[WordPress]

00-addMenuPage.php

<?php

public function addMenuPage()
{
    add_menu_page(
      'Acme Menu',
      'Acme Menu',
      'manage_options',
      'acme-custom-menu',
      array($this, 'display'),
      'dashicons-dashboard',
      30
    );

    add_submenu_page(
      'acme-custom-menu',
      'Acme Menu',
      'Acme Menu',
      'Acme Menu',
      'acme-custom-menu',
      array($this, 'display')
    );
}

01-display.php

<?php

public function display()
{
    include_once $this->pluginPath . 'views/acme-settings.php';
}

02-acme-settings.php

<?php
/**
 * Renders the settings page for the plugin.
 */
?>
<div class="wrap">
    <h1 class="wp-heading-inline"><?php echo get_admin_page_title(); ?></h1>
    <?php if ($this->showSuccessMessage()) { ?>
      <?php include_once 'partials/settings-saved.php'; ?>
    ?>
    <div id="acme-settings-schedule">
        <form id="acme-form" method="post" action="<?php echo esc_html(admin_url('admin-post.php')); ?>"">
            <!-- This is where your settings go. -->
            <p>
                <?php
                submit_button(
                    'Save',
                    'primary',
                    'acme-save-settings',
                    false
                );
                wp_nonce_field(
                    'acme-save',
                    'acme-save-nonce'
                );
                ?>
            </p>
        </form>
    </div>
</div>
                                      

03-showSuccessMessage.php

<?php

public function showSuccessMessage()
{
  return (false !== get_option('acme_custom_setting'));
}

04-settings-saved.php

<?php
/**
 * Renders the success message if the option has been properly saved.
 */
?>

<div class="notice-success notice is-dismissible">
    <p>Your settings have been successfully saved.</p>
    <button type="button" class="notice-dismiss">
        <span class="screen-reader-text">Dismiss this notice.</span>
    </button>
</div>