Yii下拉列表在ivar onclick中保存值

how can I save value as ivar from dropDownlist in yii? here my code, which doesn't work :/ declaration of ivar:

public $blaaa;

and my dropdownlist code:

 echo CHtml::dropDownList(
                'categoryDropDownList',
                '',
                CHtml::listData(Category::model()->findAll(), 'id', 'name'),
                array(
                    'empty' => 'Select Category',
                    'onchange'=>function () {
                            $this->blaaa = 'js:this.value';
                        }
                    ));

I tried also with ajax, but it also doesnt work:

'ajax' => array(
    'type' => 'POST',
    'url' => CController::createUrl('category/actionBla'),
    'data' => array('id' => 'js:this.value')

where

public function bla()
{
    if (isset($_POST['id'])) {
         $this->blaaa = $_POST['id'];
}

thanks in advance for help!

I solved my problem with echo'ing CHtml::dropDownList in form:

echo CHtml::form();
    echo CHtml::dropDownList(
        'categoryDropDownList',
        '',
        CHtml::listData(Category::model()->findAll(), 'id', 'name'),
        array(
            'empty' => 'Select Category'
        ));
echo CHtml::endForm();

and now activeForm bother about sending parameters via POST

In ajax section, change url as below

'url' => CController::createUrl('category/bla'),

In controller, your function name should be

public function actionBla()