通过Ajax技术对DropDrowList控件联动改变应用

改变一个DropDrowList会引起另一个DropDrowList的值改变：

Page Code：

<table>
            <tr>
                <th>省份</th>
                <td>
                    <asp:DropDownList ID="drpProvice" runat="server" 
                        onselectedindexchanged="drpProvice_SelectedIndexChanged" AutoPostBack="True">
                    </asp:DropDownList>
                </td>
                <th>城市</th>
                <td><asp:DropDownList ID="drpCity" runat="server">
                    </asp:DropDownList></td>
            </tr>
        </table>

protected void Page_Load(object sender,EventArgs e)
        {
			if (!IsPostBack)
			{
				InitData();
			}
        }
		
		protected virtual Int32 StringToInt32(string val,Int32 defaultVal)
		{
			int tmp = 0;
			if (Int32.TryParse(val,out tmp))
			{
				return tmp;
			}
			return defaultVal;
		}
		public sqlConnection Open()
		{
			string strConn = ConfigurationManager.ConnectionStrings["MysqLDataBase"].ConnectionString;
			sqlConnection conn = new sqlConnection(strConn);
			conn.Open();
			return conn;
		}
		public void Close()
		{
			sqlConnection conn = Open();
			conn.Close();
		}
		private void InitData()
		{
			ProviceBind();
			Citybind();
		}
		private void ProviceBind()
		{
			string strsql = "select * from Ajax_Provice";
			sqlConnection conn = Open();
			sqlDataAdapter da = new sqlDataAdapter(strsql,conn);
			DataSet ds = new DataSet();
			da.Fill(ds);
			drpProvice.DataSource = ds.Tables[0];
			drpProvice.DataTextField = "c_provName";
			drpProvice.DataValueField = "c_provId";
			drpProvice.DataBind();
			//drpTypeId.Items.Insert(0,new ListItem("全部",""));

		}
		private void Citybind()
		{
			int temp = StringToInt32(drpProvice.SelectedValue,0);
			string strsql = "select * from Ajax_City Where c_provId = {0}";
			strsql = string.Format(strsql,temp);
			sqlConnection conn = Open();
			sqlDataAdapter da = new sqlDataAdapter(strsql,conn);
			DataSet ds = new DataSet();
			da.Fill(ds);
			drpCity.DataSource = ds.Tables[0];
			drpCity.DataTextField = "c_city";
			drpCity.DataValueField = "c_provId";
			drpCity.DataBind();
			Close();
		}
		protected void drpProvice_SelectedIndexChanged(object sender,EventArgs e)
		{
			Citybind();
		}