在ajax调用yii的renderPartial中的TbActiveForm dropDownListRow

I am quiet new in Yii. I am trying to generate Dependent dropdown field using ajax I had one view file name swap.php andhaving the following code included in it

<?php $form=$this->beginWidget('bootstrap.widgets.TbActiveForm',array(
    'id'=>'projects-form',
    'type'=>'horizontal',
    'enableAjaxValidation'=>false,
    'enableClientValidation'=>true,
    'htmlOptions'=>array(
        'enctype'=>"multipart/form-data"
    )
)); ?>

<?php echo $form->dropDownListRow($model, 'salesperson', $data,array('labelOptions'=>array('label'=>'Select Sales Person'),'empty'=>array(''=>'Choose Sales Person'), 'class'=>'span3','maxlength'=>5,
'ajax'=>array(
    'type'=>'POST',
    'url'=>$this->createUrl('getUsers'),
    'update'=>'#SalesPersonsAssignLog_users'
)
)); 
?>
<div id="SalesPersonsAssignLog_users">

</div>

<?php $this->endWidget(); ?>

in the corresponding controller I had the following function

public function actionGetUsers()
    {

        $result         =   $_POST['SalesPersonsAssignLog'];
        $salesPersonId  =   $result['salesperson'];         
        $model              =   new UsersSalesPersons;
        $result             =   $model->getAssignedCompanies($salesPersonId);
        $resultArray        =   array();
        foreach($result as $value)
        {
            $id     =   $value->company->user_id;
            $name   =   $value->company->user_company;
            $resultArray[$id]   =   $name;          
        }
        $this->renderPartial('_ajaxUsers',array('data'=>$resultArray,'model'=>$model));     

    }

the __ajaxUsers.php I need to create a dropdownListRow using TbActive form,

<?php echo $form->dropDownListRow($model, 'users', $data,array('labelOptions'=>array('label'=>'Sales Person'),'empty'=>array(''=>'Choose Sales Person'), 'class'=>'span3','maxlength'=>5)); ?>

Got a fatal error Call to a member function dropDownListRow() on a non-object as no TbActiveForm include in this page, Then how can I create a dropdownListRow on ajax call

You have to initialize $form as TbActiveForm widget and give it path to TbActiveForm file

 $form = $this->beginWidget( 'ext.bootstrap.widgets.TbActiveForm', array(
        'id'                    => 'test-form'
 ) );

Don't forget to end widget

$this->endWidget();