<?php

/**
 *  @link    http://foundationize.com
 *  @package foundationize/yii2-foundation
 *  @version dev
 */

namespace foundationize\foundation;

use Yii;
use yii\helpers\Html;

class FnActiveForm extends \yii\widgets\ActiveForm {

    public $fieldClass = 'foundationize\foundation\FnActiveField';
    public $layout = 'default';

    /**
     * Override default settings for form
     */
    //public $errorCssClass = 'form-error';

    /**
     * @inheritdoc
     */
    public function init() {
        if (!in_array($this->layout, ['default', 'inline'])) {
            throw new InvalidConfigException('Invalid layout type: ' . $this->layout);
        }

        if ($this->layout !== 'default') {
            Html::addCssClass($this->options, 'form-' . $this->layout);
        }
        parent::init();
    }

    /**
     * @inheritdoc
     */
    public function run() {
        parent::run();
        $view = $this->getView();
        ActiveFormAsset::register($view);
    }

}

<?php

/**
 *  @link    http://foundationize.com
 *  @package foundationize/yii2-foundation
 *  @version dev
 */

namespace foundationize\foundation;

use Yii;
use yii\helpers\Html;

class FnActiveForm extends \yii\widgets\ActiveForm {

    public $fieldClass = 'foundationize\foundation\FnActiveField';
    public $layout = 'default';

    /**
     * Override default settings for form
     */
    //public $errorCssClass = 'form-error';

    /**
     * @inheritdoc
     */
    public function init() {
        if (!in_array($this->layout, ['default', 'inline'])) {
            throw new InvalidConfigException('Invalid layout type: ' . $this->layout);
        }

        if ($this->layout !== 'default') {
            Html::addCssClass($this->options, 'form-' . $this->layout);
        }
        parent::init();
    }

    /**
     * @inheritdoc
     */
    public function run() {
        $view = $this->getView();
        ActiveFormAsset::register($view);
        
        return parent::run();
    }

}

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see https://github.com/yiisoft/yii2/blob/2.0.16/framework/UPGRADE.md#upgrade-from-yii-207