How to render combobox dropdownlist - extjs

Question

I am having trouble filtering an array store.
Situation
I have 2 comboboxes with an array store. combobox 1 and combobox 2, both are in mode 'local' and have a predefined array store. when i click and select a row in the first combobox, I apply a filter on the second combobox (which was not yet cliked upon). The thing is that the second combobox did not render it's data (or html) yet so the filter wasn't applied.
when i click on the second combobox, and then clicking on the first, the filter is applied and working.
my question is, how to pre-render an array_store/combobox?
I did try to expand the combobox first, but also didn't work for me. (see commented code)
var store1 = new Ext.data.ArrayStore({
fields: ['id','name'],
data:somedata //array of some data
});
var store2 = new Ext.data.ArrayStore({
fields: ['id','name'],
data:somedata //array of some data
});
var combobox1 = {
name: 'combobox_1',
xtype: 'combo',
hiddenName: 'combobox_1',
store: store1,
displayField:'name',
valueField:'id',
mode:'local',
triggerAction: 'all',
allowBlank:true,
emptyText:'Select...',
listeners:{
select: function(st, r){
var selected = r.get('name');
var combobox2 = Ext.getCmp('combobox2');
//combobox2.expand();
combobox2.store.filter([
{
property : 'name',
value : selected,
anyMatch : true,
caseSensitive: false
}
]);
},
scope:this
}
}
var combobox2 = {
name: 'combobox_2',
xtype: 'combo',
hiddenName: 'combobox_2',
store: store2,
id: 'combobox2'
displayField:'name',
valueField:'id',
mode:'local',
triggerAction: 'all',
allowBlank:true,
emptyText:'Select...',
}