easyui-combo下拉框

$('#box').combo({
required:true,
multiple:true,
width:200,
height:50,
panelWidth:300,
panelHeight:200,
multiple:true,
onShowPanel:function(){
alert('下拉的時候觸發');
},
onChange:function(){
alert('字段值改變的時候觸發');
},
});