extjs4 : chained combo

I'm trying to add some dynamic data into a "livesearch" combo box.

I've a set of 2 combos.

The first one allow you to select some data. The second combo is a "livesearch" combo that should have a dynamic parameter from the first combo. So the 2nd combo is linked to a model, which is linked to a datastore that queri开发者_运维百科es the server and outputs the data. But that data has to be filtered according to the first combo parameter...

Anyone knows how to do that ?

I did that before. The key is to pass the value of the first combo with the request for the values of the second combo, and then filter the results on the server. Other approach would be to load both combos with all possible values and then set a filter on the second combo's store after a value is selected in the first combo.

EDIT: Here's the I used.

Ext.define('Ext.ux.FilteredCombo', {
extend: 'Ext.form.field.ComboBox',
alias: 'widget.filteredcombo',

queryCaching: false,

getParams: function (queryString) {
    var params = this.callParent(arguments);
    if (Ext.isArray(this.formParams)) {
        var form = this.up('form');
        if (form) {
            var bf = form.getForm();
            for (var i = 0; i < this.formParams.length; i++) {
                var field = bf.findField(this.formParams[i]);
                if (field)
                    params[this.formParams[i]] = field.getValue();
            }
        }
    }
    return params;
}
});