Radiobutton Validation inside Gridview

Following Code Explains How to Validate Radio button inside a Grid view Using Custom Validator. 

 .aspx Page

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false" >
        <Columns>
            <asp:TemplateField>
                <ItemTemplate>
                   <asp:RadioButton ID="rb" runat="server" />
                </ItemTemplate>
            </asp:TemplateField>
            <asp:BoundField DataField="RowNumber" HeaderText="Row Number" />
            <asp:BoundField DataField="Col1" HeaderText="First Column" />
            <asp:BoundField DataField="Col2" HeaderText="Second Column" />
        </Columns>
</asp:GridView>

 <br />
    <asp:Label ID="lblMessage" runat="server" />
    <br />
    <asp:Button ID="btn" runat="server" Text="POST" onclick="btn_Click" ValidationGroup="GroupA" />
    <asp:CustomValidator ID="CustomValidator1" runat="server" ErrorMessage="Please select row in the grid." ClientValidationFunction="ValidateRadioButton" ValidationGroup="GroupA" style="display:none"></asp:CustomValidator>
    <asp:ValidationSummary ID="ValidationSummary1" runat="server" ValidationGroup="GroupA" HeaderText="Error List:" DisplayMode="BulletList" ForeColor="Red" />  

JavaScript Function :

function ValidateRadioButton(sender, args) {
        var gv = document.getElementById("<%= GridView1.ClientID %>");
        var items = gv.getElementsByTagName('input');
        for (var i = 0; i < items.length ; i++) {
            if (items[i].type == "radio") {
                if (items[i].checked) {
                    args.IsValid = true;
                    return;
                }
                else {
                    args.IsValid = false;
                }
            }
        }
}