Creating a custom form and saving configuration changes

In this recipe, we will create a form that allows saving the company name and phone number for the website to the configuration. Forms are defined as classes that implement \Drupal\Core\Form\FormInterface. \Drupal\Core\Form\FormBase serves as a standard base class for forms. We will extend this class to create a new form that saves the custom configuration.

How to do it…

1. First, we need to create the src/Form directory in the module’s directory. We will put our form class in this directory, which gives our form class the Form namespace:

   mkdir -p src/Form

2. Create a file named CompanyForm.php in the Form directory. This will hold our CompanyForm form class.
3. Our CompanyForm class will extend the FormBase class provided by Drupal core:

   <?php

   namespace Drupal\mymodule\Form;

   use Drupal\Core\Form\FormBase;

   use Drupal\Core\Form\FormStateInterface;

   class CompanyForm extends FormBase {

     public function...