How to know form submit sucessfully in yii - yii

Question

i want to submit button disable when form submitted sucessfully, because user click submit button so many times when page loading so its saved the same records so many times.so i want to decided to when form submit sucessfully mean disable that submit button.i am also using aftervalidate function but it can't correct form submit successfull.
My Coding:
<?php
$form = $this->beginWidget('CActiveForm', array(
'id' => 'question-form',
// Please note: When you enable ajax validation, make sure the corresponding
// controller action is handling ajax validation correctly.
// There is a call to performAjaxValidation() commented in generated controller code.
// See class documentation of CActiveForm for details on this.
'enableAjaxValidation' => true,
'enableClientValidation' => false,
'clientOptions' => array(
'validateOnSubmit' => true,
'validateOnChange' => false,
'afterValidate' => 'js:buttondisable',
),
));
?>
<div class="form-group">
<?php echo $form->labelEx($model, 'question_title'); ?>
<?php echo $form->textField($model, 'question_title', array('size' => 50, 'maxlength' => 250, 'class' => 'form-control')); ?>
<?php echo $form->error($model, 'question_title'); ?>
</div>
<?php if ($tileAssigned == Yii::app()->const->FLAG_ZERO) { ?>
<div class="form-group">
<?php echo $form->labelEx($model, 'type', array('label' => 'Is Multiple Choice')); ?>
<?php echo $form->radioButtonList($model, 'type', $yesnoList, array('separator' => '', 'onchange' => 'questionTypeChange(this.value);', 'class' => '')); ?>
<?php echo $form->error($model, 'type'); ?>
</div>
But After validation function calling when validation done in every time,but i want to form submit sucessfully at this time disable button.