asp.net 实现省市级联-----<简单方法1>

<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<asp:DropDownList ID="DropDownList1" runat="server"
onselectedindexchanged="DropDownList1_SelectedIndexChanged"
ontextchanged="DropDownList1_TextChanged" AutoPostBack=true>
</asp:DropDownList>
<br />
<asp:DropDownList ID="ddl_city" runat="server"
onselectedindexchanged="ddl_city_SelectedIndexChanged">
</asp:DropDownList>
</ContentTemplate>
</asp:UpdatePanel>

protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
string sqlstr = "select * from promary";
DataTable dt = sqlhelper.ExcuteDataTable(sqlstr);
//1.显示什么数据
DropDownList1.DataTextField = "proName";
DropDownList1.DataValueField = "proId";
DropDownList1.DataSource = dt;
DropDownList1.DataBind();
}

}

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
string proId = DropDownList1.SelectedValue.ToString();
string sqlstr = string.Format("select * from city where proID={0}", proId);
DataTable dt = sqlhelper.ExcuteDataTable(sqlstr);
ddl_city.DataTextField = "cityName";
ddl_city.DataValueField = "cityId";
ddl_city.DataSource = dt;
ddl_city.DataBind();
}