Behaviors & events

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These features provide endless possibilities and unbelievable flexibility, but as current documentation does not give more than a few examples, it might be difficult to fully understand their internals and requirements.

It should be noted that they do mostly the same thing. You can attach behaviors and event handlers to components to modify the components' behavior.

It is useful when you want to interrupt the normal application flow without extending base classes.

For example, enabling gzip compression on the output could be done via extending CWebApplication. But because there are entry points for event handlers, one can do this:

Yii::app()->onbeginRequest = create_function('$event', 'return ob_start("ob_gzhandler");'),
Yii::app()->onendRequest = create_function('$event', 'return ob_end_flush();'),

You can create an event handler -- which is simply a method in some class with a specific signature -- and attach it to the event of an object. You can add as many event handlers as you wish, from as many objects as you wish. If the event handler is, effectively static, then you can create the object as you assign it:

$test_comp->onSomethingGoesOn = array(new SomeClass, 'eventHandler1');
$test_comp->onSomethingGoesOn = array(new SomeOtherClass, 'eventHandler2');
$test_comp->onSomethingGoesOn = array(new YetAnotherClass, 'eventHandler3');

As long as you have a handle on the object, then you can add an event handler to it.

At some point, you can then raise the event with something like one of these:

$test_comp->onSomethingGoesOn(new CEvent($this));
$test_comp->onSomethingGoesOn(new CEvent());

So, basically, it allows you build a list of function calls that can later be executed, in the order they were added. It can save you passing around a lot of object refs and building conditional code, since you can still raise the event, even if it doesn't do anything.

Behaviors are simply a way of adding methods to an object. In an OO language like Ruby, it's quite possible to start with an completely empty object and simply build its behavior as you go along. Yii provides this behavior with a little magic. The key is that the class you wish to add the behavior from must extend Cbehavior.

class SomeClass extends CBehavior
{
    public function add($x, $y) { return $x + $y; }
}

Then use with:

$test_comp = new TestComponent(); 
$test_comp->attachbehavior('blah', new SomeClass);
$test_comp->add(2, 5);

So, in this case, you are extending the functionality of an object with functionality of another object.

After studying this cookbook page it is encouraged to reread the corresponding guide page as it contains advanced information (for example, if you are familiar with interfaces, you might find it enough to implement IBehavior before extending CBehavior).

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Written by: pestaa
Last updated by: Gismo
Created on: Aug 24, 2009
Last updated: 5 years ago
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