I often see that when someone needs something executed on every page request before anything else is executed, they usually put it in the controller beforeAction() method. Things you might want executed on every page request might be, for example (so you know what I’m talking about):

• Handling the layout
• Cleaning all GET and POST parameters (I don’t like to do this but some people do)
• Language handling

I’ve seen people do this with CakePHP as well as with Yii. I find that beforeAction() is actually not an optimal place to put this sort of code. Imagine you put code for all of the examples I gave above plus three more in the beforeAction() method. You might image that the beforeAction() method would become cluttered and hard to read. I prefer lower coupling than this. We want these scripts split up into logical places. And guess what? With Yii this is easy. Application Components!

Let me write an example. Lets say we need to figure out what layout to display to the user on each request. We would like to execute some logic for this before the controller action is called. We do not use beforeFilter(). We instead create an application component. An application component is simply a class that extends CApplicationComponent.

<?php
class LayoutHandler extends CApplicationComponent {
 
	public function init() {
		parent::init();
 
		//Put code here.
 
	}
}

Now everything in the init() method will be executed when this application component is instantiated. So now, we just need to get it to instantiate on every request, before the action is executed. This is done in the application configuration using the preload property.

<?php
// This is the main Web application configuration. Any writable
// CWebApplication properties can be configured here.
return array(
	'basePath'=>dirname(__FILE__).DIRECTORY_SEPARATOR.'..',
 
	// The 'layoutHandler' component will pre-load
	'preload'=>array('layoutHandler'),
 
	// application components
	'components'=>array(
		'layoutHandler'=>array(
			'class'=>'path.to.LayoutHandler',
		),
	),
);

Now there are two main things I have done here:

1. Defined the LayoutHandler class as an application component in the components property
2. Set the layoutHandler to preload with the preload property

You may find that this method is much more organized than simply stuffing code in CController::beforeAction(). It also leaves your code more modular.

Note that now you can even access the LayoutHandler class anywhere within your app via Yii::app()->layoutHandler. Not useful in this example, but this is often very handy.