jquery 新建的元素事件绑定问题

<p class="file">图片标题：<input type="text" name="attachment_title[]" style="width:8em" /><input class="attachment" type="file" name="attachment[]" /><input type="button" class="del_attachment" value="删除"></p>
<mce:script type="text/javascript"><!--
var attachment_count = 1;

var attachment_change = function(){
if(attachment_count >= 3){
return false;
}
if($(this).parent().next().attr('class') != 'file'){
$(this).parent().after($(".file:first").clone(true).find(".attachment").change(attachment_change).end());
}
attachment_count++;
}
$(".attachment").change(attachment_change)

$(".del_attachment").click(function(){
$(this).parent().remove();
attachment_count--;
})
// --></mce:script>