yii2-bootstrap/docs/guide/basics.md

Basic concepts of Yii

Component and Object

Yii 2.0 breaks the CComponent class in 1.1 into two classes: Object and Component. The Object class is a lightweight base class that allows defining class properties via getters and setters. The Component class extends from Object and supports the event feature and the behavior feature.

If your class does not need the event or behavior feature, you should consider using Object as the base class. This is usually the case for classes that represent basic data structures.

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:

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:

$object = Yii::createObject([
    'class' => 'MyClass',
    'property1' => 'abc',
    'property2' => 'cde',
], $param1, $param2);

More on configuration in configuration

Path Alias

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. 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