how to pass the parameter to actionID which can only be access by argument not by $_GET['parameter_name'] ?

my actionID

public function actionUpdate( $postID = null ) {
		
		echo $_GET['postID'];
		echo $postID;
		
		
		$model = new PostForm;
		$this->render('update',array(
			'model'=>$model, 				// Model is passed to create.php View!
		));
	}

my CGridView

$this->widget('zii.widgets.grid.CGridView', array(
		'dataProvider'=>$dataProvider,
		'columns'=>array(
			'description',
			array(
				'name'=>'post_time',
				'value'=>'date("M j, Y", strtotime($data->post_time))',
			),
			array(            // display a column with "view", "update" and "delete" buttons
				'class'=>'CButtonColumn',
				'template'=>'{delete}{update}',
				
				'buttons'=>array(
					'update' => array
					(
						'url'=>'CController::createUrl("/post/update", array("postID"=>$data->primaryKey))',
					),
					'delete' => array
					(
						'url'=>'CController::createUrl("/post/delete", array("postID"=>$data->primaryKey))',
					),
				),				
			),
		),
	));