[Yii Framework] How to embed the css and images in a module

Maybe there is not a good introduction about how to embed css and images in a module in the forum (or cookbook) of Yii framework, but thanks to Qiang, who builds the great framework, that I found the way in the kernal code in framework/gii (In fact that gii is a module!)

Here is the structure of my module "admin"

| | |~modules/
| | | `~admin/
| | |   |~assets/
| | |   | |+css/
| | |   | |+images/
| | |   |+components/
| | |   |+controllers/
| | |   |+messages/
| | |   |+models/
| | |   |+views/
| | |   `-AdminModule.php*

1. Modify the AdminModule.php, add the code as below:

private $_assetsUrl;

/**
* @return string the base URL that contains all published asset files of this module.
*/
public function getAssetsUrl()
{
    if($this->_assetsUrl===null)
        $this->_assetsUrl=Yii::app()->getAssetManager()->publish(Yii::getPathOfAlias('admin.assets'));
        return $this->_assetsUrl;
}

/**
 * @param string the base URL that contains all published asset files of this module.
 */
public function setAssetsUrl($value)
{
    $this->_assetsUrl=$value;
}

public function registerCss($file, $media='all')
{
    $href = $this->getAssetsUrl().'/css/'.$file;
    return '<link rel="stylesheet" type="text/css" href="'.$href.'" media="'.$media.'" />';
}

public function registerImage($file)
{
    return $this->getAssetsUrl().'/images/'.$file;
}

2. Example of calling the css and images in modules/admin/layouts/main.php

//calling the css
<?php echo Yii::app()->controller->module->registerCss('main.css');?>

//calling the images
<?php echo CHtml::image(Yii::app()->controller->module->registerImage('logo.png'), "logo");?>

Have fun with Yii!