c# - fill dropdownlist from onselectindexchanged -

im using asp.net , c#

im using 2 dropdownlist dd1,dd2

how fill 2nd dropdownlist dd2 dd1 onselectindexchanged

my code is,

 <asp:dropdownlist id="ddmedtype" runat="server" cssclass="drop" autopostback="true" onselectedindexchanged="ddmedtype_selectedindexchanged">                 <asp:listitem value="0">-select-</asp:listitem>                 <asp:listitem value="tablet">tablet</asp:listitem>                 <asp:listitem value="tonic">tonic</asp:listitem>                 <asp:listitem value="capsules">capsules</asp:listitem>                 <asp:listitem value="dispotab">disposable tablet</asp:listitem>             </asp:dropdownlist>   <asp:dropdownlist id="ddmedname" runat="server" cssclass="drop" >                 <asp:listitem value="0">-select-</asp:listitem>             </asp:dropdownlist>   protected void ddmedtype_selectedindexchanged(object sender, eventargs e)     {         string medtype = ddmedtype.selecteditem.text;         string str = "select medicinename,medicineid medicinemaster medicinetype = '" + medtype + "'";         cmd = new sqlcommand(str, con);         sqldatareader reader = cmd.executereader();         while (reader.read())         {               ddmedname.selectedvalue= reader["medicineid"].tostring();           }     } 

here condition returns 2 items, dropdownlist dd2 returns 1 ...

you setting selectedvalue, not mean you're adding or removing items in dropdownlist

datatable medicines= new datatable();  using (sqlconnection con = new sqlconnection(connectionstring)) {      try     {         sqldataadapter adapter = new sqldataadapter("select medicinename,medicineid medicinemaster medicinetype = '" + medtype + "'", con);         adapter.fill(subjects);          ddmedname.datasource = subjects;         ddmedname.datatextfield = "medicinename";         ddmedname.datavaluefield = "medicineid";         ddmedname.databind();     }     catch (exception ex)     {         // handle error     }  }  // add initial item - can add if options // db not loaded ddmedname.items.insert(0, new listitem("-select-", "0")); 

you can reader follows:

ddmedname.items.clear(); ddmedname.items.add(new listitem("-select-", "0")); while (reader.read()) {   ddmedname.items.add(new listitem(reader["medicinename"].tostring(), reader["medicineid"].tostring()); }