K2 Component category Selection Custom Field- Joomla

<?php
/*------------------------------------------------------------------------
# k2cat.php - System - Next Previous Article
# ------------------------------------------------------------------------
# author    Codeboxr Team
# copyright Copyright (C) 2010-2013 codeboxr.com. All Rights Reserved.
# @license - http://www.gnu.org/licenses/gpl-2.0.html GNU/GPL
# Websites: http://codeboxr.com
# Technical Support:  Forum -   http://codeboxr.com/product/show-next-previous-article-plugin-for-joomla
-------------------------------------------------------------------------*/

// no direct access
defined('_JEXEC') or die('Restricted access');

if(version_compare(JVERSION,'3.0.0','ge')):
    jimport('joomla.form.formfield');
    class JFormFieldK2cat extends JFormField {

            protected $type = 'k2cat';

            public function getInput(){
                //$this->name, $this->value, $this->element, $this->options['control']
                //var_dump($this);
                //$value =
                $db = JFactory::getDBO();
                if(JFile::exists(JPATH_ROOT.DIRECTORY_SEPARATOR.'components'.DIRECTORY_SEPARATOR.'com_k2'.DIRECTORY_SEPARATOR.'k2.php')):
                    $query = 'SELECT m.* FROM #__k2_categories m WHERE published=1 AND trash = 0 ORDER BY parent, ordering';
                    $db->setQuery( $query );
                    $mitems = $db->loadObjectList();
                    //var_dump($mitems);
                    $children = array();
                    if ($mitems){
                        foreach ( $mitems as $v ){
                            if(K2_JVERSION != '16'){
                                    $v->title = $v->name;
                                    $v->parent_id = $v->parent;
                            }
                            $pt = $v->parent;
                            $list = @$children[$pt] ? $children[$pt] : array();
                            array_push( $list, $v );
                            $children[$pt] = $list;
                        }
                    }
                    $list = JHTML::_('menu.treerecurse', 0, '', array(), $children, 9999, 0, 0 );
                    $mitems = array();

                    foreach ( $list as $item ) {
                        $item->treename = JString::str_ireplace('&#160;', '- ', $item->treename);
                        $mitems[] = JHTML::_('select.option',  $item->id, '   '.$item->treename );
                    }



                $fieldName = $this->name.'[]';


                //$doc->addScriptDeclaration($js);
                $output = JHTML::_('select.genericlist',  $mitems, $fieldName, 'class="inputbox" style="width:220px;" multiple="multiple" size="10"', 'value', 'text', $this->value );
                return $output;

              endif;
               return;
                //return JElementK2cat::fetchElement($this->name, $this->value, $this->element, $this->options['control']);
          }
    }
else:
    if(version_compare(JVERSION,'1.6.0','ge')) {
            jimport('joomla.form.formfield');
            class JFormFieldK2cat extends JFormField {

                    var $type = 'k2cat';

                    function getInput(){
                            return JElementK2cat::fetchElement($this->name, $this->value, $this->element, $this->options['control']);
                    }
            }
    }

    jimport('joomla.html.parameter.element');

    class JElementK2cat extends JElement
    {

            var $_name = 'k2cat';

            function fetchElement($name, $value, &$node, $control_name){

                    $db = JFactory::getDBO();

                    if(JFile::exists(JPATH_ROOT.DIRECTORY_SEPARATOR.'components'.DIRECTORY_SEPARATOR.'com_k2'.DIRECTORY_SEPARATOR.'k2.php')):
                        $query = 'SELECT m.* FROM #__k2_categories m WHERE published=1 AND trash = 0 ORDER BY parent, ordering';
                        $db->setQuery( $query );
                        $mitems = $db->loadObjectList();
                        $children = array();
                        if ($mitems){
                            foreach ( $mitems as $v ){
                                //if(K2_JVERSION != '16'){
                                        $v->title = $v->name;
                                        $v->parent_id = $v->parent;
                                //}
                                $pt = $v->parent;
                                $list = @$children[$pt] ? $children[$pt] : array();
                                array_push( $list, $v );
                                $children[$pt] = $list;
                            }
                        }
                        $list = JHTML::_('menu.treerecurse', 0, '', array(), $children, 9999, 0, 0 );
                        $mitems = array();

                        foreach ( $list as $item ) {
                            $item->treename = JString::str_ireplace('&#160;', '- ', $item->treename);
                            $mitems[] = JHTML::_('select.option',  $item->id, '   '.$item->treename );
                        }


                    if(version_compare(JVERSION,'1.6.0','ge')) {
                        $fieldName = $name.'[]';
                    }
                    else {
                        $fieldName = $control_name.'['.$name.'][]';
                    }

                    $output= JHTML::_('select.genericlist',  $mitems, $fieldName, 'class="inputbox" style="width:90%;" multiple="multiple" size="10"', 'value', 'text', $value );
                    return $output;

                endif;
                    return;
            }
    }
endif;