Three-level linkage of provincial and municipal level implemented with DropDownList

This is a DropDownList implementation of the provincial and municipal level three linkage, record the

<asp:scriptmanager id= "ScriptManager1" runat= "Server" >/asp:ScriptManager>

<asp:updatepanel id= "UpdatePanel1"  runat= "Server" >                           <contenttemplate><p><span class= "Redcolor" >* </span> Select a region:                           <asp:dropdownlist id= "Provinceselect"  autopostback= "True"  &nbs p;runat= "Server"  onselectedindexchanged= "Getcityname_onclick" ></asp:dropdownlist><asp:d ropdownlist runat= "Server"  id= "Cityselect"  autopostback= "True"  onselectedindexchanged= " Getcounty_onclick "  ></asp:dropdownlist><asp:dropdownlist   autopostback= "True"  runat= "Server"  id= "County" ></asp:DropDownList></p>                        </ contenttemplate>                          <Triggers>                              <asp:asyncpostbacktrigger controlid= "Provinceselect"  EventName= " SelectedIndexChanged " />                         </Triggers>
</asp:UpdatePanel>

Background code:

protected void Page_Load (object sender, EventArgs e)        {            if (!  IsPostBack)            {                Provinceselect.datasource = BFL. Getprivoces ();                Provinceselect.datatextfield = "Regionname";                Provinceselect.datavaluefield = "RegionID";                Provinceselect.databind ();                ProvinceSelect.Items.Insert (0, New ListItem ("Please select", String.) Empty)); CitySelect.Items.Insert (0, New ListItem ("Please select", String.) Empty)); County.Items.Insert (0, New ListItem ("Please select", String.) Empty));  } }

#region Provinces and Cities data binding//city-bound public void Getcityname_onclick (object sender, EventArgs e) {citys Elect. DataSource = BFL. Getcitys (int.            Parse (ProvinceSelect.SelectedItem.Value));            Cityselect.datatextfield = "Regionname";            Cityselect.datavaluefield = "RegionID";            Cityselect.databind (); County.Items.Insert (0, New ListItem ("Please select", String.)        Empty)); }
County-bound public void Getcounty_onclick (object sender, EventArgs e) {county.datasource = BFL. Getcitys (int.            Parse (CitySelect.SelectedItem.Value));            County.datatextfield = "Regionname";            County.datavaluefield = "RegionID";            County.databind (); County.Items.Insert (0,new ListItem ("Please select", String.)        Empty)); } #endregion

Three-level linkage of provincial and municipal level implemented with DropDownList