Try this:
ClientSide:
Javascript:
<script language="javascript" type="text/javascript" >
function validate() {
if (document.getElementById('<%=DropDownList1.ClientID %>').value == "Select") {
alert("Please Select!");
document.getElementById('<%=DropDownList1.ClientID %>').focus();
return false;
}
}
</script>
Markup:
<asp:button id="Button1" runat="server" text="Button" onclick="Button1_Click" onclientclick="return validate()"/>
ServerSide:
In .CS page:
DropDownList1.Items.Insert(00, "Select");
DropDownList1.SelectedIndex = 0;
In button click event:
if (ddl_DropDownList1.SelectedItem.Text != "Select")
{
}
else
{
}