OnSelectedIndexChanged event of RadioButtonList is not firing

Question

I have a RadioButtonList in asp.net. I am trying to do a simple thing i.e. to display or hide a div on changing the radio buttons from the list.But the event OnSelectedIndexChanged is not firing. I am not getting the reason. This is the code

<asp:RadioButtonList ID="CityStateZip" runat="server" ForeColor="#333300" AutoPostBack="true" RepeatDirection="Horizontal"  Width="274px" CausesValidation="true" ValidationGroup="SchoolSearchGroup"  OnSelectedIndexChanged="CityStateZip_SelectedIndexChanged">
                <asp:ListItem  Value="1" Text="City and State" />
                <asp:ListItem Value="2" Text="Zip Code" />
</asp:RadioButtonList>
<div id="zipcodediv" runat="server" visible="false" style="margin-left:75px">
 code.........
</div>
<div id="citystatediv" runat="server" style="margin-left:75px; width: 708px;">
code........
</div>

Code behind

 protected void CityStateZip_SelectedIndexChanged(Object sender,EventArgs e)
    {           
        if (CityStateZip.SelectedValue == "1")
        {               
            zipcodediv.Visible = false;
            citystatediv.Visible = true;
        }
        if (CityStateZip.SelectedValue == "2")
        {                
            citystatediv.Visible = false;
            zipcodediv.Visible = true;
        }
    }

Answer 1

I had the same problem as you and fixed it by adding AutoPostBack="true" to my RadioButtonList's definition in the ASPX. It appears you have that in your definition already, but for anyone else who comes in here after this might be all you need.