magento 2 system configuration hide fields if some values are not set

Question

basically i want to show configuration fields only if value is set. since other fields require first value in order to call external source.

<field id="database" showInDefault="1" showInStore="1" showInWebsite="1" sortOrder="2" translate="label" type="select">
    <label>Database</label>
    <comment>choose database</comment>
    <source_model>Wemessage\ModuleX\Model\Config\Source\Database\Source</source_model>
    <frontend_model>Wemessage\ModuleX\Model\Config\Source\Database\Model</frontend_model>   
</field>

if i remove frontend_model i do see my field in configuration, if i add it back the configuration page is empty.

this is my frontend model file:

namespace Wemessage\ModuleX\Model\Config\Source\Database\Model;

use Wemessage\ModuleX\Helper\Data;

class Model extends \Magento\Config\Block\System\Config\Form\Field 
{
    /**
     * Render fieldset html
     *
     * @param \Magento\Framework\Data\Form\Element\AbstractElement $element
     * @return string
     */
    public function render(\Magento\Framework\Data\Form\Element\AbstractElement $element)
    {
        $html = '';
        //$helper = new Data();
        //$token = $helper->getConfigValue('module/api/token');
        if($token){
            $html .= parent::render($element);
        }
        return $html;
    }
}

any idea what can be wrong here ?

Answer 1

After trial and error solved my problem:

public function render(AbstractElement $element)
{
    $html = '';
    $token = $this->dataHelper->getConfigValue('module/api/token');
    if($token){
        return parent::render($element);
    } else {
        return $this->_decorateRowHtml($element, $html);
    }
}

public function _decorateRowHtml($element, $html)
{
    return '<tr id="row_' . $element->getHtmlId() . '">' . $html . '</tr>';
}