selectedindexchanged event is not firing in asp.net with opn

Question

please help me i'm facing a problem with dropdown list i'm using javascript method "onchange" to get dropdown selected value i get the value but dropdown selectedIndexChanged event not firing  please someone help me

my javascript function is that for getting selected value:

 <script type="text/javascript" language="javascript">

        function showAddress_Byamit()

         {

             var e = document.getElementById("TabC_tp1_ddlcountry");

             var country = e.options[e.selectedIndex].text;

          }

</Script>

it works well but the problem in codebehind

<asp:DropDownList 

                ID="ddlcountry" runat="server" AutoPostBack="True" Height="20px" EnableViewState="true"

                OnSelectedIndexChanged="ddlcountry_SelectedIndexChanged" TabIndex="4"  onchange="showAddress_Byamit(); return false"

                Width="100px" ></asp:DropDownList>

here problem is that event "ddlcountry_SelectedIndexChanged" not firing

and in codebehind i add Onchange event as:

  ddlcountry.Attributes.Add("onchange", "showAddress_Byamit(); return false");