Basic concepts of Yii ===================== Component and Object -------------------- Classes of the Yii framework usually extend from one of the two base classes [[Object]] and [[Component]]. These classes provide useful features that are added automatically to all classes extending from them. The `Object` class provides the [configuration and property feature](../api/base/Object.md). The `Component` class extends from `Object` and adds [event handling](events.md) and [behaviors](behaviors.md). `Object` is usually used for classes that represent basic data structures while `Component` is used for application components and other classes that implement higher logic. Object Configuration -------------------- The [[Object]] class introduces a uniform way of configuring objects. Any descendant class of [[Object]] should declare its constructor (if needed) in the following way so that it can be properly configured: ```php class MyClass extends \yii\base\Object { public function __construct($param1, $param2, $config = []) { // ... initialization before configuration is applied parent::__construct($config); } public function init() { parent::init(); // ... initialization after configuration is applied } } ``` In the above, the last parameter of the constructor must take a configuration array which contains name-value pairs for initializing the properties at the end of the constructor. You can override the `init()` method to do initialization work that should be done after the configuration is applied. By following this convention, you will be able to create and configure a new object using a configuration array like the following: ```php $object = Yii::createObject([ 'class' => 'MyClass', 'property1' => 'abc', 'property2' => 'cde', ], $param1, $param2); ``` Path Aliases ------------ Yii 2.0 expands the usage of path aliases to both file/directory paths and URLs. An alias must start with a `@` character so that it can be differentiated from file/directory paths and URLs. For example, the alias `@yii` refers to the Yii installation directory while `@web` contains base URL for currently running web application. Path aliases are supported in most places in the Yii core code. For example, `FileCache::cachePath` can take both a path alias and a normal directory path. Path alias is also closely related with class namespaces. It is recommended that a path alias be defined for each root namespace so that you can use Yii the class autoloader without any further configuration. For example, because `@yii` refers to the Yii installation directory, a class like `yii\web\Request` can be autoloaded by Yii. If you use a third party library such as Zend Framework, you may define a path alias `@Zend` which refers to its installation directory and Yii will be able to autoload any class in this library. Autoloading ----------- TBD Helper classes -------------- TDB