Dynamically changing the jQuery sortable placeholder value

How do I use an if statement in the jQuery sortable plugin to dynamically determine the placeholder class?

If the item 开发者_如何学Cis being dragged around in #listA then I want the placeholder class to be .ImInListA

If the item is being dragged around in #listB then I want the placeholder class to be .ImInListB

jQuery

$( "#listA, #listB" ).sortable({
    connectWith: ".connected_sortable",
    placeholder:
    //if the current item is being dragged in #listA
    //use css class selector .ImInListA
    //else
    //use css class selector .ImInListB
}).disableSelection();

HTML:

<ul id="listA" class="connected_sortable">
  <li value="1">list_a_1</li>
</ul>

<ul id="listB" class="connected_sortable">
  <li value="2">list_b_2</li>
</ul>

Thanks!

I do it like this:

$("#listA li").live('mouseover', function(){
 $( "#listA" ).sortable( "option", "placeholder", 'ImInListA' );
});

$("#listB li").live('mouseover', function(){
 $( "#listB" ).sortable( "option", "placeholder", 'ImInListB' );
});

Hope this help someone :)