelectedIndexChanged" AutoPostBack="True">

          <asp:ListItem>城市1</asp:ListItem>

           <asp:ListItem>城市2</asp:ListItem>

</asp:DropDownList>

<asp:DropDownList ID="DropDownList2" runat="server">

</asp:DropDownList>

程序文件

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)

       {

               if (DropDownList1.SelectedItem.Text == "城市1")

               {  

                     DropDownList2.Items.Clear(); DropDownList2.Items.Add("区1"); DropDownList2.Items.Add("区2");

               }

             else if (DropDownList1.SelectedItem.Text == "城市2")

             {

                      DropDownList2.Items.Clear(); DropDownList2.Items.Add("区3"); DropDownList2.Items.Add("区4");

             }

      }

 注意第一个dropdownlist的AutoPostBack="True"一定要设置 其实如果这种省市区联动的一般不用数据库，直接在js里面写，或者找现成的有很多，
放数据库里浪费服务器资源，而且刷新效果不好。

提供一个比较好的省市三级联动的DropDownList+Ajax的三种框架(aspnet/Jquery/ExtJs)
示例：http://www.cnblogs.com/downmoon/archive/2010/06/15/1758675.html

 

附加一个使用数据库数据的例子：

前台控件代码：

<asp:PlaceHolder ID="PlaceHolder1" runat="server">
    <asp:Label ID="Label1" runat="server" Text="模块："></asp:Label>
       <asp:DropDownList ID="DropDownList1" runat="server"
            onselectedindexchanged="DropDownList1_SelectedIndexChanged" 
    AutoPostBack="True">
        </asp:DropDownList>
        &nbsp;&nbsp;&nbsp;&nbsp;<asp:Label ID="Label2" runat="server" Text="分类：" Visible="false"></asp:Label>
         <asp:DropDownList ID="DropDownList2" Visible="false" runat="server">
        </asp:DropDownList>
</asp:PlaceHolder>

后台代码段：

    protected string SqlModuleList = "";
    protected string SqlTypeList = "";
    SqlHelper sqlhelper = new SqlHelper();
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            ModuleList(); //首次加载模块的下拉数据
        }
    }
    protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
    {
        if (DropDownList1.SelectedItem.Text != "")
        {
            SqlTypeList = "select TypeID,TypeName from KY_SendMessage_Type as T,KY_SendMessage_Module as M 
                            where T.ModuleID=M.ModuleID and T.ModuleID=" + DropDownList1.SelectedValue + "";
            DataSet ds = sqlhelper.readDataSet(SqlTypeList);
            DataTable dt = ds.Tables[0];
            if (dt.Rows.Count != 0)//判断模块下面是否有子分类
            {
                Label2.Visible = true;
                DropDownList2.Visible = true;
                DropDownList2.Items.Clear();
            }
            else
            {
                Label2.Visible = false;
                DropDownList2.Visible = false;
            }
            DropDownList2.DataSource = dt;
            DropDownList2.DataValueField = "TypeID";
            DropDownList2.DataTextField = "TypeName";
            DropDownList2.DataBind();
        }
    }
    protected void ModuleList()
    {
        SqlModuleList = "select * from KY_SendMessage_Module as M";
        DataSet ds = sqlhelper.readDataSet(SqlModuleList);
        DataTable dt = ds.Tables[0];
        DropDownList1.DataSource = dt;
        DropDownList1.DataValueField = "ModuleID";
        DropDownList1.DataTextField = "ModuleName";
        DropDownList1.DataBind();
    }

部分效果图：

                         初始加载图

　　　　　　　点击选项加载子下拉图