public partial class _Default : System.Web.UI.Page {     protected string title="大家好";            //前台代码<title><%#title %></title>     protected void Page_Load(object sender, EventArgs e)     {         DataSet ds = new DataSet();         string sql = ConfigurationManager.ConnectionStrings["strsql"].ConnectionString;         using (SqlConnection sqlCnn=new SqlConnection(sql))         {             using (SqlCommand sqlCmm=sqlCnn.CreateCommand())             {                 sqlCmm.CommandText = "select * from List";                 SqlDataAdapter adapter = new SqlDataAdapter(sqlCmm);                 adapter.Fill(ds);             }             this.RadioButtonList1.DataSource = ds.Tables[0];             this.RadioButtonList1.DataTextField = "listname";             this.RadioButtonList1.DataValueField = "id";             //this.RadioButtonList1.DataBind();             this.CheckBoxList1.DataSource = ds.Tables[0];             this.CheckBoxList1.DataTextField = "listname";             this.CheckBoxList1.DataValueField = "id";             //this.RadioButtonList1.DataBind();             this.DataBind();         }            //数据绑定到RadioButtonList,CheckBoxList         if (!IsPostBack)         {             DataSet ds1 = new DataSet();             using (SqlConnection sqlCnn1 = new SqlConnection(sql))             {                 using (SqlCommand sqlCmm1 = sqlCnn1.CreateCommand())                 {                     sqlCmm1.CommandText = "select provinceid,provincename from Province";                     SqlDataAdapter adapter = new SqlDataAdapter(sqlCmm1);                     adapter.Fill(ds1);                     this.DropDownList1.DataSource = ds1.Tables[0];                     this.DropDownList1.DataTextField = "provincename";                     this.DropDownList1.DataValueField = "provinceid";                     this.DropDownList1.DataBind();                 }             }         }     }     protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)     {         DataSet ds = new DataSet();         string str = ConfigurationManager.ConnectionStrings["strsql"].ConnectionString;         using (SqlConnection sqlCnn = new SqlConnection(str))         {             using (SqlCommand sqlCmm = sqlCnn.CreateCommand())             {                 sqlCmm.CommandText = "select cityid,cityname from City where provinceid='" + this.DropDownList1.SelectedValue + "'";                 SqlDataAdapter adapter = new SqlDataAdapter(sqlCmm);                 adapter.Fill(ds);                 this.DropDownList2.DataSource = ds.Tables[0];                 this.DropDownList2.DataTextField = "cityname";                 this.DropDownList2.DataValueField = "cityid";                 this.DropDownList2.DataBind();             }         }     }//实现省市二级联动 }