WordPress Widgets

wp-functions-widget-init.php

<?php
/**
 * Register widget area. Twenty Fiften Theme
 * In functions.php file
 *
 * @link https://codex.wordpress.org/Function_Reference/register_sidebar
 */
function twentyfifteen_widgets_init() {
	register_sidebar( array(
		'name'          => __( 'Widget Area', 'twentyfifteen' ),
		'id'            => 'sidebar-1',
		'description'   => __( 'Add widgets here to appear in your sidebar.', 'twentyfifteen' ),
		'before_widget' => '<aside id="%1$s" class="widget %2$s">',
		'after_widget'  => '</aside>',
		'before_title'  => '<h2 class="widget-title">',
		'after_title'   => '</h2>',
	) );
}
add_action( 'widgets_init', 'twentyfifteen_widgets_init' );

wp-twentyfifteen-after-setup-theme.php

<?php

if ( ! function_exists( 'twentyfifteen_setup' ) ) :
/**
 * Sets up theme defaults and registers support for various WordPress features.
 *
 * Note that this function is hooked into the after_setup_theme hook, which
 * runs before the init hook. The init hook is too late for some features, such
 * as indicating support for post thumbnails.
 *
 * @since Twenty Fifteen 1.0
 */
function twentyfifteen_setup() {

	/*
	 * Make theme available for translation.
	 * Translations can be filed in the /languages/ directory.
	 * If you're building a theme based on twentyfifteen, use a find and replace
	 * to change 'twentyfifteen' to the name of your theme in all the template files
	 */
	load_theme_textdomain( 'twentyfifteen', get_template_directory() . '/languages' );

	// Add default posts and comments RSS feed links to head.
	add_theme_support( 'automatic-feed-links' );

	/*
	 * Let WordPress manage the document title.
	 * By adding theme support, we declare that this theme does not use a
	 * hard-coded <title> tag in the document head, and expect WordPress to
	 * provide it for us.
	 */
	add_theme_support( 'title-tag' );

	/*
	 * Enable support for Post Thumbnails on posts and pages.
	 *
	 * See: https://codex.wordpress.org/Function_Reference/add_theme_support#Post_Thumbnails
	 */
	add_theme_support( 'post-thumbnails' );
	set_post_thumbnail_size( 825, 510, true );

	// This theme uses wp_nav_menu() in two locations.
	register_nav_menus( array(
		'primary' => __( 'Primary Menu',      'twentyfifteen' ),
		'social'  => __( 'Social Links Menu', 'twentyfifteen' ),
	) );

	/*
	 * Switch default core markup for search form, comment form, and comments
	 * to output valid HTML5.
	 */
	add_theme_support( 'html5', array(
		'search-form', 'comment-form', 'comment-list', 'gallery', 'caption'
	) );

	/*
	 * Enable support for Post Formats.
	 *
	 * See: https://codex.wordpress.org/Post_Formats
	 */
	add_theme_support( 'post-formats', array(
		'aside', 'image', 'video', 'quote', 'link', 'gallery', 'status', 'audio', 'chat'
	) );

	/*
	 * Enable support for custom logo.
	 *
	 * @since Twenty Fifteen 1.5
	 */
	add_theme_support( 'custom-logo', array(
		'height'      => 248,
		'width'       => 248,
		'flex-height' => true,
	) );

	$color_scheme  = twentyfifteen_get_color_scheme();
	$default_color = trim( $color_scheme[0], '#' );

	// Setup the WordPress core custom background feature.
	add_theme_support( 'custom-background', apply_filters( 'twentyfifteen_custom_background_args', array(
		'default-color'      => $default_color,
		'default-attachment' => 'fixed',
	) ) );

	/*
	 * This theme styles the visual editor to resemble the theme style,
	 * specifically font, colors, icons, and column width.
	 */
	add_editor_style( array( 'css/editor-style.css', 'genericons/genericons.css', twentyfifteen_fonts_url() ) );

	// Indicate widget sidebars can use selective refresh in the Customizer.
	add_theme_support( 'customize-selective-refresh-widgets' );
}
endif; // twentyfifteen_setup
add_action( 'after_setup_theme', 'twentyfifteen_setup' );

wp-twentyfifteen-theme-sidebar.php

<?php
/**
 * The sidebar containing the main widget area
 *
 * @package WordPress
 * @subpackage Twenty_Fifteen
 * @since Twenty Fifteen 1.0
 */

if ( has_nav_menu( 'primary' ) || has_nav_menu( 'social' ) || is_active_sidebar( 'sidebar-1' )  ) : ?>
	<div id="secondary" class="secondary">

		<?php if ( has_nav_menu( 'primary' ) ) : ?>
			<nav id="site-navigation" class="main-navigation" role="navigation">
				<?php
					// Primary navigation menu.
					wp_nav_menu( array(
						'menu_class'     => 'nav-menu',
						'theme_location' => 'primary',
					) );
				?>
			</nav><!-- .main-navigation -->
		<?php endif; ?>

		<?php if ( has_nav_menu( 'social' ) ) : ?>
			<nav id="social-navigation" class="social-navigation" role="navigation">
				<?php
					// Social links navigation menu.
					wp_nav_menu( array(
						'theme_location' => 'social',
						'depth'          => 1,
						'link_before'    => '<span class="screen-reader-text">',
						'link_after'     => '</span>',
					) );
				?>
			</nav><!-- .social-navigation -->
		<?php endif; ?>

		<?php if ( is_active_sidebar( 'sidebar-1' ) ) : ?>
			<div id="widget-area" class="widget-area" role="complementary">
				<?php dynamic_sidebar( 'sidebar-1' ); ?>
			</div><!-- .widget-area -->
		<?php endif; ?>

	</div><!-- .secondary -->

<?php endif; ?>

wp-twentyfifteen-wp-nav-menu-use.php

<?php if ( has_nav_menu( 'primary' ) ) : ?>
	<nav id="site-navigation" class="main-navigation" role="navigation">
		<?php
			// Primary navigation menu.
			wp_nav_menu( array(
				'menu_class'     => 'nav-menu',
				'theme_location' => 'primary',
			) );
		?>
	</nav><!-- .main-navigation -->
<?php endif; ?>

<?php if ( has_nav_menu( 'social' ) ) : ?>
	<nav id="social-navigation" class="social-navigation" role="navigation">
		<?php
			// Social links navigation menu.
			wp_nav_menu( array(
				'theme_location' => 'social',
				'depth'          => 1,
				'link_before'    => '<span class="screen-reader-text">',
				'link_after'     => '</span>',
			) );
		?>
	</nav><!-- .social-navigation -->
<?php endif; ?>