Extjs的combobox默认值问题

Extjs的combobox有一个value属性用于指定默认值，但下面只显示“3”var city=[[0,'博士'],[1,'硕士'],[2,'学士'],[3,'本科'],[4,'大专'],[5,'中专'],[6,'高中'],[7,'初中或以下']]; var proxy=new Ext.data.MemoryProxy(city); var citycol=new Ext.data.Record.create([
{name:'cid',type:'int',mapping:0},
{name:'cname',type:'string',mapping:1}
]); var reader=new Ext.data.ArrayReader({},citycol); var store=new Ext.data.Store({
proxy:proxy,
reader:reader,
autoLoad:true
}); var combobox=new Ext.form.ComboBox({
//renderTo:'combobox',
triggerAction:'all',
store:store,
displayField:'cname',
valueField:'cid',
fieldLabel:'学历',
model:'local',
emptyText:'请选择',
editable:false,
value:3 });