ASP.net Validation for RadioButton - asp.net

Question

I want validation like, if i select Status as Reject then there must be some Comments(compulsory). and if status is Accept then comments may be blank (not compulsory)
How I will do it in ASP.NET, Please find my code
<tr>
<td width="30%">
<b>Status:</b>
</td>
<td>
<asp:RadioButton ID="lAccept" runat="server" AutoPostBack="True"
CausesValidation="True" Text="Accept" />
<asp:RadioButton ID="lReject" runat="server" AutoPostBack="True"
CausesValidation="True" Text="Reject " />
<asp:RequiredFieldValidator ID="RequiredFieldValidator6" runat="server"
ErrorMessage="Please Select it is Accepted or Rejected" ForeColor="Red"></asp:RequiredFieldValidator>
</tr>
<tr>
<td width="30%">
<b>Qty Rejected:</b>
</td>
<td>
<asp:TextBox ID="lRejectedQty" runat="server" CausesValidation="True"></asp:TextBox>
<%-- <asp:CustomValidator ID="CustomValidator1" runat="server"
ErrorMessage="Only interger between 1 to 10000000 " ondisposed="Page_Load"
oninit="Page_Load" onservervalidate="CustomValidator1_ServerValidate"></asp:CustomValidator>--%>
<asp:RangeValidator ID="RangeValidator3" runat="server"
ErrorMessage="Rejected Quantity must be in change of 1 to 10,000,000"
ControlToValidate="lRejectedQty" Display="Dynamic" ForeColor="Red"
MaximumValue="10000000" MinimumValue="1"></asp:RangeValidator>
</td>
</tr>
<tr> <td width="30%">
<b>Comments:</b>
</td>
<td>
<TEXTAREA rows=5 cols=40 name="lComments" id="lComments"></TEXTAREA>
</td>

Answer 1

The simplest way for this is to use a CustomValidator.
MSDN: https://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.customvalidator(v=vs.110).aspx
<asp:CustomValidator ID="CustomValidator1" runat="server"
ErrorMessage="You must enter Comments if you choose to Reject."
OnServerValidate="CustomValidator1_ServerValidate">
</asp:CustomValidator>
Then in your code-behind you may do more detailed checks for it being valid or not
protected void CustomValidator1_ServerValidate(object sender, ServerValidateEventArgs e)
{
e.IsValid = true; // set it to be valid by default
if (lReject.Checked == true && string.IsNullOrWhiteSpace(lComments.Text) == true)
{
// Reject was selected and no comments were entered
e.IsValid = false;
}
}
The drawback is that this requires a PostBack to the server and will validate after the other types in most cases.