jQuery Validate - at least one from a group of checkboxes is checked only if a radio button is checked

Question

I´m using jquery validate plugin to ensure at least one from a group of three checkboxes is checked and it´s woking fine. But I want validate these checkboxes only if the radio button "Sim" is checked. I don´t know how to do this.

Demo: http://jsfiddle.net/TnmGr

Html Form:

<form name="itemForm" id="itemForm" method="post">
<p>
  <input name="resp01" type="radio" value="sim" id="resp01-sim" class="resp" /> <label for="resp01-sim">Sim</label>
  <input name="resp01" type="radio" value="não" id="resp01-nao" class="resp" /> <label for="resp01-nao">Não</label>
</p>
<fieldset style="width:200px"><legend>Outros catalogos</legend>
<input id="opt01" name="opt01" type="checkbox" value="true" class="require-one" />
<label for="opt01">opt01</label>
<input name="opt01" type="hidden" value="false" /><br />

<input id="opt02" name="opt02" type="checkbox" value="true" class="require-one" />
<label for="opt02">opt02</label>
<input name="river2" type="hidden" value="false" /><br />

<input id="opt03" name="opt03" type="checkbox" value="true" class="require-one" />
<label for="opt03">opt03</label>
<input name="opt03" type="hidden" value="false" /><br />
</fieldset>
<div class="error" id="form_error"></div>
<br />
<input type="submit" />

JS:

$.validator.addMethod('require-one', function(value) {
    return $('.require-one:checked').size() > 0;
}, 'Selecione pelo menos uma das opções.');

$(document).ready(function(){

    var checkboxes = $('.require-one');
    var checkbox_names = $.map(checkboxes, function(e, i) {
        return $(e).attr("name")
    }).join(" ");

    $("#itemForm").validate({
        groups: {
            checks: checkbox_names
        },
        rules: {
            resp01: 'required',
        },
        messages: {
            resp01:  { required: 'Selecione uma resposta!' },
        },
        errorPlacement: function(error, element) {
            $('#form_error').append(error);
        },
        submitHandler: function(form) {
            alert('Form Submited');
            return false;
        }        

    });
});

Answer 1

You simply need to alter the logic of your custom method.

$.validator.addMethod('require-one', function(value) {
    if ($('#resp01-sim').is(':checked')) {
        return $('.require-one:checked').size() > 0;
    } else {
        return true;
    }
}, 'Selecione pelo menos uma das opções.');

DEMO: http://jsfiddle.net/TnmGr/4/