关于Ext如果动态生成 form 下拉框的，并且可以动态改变内容可以改变刷新的方法：

需要效果如下图：

直接上代码：

<?xml version="1.0" encoding="UTF-8"?>
<Application title="报表查询(汇总分类)"  version="ext4"  xmlns="http://www.w3school.com.cn" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.w3school.com.cn /schema/Application.xsd"
			 script="/appreport/report/js/reportList.js">
	<TabPanel ID="tabpanel" ref="tabpanel">
		<Panel ID="panel_1" title="报表查询(汇总分类)"  layout="border" ref="panel_1" >

			<Form ID="classify"  region="north" layout="form" height="85"   ref="classify" autoScroll="false">
				<FieldSet title="选择类别" colspan="2"  columnLength="2" height="80" columnWidths="[0.5,0.5]">
				     <column title="报表分类" allowBlank="true"  editable="false" type="combo" url='/ireport/report/selectRqreportClassification'
					 valueField="classification" displayField="classification" root="classifys" name="classification" width="120" loadstore="true" 
					 onChange="classification_change_handle"/>
				</FieldSet>
			</Form>
			<Grid title="报表信息"  ID="reportlist" region="center" flex="1" baseParams="{'cond.auditflag':'0'}"
				  url='/ireport/report/selectReportList' root="rqreportInfos"
				  loadstore="true" splitPage="true" pkname="rid" ref="reportlist" >
				<column type="checkBox"/>
				<column title="报表ID" name="rid" />
				<column title="名称" name="reportname" width="200"  renderer="to_query"/>
				<column title="报表文件" name="reportfile" width="160" />
				<column title="报表分类" name="classification"/>
				<column title="备注" name="remark"  />
				<column title="单位名称" name="corpdesc" width="160" />
				<column title="制单人编码" name="recordercode" />
				<column title="制单人名称" name="recorderdesc" />
				<column title="制单时间" name="recordtime"  type="datefield"/>
			</Grid>

		</Panel>
	</TabPanel>
</Application>


function classification_change_handle() {
	var classify = Ext.getCmp('classify')
	var newValue = classify.getField('classification').getValue();

    var theGrid = Ext.getCmp('reportlist');
    var extraParams = theGrid.getStore().getProxy().extraParams;
	var vparams="";
	if("所有分类"==newValue){
		vparams = {'cond':{'auditflag':'0'}};
	}else {
		vparams = {'cond':{'auditflag':'0','classification':newValue}};
	}
    extraParams['jsonString'] = Ext.JSON.encode(vparams);
    theGrid.loadList();
}

 其中url那部分返回值信息如下