dropdownlist代码
<asp:dropdownlist id="ddlWk" Runat="server" AutoPostBack="True" Enabled="False">
               <asp:ListItem Value="0">东京</asp:ListItem>
               <asp:ListItem Value="3">九州</asp:ListItem>
               <asp:ListItem Value="8">北海道</asp:ListItem>
               <asp:ListItem Value="9">四国</asp:ListItem>
              </asp:dropdownlist>

aspx.cs文件代码核心如下：
private void Page_Load(object sender, System.EventArgs e)
  {
   if(!IsPostBack)
   {
       Session["WP"] ="0";
       ddlWk_getS();
       BindGrid();
   } 
  }
  private void ddlWk_getS()
  {
   switch (Session["WP"].ToString())
   {
    case "0":ddlWk.SelectedIndex=0;
     break;
    case "3":ddlWk.SelectedIndex=1;
     break;
    case "8":ddlWk.SelectedIndex=2;
     break;
    case "9":ddlWk.SelectedIndex=3;
     break;
    default:ddlWk.SelectedIndex=0;
     break;
   }
  }
  protected void BindGrid()
  {
   MyDataGrid.DataSource=GetData().Tables["vCO"].DefaultView;
   MyDataGrid.DataBind();
   //COUNT.Text=MyDataGrid.Columns.Count.ToString();
  }

  /// <summary>
  /// 返回Data
  /// </summary>
  ///<returns></returns>
  private DataSet GetData()
  {
   string strConn=(String) ((NameValueCollection) Context.GetConfig("system.web/database"))["strConn"];
   using (SqlConnection conn = new SqlConnection(strConn))
   {
    SqlCommand cmd = new SqlCommand("sp_C",conn);
    cmd.CommandType=CommandType.StoredProcedure;
    cmd.Parameters.Add("@place",SqlDbType.VarChar,2);
    cmd.Parameters["@place"].Value=Session["WP"].ToString();
    conn.Open();

    SqlDataAdapter da = new SqlDataAdapter();
    da.SelectCommand=cmd;
    DataSet ds=new DataSet();
    da.Fill(ds,"vCO");
    Count.Text="ヒット："+ds.Tables["vCO"].Rows.Count.ToString()+"件";
    return ds;
   }

  }
  /// <summary>
  ///从DataSet中除一
  /// </summary>
  /// <param name="sender"></param>
  /// <param name="E"></param>
  protected void MyDataGrid_Delete(Object sender, DataGridCommandEventArgs E)
  {
    String strID=MyDataGrid.DataKeys[(int)E.Item.ItemIndex].ToString();
    //删除操作
  }
  /// <summary>
  /// 分页操作
  /// </summary>
  /// <param name="sender"></param>
  /// <param name="e"></param>
  protected void MyDataGrid_PageIndexChanged(object source, DataGridPageChangedEventArgs e)
  {
   MyDataGrid.CurrentPageIndex=e.NewPageIndex;
   BindGrid();
  }
  /// <summary>
  /// 排序
  /// </summary>
  /// <param name="sender"></param>
  /// <param name="e"></param>
  protected void Sort_Grid(object sender, DataGridSortCommandEventArgs e)
  {
   DataView dv= new DataView(GetData().Tables["vCO"]);
   dv.Sort= e.SortExpression.ToString();
   MyDataGrid.DataSource=dv;
   MyDataGrid.DataBind();
  }

  #region Web   override protected void OnInit(EventArgs e)
  {
   //   //
   InitializeComponent();
   base.OnInit(e);
  }
 
  /// <summary>  /// </summary>
  private void InitializeComponent()
  {   
   this.ddlWk.SelectedIndexChanged += new System.EventHandler(this.ddlWk_SelectedIndexChanged);
   this.Load += new System.EventHandler(this.Page_Load);

  }
  #endregion

  private void ddlWk_SelectedIndexChanged(object sender, System.EventArgs e)
  {
   Session["WP"]=ddlWk.SelectedValue;
   MyDataGrid.CurrentPageIndex=0;//没有这一句，当该页码超出其他数据源的范围时会出错
   BindGrid();
   Response.Write( "<script language='javascript'>parent.menuframe.location.reload();</script>");
 
  }