Note: This section is under development.

Yii provides many classes that help simplify common coding tasks, such as string or array manipulations, HTML code generation, and so on. These helper classes are organized under the yii\helpers namespace and are all static classes (meaning they contain only static properties and methods and should not be instantiated).

You use a helper class by directly calling one of its static methods, like the following:

use yii\helpers\Html;

echo Html::encode('Test > test');

Note: To support customizing helper classes, Yii breaks each core helper class into two classes: a base class (e.g. BaseArrayHelper) and a concrete class (e.g. ArrayHelper). When you use a helper, you should only use the concrete version and never use the base class.

Core Helper Classes

The following core helper classes are provided in the Yii releases:

  • ArrayHelper
  • Console
  • FileHelper
  • FormatConverter
  • Html
  • HtmlPurifier
  • Imagine (provided by yii2-imagine extension)
  • Inflector
  • Json
  • Markdown
  • StringHelper
  • Url
  • VarDumper

Customizing Helper Classes

To customize a core helper class (e.g. yii\helpers\ArrayHelper), you should create a new class extending from the helpers corresponding base class (e.g. yii\helpers\BaseArrayHelper) and name your class the same as the corresponding concrete class (e.g. yii\helpers\ArrayHelper), including its namespace. This class will then be set up to replace the original implementation of the framework.

The following example shows how to customize the merge() method of the yii\helpers\ArrayHelper class:


namespace yii\helpers;

class ArrayHelper extends BaseArrayHelper
    public static function merge($a, $b)
        // your custom implementation

Save your class in a file named ArrayHelper.php. The file can be in any directory, for example @app/components.

Next, in your application's entry script, add the following line of code after including the yii.php file to tell the Yii class autoloader to load your custom class instead of the original helper class from the framework:

Yii::$classMap['yii\helpers\ArrayHelper'] = '@app/components/ArrayHelper.php';

Note that customizing of helper classes is only useful if you want to change the behavior of an existing function of the helpers. If you want to add additional functions to use in your application you may better create a separate helper for that.