Radio Button Check Changed even not firing

I've 2 radio buttons in a user control and control is registered to the page. When i click on the radio button, the event(CheckChanged) is not firing.

<asp:View ID="viewfirst" runat="server">
                    <asp:UpdatePanel ID="updatepanel1" runat="server" UpdateMode="Always">
                        <ContentTemplate>

                            <asp:RadioButton ID="radio1" Text="Yes" Enabled="true" runat="server" />
                            <asp:RadioButton ID="radio2" Text="No" Enabled="true" runat="server" />
                        </ContentTemplate>
                    </asp:UpdatePanel>
                </asp:View>

Below is code in behind file of the control. 


 Protected Sub radio1_CheckedChanged(sender As Object, e As EventArgs) Handles radio1.CheckedChanged
    //
    //
End Sub

It seems everything looks good, but something is wrong. Can you please let me know.