【WordPress】管理画面に独自の設定画面を追加する方法｜add_menu_pageの基本と応用

add_menu_page(
  string $page_title,
  string $menu_title,
  string $capability,
  string $menu_slug,
  callable $function,
  string $icon_url = '',
  int $position = null
);

add_action('admin_menu', 'my_custom_settings_menu');
function my_custom_settings_menu() {
  add_menu_page(
    'サイト設定',
    'サイト設定',
    'manage_options',
    'my-site-settings',
    'my_site_settings_page',
    'dashicons-admin-generic',
    60
  );
}

function my_site_settings_page() {
  echo '<div class="wrap">';
  echo '<h1>サイト設定</h1>';
  settings_errors(); // 保存後の「設定を保存しました」メッセージを表示
  echo '<form method="post" action="options.php">';
  settings_fields('my_settings_group');
  do_settings_sections('my-site-settings');
  submit_button();
  echo '</form>';
  echo '</div>';
}

add_action('admin_init', 'my_settings_init');
function my_settings_init() {
  register_setting('my_settings_group', 'my_option_text', array(
    'sanitize_callback' => 'sanitize_text_field',
  ));

  add_settings_section(
    'my_settings_section',
    '基本設定',
    null,
    'my-site-settings'
  );

  add_settings_field(
    'my_option_text',
    'テキスト設定',
    'my_option_text_callback',
    'my-site-settings',
    'my_settings_section'
  );
}

function my_option_text_callback() {
  $value = get_option('my_option_text', '');
  echo '<input type="text" name="my_option_text" value="' . esc_attr($value) . '" />';
}

$text = get_option('my_option_text');
echo esc_html($text);