I look for the API of comboxbox (which is pretty useless), it mentions if I want to set the combobox list (lower part) width, use listWidth, but I try it and it doesn't work.

var txtPrice = Ext.create('Ext.form.field.ComboBox', {
id: 'txtPrice',
name: 'txtPrice',
xtype: 'combo',
hidden: false,
mode: 'local',
queryMode: 'local',
triggerAction: 'all',
emptyText: '(Input Price Here)',
resizable: false,
store: store7,
autoLoad: false,
minChars: 1,
matchFieldWidth: false,
minListWidth: 320,
listWidth: 320,
autoSelect: true,
enableKeyEvents: true,
loadingText: "wait...",
selectOnFocus: true,
listeners: {
loadexception: {
fn: function (proxy, store, response, e) {
Ext.MessageBox.alert(alert_lbl, "Fail Loading Price");
}, scope: this
select: function (combo, record, index) {
// var val = record[0].get("PriceList");
// val = trim(val);
// this.setRawValue(val);
blur : function() {
var val = this.getRawValue();
val = trim(val);
expand: function (combo) {
//var compcode = Ext.getCmp('selectedSymbol').getValue();
var compcode = formPanel.down('[name=txtSelectedSymbol]').getValue();
//store7.load({ params: { cocode : compcode } });

How to make the list width 320px?