[Wiki] An Easy Solution for Dependent dropDownList Using AJAX

<?php                                   
  echo CHtml::dropDownList('region_id','', 
  array(2=>'New England',1=>'Middle Atlantic',3=>'East North Central'),
 
  array(
    'prompt'=>'Select Region',
    'ajax' => array(
    'type'=>'POST', 
    'url'=>CController::createUrl('loadcities'),
    'update'=>'#city_name', 
  'data'=>array('region_id'=>'js:this.value'),
  ))); 
 
 
 
echo CHtml::dropDownList('city_name','', array(), array('prompt'=>'Select City'));
?>

public function actionLoadcities()
{
   $data=RegionCity::model()->findAll('region_id=:region_id', 
   array(':region_id'=>(int) $_POST['region_id']));
 
   $data=CHtml::listData($data,'id','city_name');
 
   echo "<option value=''>Select City</option>";
   foreach($data as $value=>$city_name)
   echo CHtml::tag('option', array('value'=>$value),CHtml::encode($city_name),true);
}