O Guia Definitivo do Yii 1.1

• An extension should be self-contained. That is, its external dependency should be
minimal. It would be a headache for its users if an extension requires installation of
additional packages, classes or resource files.
• Files belonging to an extension should be organized under the same directory whose
name is the extension name
• Classes in an extension should be prefixed with some letter(s) to avoid naming
conflict with classes in other extensions.
• An extension should come with detailed installation and API documentation. This
would reduce the time and effort needed by other developers when they use the
extension.
• An extension should be using an appropriate license. If you want to make your
extension to be used by both open-source and closed-source projects, you may
consider using licenses such as BSD, MIT, etc., but not GPL as it requires its derived
code to be open-source as well.
In the following, we describe how to create a new extension, according to its categorization
as described in overview. These descriptions also apply when you are creating a
component mainly used in your own projects.
Application Component
An application component should implement the interface [IApplicationComponent] or
extend from CApplicationComponent. The main method needed to be implemented is
[IApplicationComponent::init] in which the component performs some initialization work.
This method is invoked after the component is created and the initial property values
(specified in application configuration) are applied.
By default, an application component is created and initialized only when it is accessed for
the first time during request handling. If an application component needs to be created
right after the application instance is created, it should require the user to list its ID in the
CApplication::preload property.
Behavior
To create a behavior, one must implement the [IBehavior] interface. For convenience, Yii
provides a base class CBehavior that already implements this interface and provides some
additional convenient methods. Child classes mainly need to implement the extra methods
that they intend to make available to the components being attached to.
When developing behaviors for CModel and CActiveRecord, one can also extend
CModelBehavior and CActiveRecordBehavior, respectively. These base classes offer
additional features that are specifically made for CModel and CActiveRecord. For
example, the CActiveRecordBehavior class implements a set of methods to respond to the
life cycle events raised in an ActiveRecord object. A child class can thus override these
methods to put in customized code which will participate in the AR life cycles.
The following code shows an example of an ActiveRecord behavior. When this behavior is
attached to an AR object and when the AR object is being saved by calling save(), it will
automatically sets the create_timeand update_time attributes with the current timestamp.