getSession()->setFlash('error', 'Alert! Danger alert preview. This alert is dismissable.');
 * ```
 *
 * Multiple messages could be set as follows:
 *
 * ```php
 * \Yii::$app->getSession()->setFlash('error', ['Error 1', 'Error 2']);
 * ```
 *
 * @author Evgeniy Tkachenko 
 */
class Alert extends Widget
{
    /**
     * @var array the alert types configuration for the flash messages.
     * This array is setup as $key => $value, where:
     * - $key is the name of the session flash variable
     * - $value is the array:
     *       - class of alert type (i.e. danger, success, info, warning)
     *       - icon for alert AdminLTE
     */
    public $alertTypes = [
        'error' => [
            'class' => 'alert-danger',
            'icon' => '',
        ],
        'danger' => [
            'class' => 'alert-danger',
            'icon' => '',
        ],
        'success' => [
            'class' => 'alert-success',
            'icon' => '',
        ],
        'info' => [
            'class' => 'alert-info',
            'icon' => '',
        ],
        'warning' => [
            'class' => 'alert-warning',
            'icon' => '',
        ],
    ];
    /**
     * @var array the options for rendering the close button tag.
     */
    public $closeButton = [];
    /**
     * Initializes the widget.
     * This method will register the bootstrap asset bundle. If you override this method,
     * make sure you call the parent implementation first.
     */
    public function init()
    {
        parent::init();
        $session = \Yii::$app->getSession();
        $flashes = $session->getAllFlashes();
        $appendCss = isset($this->options['class']) ? ' ' . $this->options['class'] : '';
        foreach ($flashes as $type => $data) {
            if (isset($this->alertTypes[$type])) {
                $data = (array) $data;
                foreach ($data as $message) {
                    $this->options['class'] = $this->alertTypes[$type]['class'] . $appendCss;
                    $this->options['id'] = $this->getId() . '-' . $type;
                    echo BootstrapAlert::widget([
                            'body' => $this->alertTypes[$type]['icon'] . $message,
                            'closeButton' => $this->closeButton,
                            'options' => $this->options,
                        ]);
                }
                $session->removeFlash($type);
            }
        }
    }
}