How is the <can_be_empty> tag handled for a multiselect form element?

dmitry_fedyuk (Dmitrii Fediuk) May 13, 2016, 2:31pm 1

A usage example

github.com

magento/magento2/blob/ffea3cd/app/code/Magento/Backend/etc/adminhtml/system.xml#L201-L205


<field id="allow" translate="label" type="multiselect" sortOrder="2" showInDefault="1" showInWebsite="1" showInStore="1">
    <label>Allow Countries</label>
    <source_model>Magento\Directory\Model\Config\Source\Country</source_model>
    <can_be_empty>1</can_be_empty>
</field>

How is it handled?

\Magento\Config/\Block\System\Config\Form::getElementHtml()

github.com

magento/magento2/blob/ffea3cd/app/code/Magento/Config/Block/System/Config/Form.php#L372-L374


if ($field->getType() == 'multiselect') {
    $formField->setCanBeEmpty($field->canBeEmpty());
}

\Magento\Framework\Data\Form\Element\Multiselect::getElementHtml()

github.com

magento/magento2/blob/ffea3cd/lib/internal/Magento/Framework/Data/Form/Element/Multiselect.php#L59-L61


if ($this->getCanBeEmpty()) {
    $html .= '<input type="hidden" name="' . parent::getName() . '" value="" />';
}