How to validate asp:CheckBox?

To validate asp:Checkbox, you can't use RequiredFieldValidator. If you try to use RequiredFieldValidator, it will throw following error.

Control 'chkAgreed' referenced by the ControlToValidate property of 'ReqFieldValidatorId' cannot be validated.

So you need to use CustomValidator. Following is the code snippet

ASP.NET Code

<asp:CheckBox ID="chkAgreed" runat="Server" Text="I agree." ForeColor="green" Font-Bold="true" />
    <asp:CustomValidator ClientValidationFunction="ValidateCheckBox" runat="server" ID="cvf" />

JavaScript Code

<script language="javascript" type="text/javascript">
    function ValidateCheckBox(source, args)
    {
        if(document.all["<%= chkAgreed.ClientID %>"].checked == false)
            {
            alert("Please check the checkbox to proceed.");
            args.IsValid = false;
        }
    }
</script>

Thanks