The picker er implemented in the combobox by the function createPicker. If you see the code you will find that the picker is a view.BoundList. A boundlist has no property dockedItems, because that is a property of a panel.
What you can do is override the createPicker function
Code:
createPicker: function() {
var me = this,
picker,
pickerCfg = Ext.apply({
xtype: 'boundlist',
pickerField: me,
selModel: {
mode: me.multiSelect ? 'SIMPLE' : 'SINGLE'
},
floating: true,
hidden: true,
store: me.store,
displayField: me.displayField,
focusOnToFront: false,
pageSize: me.pageSize,
tpl: me.tpl
}, me.listConfig, me.defaultListConfig);
picker = me.picker = Ext.widget(pickerCfg);
if (me.pageSize) {
picker.pagingToolbar.on('beforechange', me.onPageChange, me);
}
me.mon(picker, {
itemclick: me.onItemClick,
refresh: me.onListRefresh,
scope: me
});
me.mon(picker.getSelectionModel(), {
beforeselect: me.onBeforeSelect,
beforedeselect: me.onBeforeDeselect,
selectionchange: me.onListSelectionChange,
scope: me
});
return picker;
},
and place the boundlist on a panel.