Change the config value based on dropdown change in magento 2.4.2

Question

I am using Magento Open Source Edition 2.4.2. I have a custom module where I have an admin configuration like below which is under 'Stores > Custom Menu'.

In the system.xml, I have added the backend model for the 'dropdown field - Import Custom Data' as 'Vendor\Module\Model\Config\Backend\SetTimestamp'

Here is my 'SetTimestamp.php file':

/**
     * @param \Magento\Framework\Model\Context $context
     * @param \Magento\Framework\Registry $registry
     * @param \Magento\Framework\App\Config\ScopeConfigInterface $config
     * @param \Magento\Framework\App\Cache\TypeListInterface $cacheTypeList
     * @param WriterInterface $configWriter
     * @param \Magento\Framework\Model\ResourceModel\AbstractResource $resource
     * @param \Magento\Framework\Data\Collection\AbstractDb $resourceCollection
     * @param array $data
     */
    public function __construct(
        \Magento\Framework\Model\Context $context,
        \Magento\Framework\Registry $registry,
        \Magento\Framework\App\Config\ScopeConfigInterface $config,
        \Magento\Framework\App\Cache\TypeListInterface $cacheTypeList,
        WriterInterface $configWriter,
        \Magento\Framework\Model\ResourceModel\AbstractResource $resource = null,
        \Magento\Framework\Data\Collection\AbstractDb $resourceCollection = null,
        array $data = []
    ) {
        $this->configWriter = $configWriter;
        parent::__construct($context, $registry, $config, $cacheTypeList, $resource, $resourceCollection, $data);
    }

    /**
     * Change the Timestamp value to 0 if the Import Customer option gets changed
     *
     * @return $this
     */
    public function afterSave()
    {
        $scope = $this->getData('scope');
        $scopeId = $this->getData('scope_id');

        if ($this->isValueChanged()) {
            $this->configWriter->save(
                self::TIMESTAMP_VALUE_FIELD,
                0,
                $scope,
                $scopeId
            );
        }

        return parent::afterSave();
    }

But, this code doesn't set the value '0' instead it still has the long timestamp value.

Can anyone please help?

Answer 1

Give a try with following.

Field xml code would be part of adminhtml/system.xml

<field id="timestamp" translate="label" type="text" sortOrder="1" showInDefault="1" showInWebsite="0" showInStore="0">
        <label>SetTimestamp</label>
        <comment>SetTimestamp</comment>
       <backend_model>Vendor\Model\Config\Backend\SetTimestamp</backend_model>
</field>

File: Vendor\MostSold\Model\Config\Backend\SetTimestamp.php

<?php

namespace Vendor\Module\Model\Config\Backend;

/**
 * Class SetTimestamp
 * @package Vendor\Module\Model\Config\Backend
 */
class SetTimestamp extends \Magento\Framework\App\Config\Value
{
    /**
     * @return SetTimestamp
     */
    public function beforeSave()
    {
        $value = $this->getValue();

        if ($this->isValueChanged() && $value !== '0') {
            $this->setValue(0);
        }
        return parent::beforeSave();
    }
}