extjs4.2 中怎么给文本框textfield加事件

{
xtype: 'textfield',
width: 320,
fieldLabel: '加倍数',
name:'check.num',
value:'1',
listeners:{
change:function(t,newV,oldV,eOpts ){
var form = Ext.getCmp('checkForm'+me.siteId).getForm();
var jb = form.findField('check.reason');
if(newV!='1'){
jb.setReadOnly(false);
}else{
jb.setValue("");
jb.setReadOnly(true);
}
}
}
}

listeners:{ }