[ExtJS] modx-tree-directory acting as a combo-box ? [SOLVED with combo-box !]]

{
      xtype:'modx-tree-directory',            
      rootId: 'assets/master/img/',
      name: 'folder',
      hideFiles: true,
      listeners: {
            click: function(n) {
                var lpath = n.attributes.id;
                var rem = 'assets/master/img/'
                var spath = lpath.replace(rem,'');
                Ext.Msg.alert('Navigation Tree Click', 'selected: "' + spath + '"'); // returns what I want but how to save this value as the value of field ?
            }
}

//[...]
fields: [{
    xtype: 'picman-combo-folders',
    fieldLabel: 'Folder',
    name: 'folder',
    hiddenName: 'folder',
    displayField: 'folder',
    valueField:'folder',
    anchor: '100%'
}]
//[...]

Picman.combo.Folders = function(config){
    config = config || {};
    Ext.applyIf(config,{
        id: 'picman-combo-folders',   
        url: Picman.config.connectorUrl,
        baseParams: {
            action: 'mgr/images/getListFolder'
        },
        store: new Ext.data.JsonStore({
            autoLoad: true,
            url: Picman.config.connectorUrl,
            baseParams: {
                action: 'mgr/images/getListFolder'
            },
            fields: ['folder']            
        })        
    });
    Picman.combo.Folders.superclass.constructor.call(this, config);
};
Ext.extend(Picman.combo.Folders,MODx.combo.ComboBox);
Ext.reg('picman-combo-folders',Picman.combo.Folders);

<?php

class picmanGetListFolderProcessor extends modProcessor {

    public $combo = true;

    public function process() {
        $assetspath = $this->modx->config['assets_path'];
        $dir = $assetspath . 'master/img';
        $stack[] = $dir;
        while ($stack) {
            $thisdir = array_pop($stack);
            if ($dircont = scandir($thisdir)) {
                $i = 0;
                while (isset($dircont[$i])) {
                    if ($dircont[$i] !== '.' && $dircont[$i] !== '..') {
                        $current_file = "{$thisdir}/{$dircont[$i]}";
                        if (is_file($current_file)) {
                            $path[] = "";
                        } elseif (is_dir($current_file)) {
                            $path[] = "{$thisdir}/{$dircont[$i]}";
                            $stack[] = $current_file;
                        }
                    }
                    $i++;
                }
            }
        }
        $lp = count($path);
        for ($x = 0; $x < $lp; $x++) {
            $suppr = $assetspath . 'master/img/';
            $fold = $path[$x];
            if ($fold != '') {
                $folder = str_replace($suppr, '', $fold);
                $myArray[] = $folder;
                $listtmp = array('folder' => $folder);
                $myArr[] = $listtmp;
            }
        }
        return $this->toJSON($myArr);
    }
}
return 'picmanGetListFolderProcessor';

            if ($dircont = scandir($thisdir)) {
                $i = 0;
                while (isset($dircont[$i])) {
                    if ($dircont[$i] !== '.' && $dircont[$i] !== '..') {
                        $current_file = "{$thisdir}/{$dircont[$i]}";
                        if (is_file($current_file)) {
                            $path[] = "";
                        } elseif (is_dir($current_file)) {
                            $path[] = "{$thisdir}/{$dircont[$i]}";
                            $stack[] = $current_file;
                        }
                    }
                    $i++;
                }
            }