Ext combobox 的动态改变

handler : function(btn) {
var sorce = win.grid1.getSelections();
var obj = windows['adddriverWindwo'];
if (sorce.length <= 0) {
alert('请选择要增加司机的车辆!');
return false;
}
obj.vehicleid.setValue(sorce[0].get('vehicle_id'));
obj.multicomboboxJsonStore.proxy = new Ext.data.HttpProxy({
url : 'servlet/ComboBoxServlet?comboxname=holddrivers&vehicleid='+sorce[0].get('vehicle_id')
});
obj.multicomboboxJsonStore.reload();
obj.show();
}