Magento 2 - How to create a custom module with admin config?

Question

How could I create a simple module to Magento 2 with admin configuration, like Porto theme or Amasty modules?

Store > Configuration

Answer 1

In Your Custome Module system.xml looks like This

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Config:etc/system_file.xsd">
    <system>
        <tab id="yourid" translate="label" sortOrder="10">
            <label>YourModuleName</label>
        </tab>
        <section id="helloworld" translate="label" sortOrder="130" showInDefault="1" showInWebsite="1" showInStore="1">
            <class>separator-top</class>
            <label>Your Tab Label</label>
            <tab>tabname</tab>
            <resource>your_modulename::yourmodule_configuration</resource>
            <group id="general" translate="label" type="text" sortOrder="10" showInDefault="1" showInWebsite="0" showInStore="0">
                <label>General Configuration</label>
                <field id="enable" translate="label" type="select" sortOrder="1" showInDefault="1" showInWebsite="0" showInStore="0">
                    <label>Module Enable</label>
                    <source_model>Magento\Config\Model\Config\Source\Yesno</source_model>
                </field>
                <field id="display_text" translate="label" type="text" sortOrder="1" showInDefault="1" showInWebsite="0" showInStore="0">
                    <label>Display Text</label>
                    <comment>This text will display on the frontend.</comment>
                </field>
            </group>
        </section>
    </system>
</config>

Flush Magento Cache

bin/magento cache:flush

Getting Values Of Configuration

Create Helper Class

<?php

namespace Your\namespace\Helper;

use Magento\Framework\App\Helper\AbstractHelper;
use Magento\Store\Model\StoreManagerInterface;
use Magento\Framework\ObjectManagerInterface;
use Magento\Framework\App\Helper\Context;
use Magento\Store\Model\ScopeInterface;

class Data extends AbstractHelper
{
    protected $storeManager;
    protected $objectManager;

    const XML_PATH_HELLOWORLD = 'helloworld/';



    public function __construct(Context $context,
        ObjectManagerInterface $objectManager,
        StoreManagerInterface $storeManager
    ) {
        $this->objectManager = $objectManager;
        $this->storeManager  = $storeManager;
        parent::__construct($context);
    }

    public function getConfigValue($field, $storeId = null)
    {
        return $this->scopeConfig->getValue(
            $field, ScopeInterface::SCOPE_STORE, $storeId
        );
    }


    public function getGeneralConfig($code, $storeId = null)
    {
        return $this->getConfigValue(self::XML_PATH_HELLOWORLD . $code, $storeId);
    }


}

Getting Values Of Configuration Using Helper Class

$helper = $this->objectManager->create('Your\namespace\Helper\Data');
echo $helper->getGeneralConfig('enable');
echo $helper->getGeneralConfig('display_text');

Magento2 system.xml provides below fields type

checkbox,
checkboxes,
column,
date,
editablemultiselect,
editor,
fieldset,
file,
gallery,
hidden,
image,
imagefile,
label,
link,
multiline,
multiselect,
note,
obscure,
password,
radio,
radios,
reset,
select,
submit,
text,
textarea,
time

You Can Find More About system.xml Here

Answer 2

When you have to make configuration in admin you have to make a system.xml in your module's etc/adminhtml and a config.xml to define their default values.

You can read more on this in this tutorial..

Answer 3

I was having hard time using

return $this->scopeConfig->getValue($field, ScopeInterface::SCOPE_STORE,$storeId);

in my helper that extended AbstractHelper.

Was getting error in

/var/log/httpd/error_log.log

PHP Fatal error:  Uncaught Error: Call to a member function getValue() on null in /var/www/html/myproject/app/code/My/Customer/Helper/Data.php:170

Until I used the following

 $objectManager = \Magento\Framework\App\ObjectManager::getInstance();
 $val = $objectManager->get('Magento\Framework\App\Config\ScopeConfigInterface')->getValue($config_path);

where $config_path was something like dev/debug/template_hints

Hope this helps someone like me.