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123 lines
4.2 KiB
Markdown
123 lines
4.2 KiB
Markdown
Basic concepts of Yii
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=====================
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Component and Object
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--------------------
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Classes of the Yii framework usually extend from one of the two base classes [[yii\base\Object]] and [[yii\base\Component]].
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These classes provide useful features that are added automatically to all classes extending from them.
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The [[yii\base\Object|Object]] class provides the [configuration and property feature](../api/base/Object.md).
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The [[yii\base\Component|Component]] class extends from [[yii\base\Object|Object]] and adds
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[event handling](events.md) and [behaviors](behaviors.md).
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[[yii\base\Object|Object]] is usually used for classes that represent basic data structures while
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[[yii\base\Component|Component]] is used for application components and other classes that implement higher logic.
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Object Configuration
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--------------------
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The [[yii\base\Object|Object]] class introduces a uniform way of configuring objects. Any descendant class
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of [[yii\base\Object|Object]] should declare its constructor (if needed) in the following way so that
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it can be properly configured:
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```php
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class MyClass extends \yii\base\Object
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{
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public function __construct($param1, $param2, $config = [])
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{
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// ... initialization before configuration is applied
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parent::__construct($config);
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}
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public function init()
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{
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parent::init();
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// ... initialization after configuration is applied
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}
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}
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```
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In the above, the last parameter of the constructor must take a configuration array
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which contains name-value pairs for initializing the properties at the end of the constructor.
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You can override the `init()` method to do initialization work that should be done after
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the configuration is applied.
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By following this convention, you will be able to create and configure a new object
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using a configuration array like the following:
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```php
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$object = Yii::createObject([
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'class' => 'MyClass',
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'property1' => 'abc',
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'property2' => 'cde',
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], $param1, $param2);
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```
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Path Aliases
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------------
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Yii 2.0 expands the usage of path aliases to both file/directory paths and URLs. An alias
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must start with a `@` character so that it can be differentiated from file/directory paths and URLs.
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For example, the alias `@yii` refers to the Yii installation directory while `@web` contains base URL for currently
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running web application. Path aliases are supported in most places in the Yii core code. For example,
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`FileCache::cachePath` can take both a path alias and a normal directory path.
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Path alias is also closely related with class namespaces. It is recommended that a path
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alias be defined for each root namespace so that you can use Yii the class autoloader without
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any further configuration. For example, because `@yii` refers to the Yii installation directory,
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a class like `yii\web\Request` can be autoloaded by Yii. If you use a third party library
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such as Zend Framework, you may define a path alias `@Zend` which refers to its installation
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directory and Yii will be able to autoload any class in this library.
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Autoloading
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-----------
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All classes, interfaces and traits are loaded automatically at the moment they are used. There's no need to use
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`include` or `require`. It is, as well, true for Composer-loaded packages and Yii extensions.
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Autoloader works according to [PSR-4](https://github.com/php-fig/fig-standards/blob/master/proposed/psr-4-autoloader/psr-4-autoloader.md).
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That means namespaces and class, interface and trait names should correspond to file system paths except root namespace
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path that is defined by an alias.
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For example, if standard alias `@app` refers to `/var/www/example.com/` then `\app\models\User` will be loaded from
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`/var/www/example.com/app/models/User.php`.
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Custom alias may be added using the following code:
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```php
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Yii::setAlias('@shared', realpath('~/src/shared'));
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```
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Additional autoloaders may be registered using standard PHP `spl_autoload_register`.
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Helper classes
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--------------
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Helper class typically contains static methods only and used as follows:
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```php
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use \yii\helpers\Html;
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echo Html::encode('Test > test');
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```
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There are several classes provided by framework:
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- ArrayHelper
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- Console
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- FileHelper
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- Html
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- HtmlPurifier
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- Inflector
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- Json
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- Markdown
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- Security
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- StringHelper
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- VarDumper
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