[jQuery] livequery $(this) is null?

[wahyudinata]

jQuery.create_table.prepare_add_item=function()
{
        var items=$('#canvas > thead > tr > th');
        var prev_value='';
        var input_item=$('#input_item');
        var head=$('#canvas > thead > tr');

       // FIRST METHOD
        $('#canvas > thead > tr > th').click(
                function()
                {
                        alert($(this).attr('id'));
                }
        );
///SECOND METHOD
        $('#canvas > thead > tr > th').livequery(
                        function()
                        {
                                $(this).click(function(){
                                        alert($(this).attr('id'));
                                })
                        }
        );
        //THIRD METHOD
        $('#canvas > thead > tr > th').livequery('click',
                function(event)
                {
                        var elem=$(this);
                        alert(elem.attr('class'));
                        if (elem.is('.manipulated'))return;

                        elem.addClass('manipulated');//add class that it is 
being
manipulated
                        prev_value=elem.html();//store whatever it's in here 
before
                //      alert(elem.id);
                        elem.empty();
                        elem.append(input_item);

                }

        );