WordPress函数：get_body_class body元素的应有的class

函数原型：

get_body_class( string|string[] $css_class = '' ): string[]

参数说明：

$css_class 空格分割的字符串或者字符串数组，表示要添加到 body 元素的 class。

返回结果是 class 数组。

函数源码：

function get_body_class( $css_class = '' ) {
	global $wp_query;

	$classes = array();

	if ( is_rtl() ) {
		$classes[] = 'rtl';
	}

	if ( is_front_page() ) {
		$classes[] = 'home';
	}
	if ( is_home() ) {
		$classes[] = 'blog';
	}
	if ( is_privacy_policy() ) {
		$classes[] = 'privacy-policy';
	}
	if ( is_archive() ) {
		$classes[] = 'archive';
	}
	if ( is_date() ) {
		$classes[] = 'date';
	}
	if ( is_search() ) {
		$classes[] = 'search';
		$classes[] = $wp_query->posts ? 'search-results' : 'search-no-results';
	}
	if ( is_paged() ) {
		$classes[] = 'paged';
	}
	if ( is_attachment() ) {
		$classes[] = 'attachment';
	}
	if ( is_404() ) {
		$classes[] = 'error404';
	}

	if ( is_singular() ) {
		$post_id   = $wp_query->get_queried_object_id();
		$post      = $wp_query->get_queried_object();
		$post_type = $post->post_type;

		if ( is_page_template() ) {
			$classes[] = "{$post_type}-template";

			$template_slug  = get_page_template_slug( $post_id );
			$template_parts = explode( '/', $template_slug );

			foreach ( $template_parts as $part ) {
				$classes[] = "{$post_type}-template-" . sanitize_html_class( str_replace( array( '.', '/' ), '-', basename( $part, '.php' ) ) );
			}
			$classes[] = "{$post_type}-template-" . sanitize_html_class( str_replace( '.', '-', $template_slug ) );
		} else {
			$classes[] = "{$post_type}-template-default";
		}

		if ( is_single() ) {
			$classes[] = 'single';
			if ( isset( $post->post_type ) ) {
				$classes[] = 'single-' . sanitize_html_class( $post->post_type, $post_id );
				$classes[] = 'postid-' . $post_id;

				// Post Format.
				if ( post_type_supports( $post->post_type, 'post-formats' ) ) {
					$post_format = get_post_format( $post->ID );

					if ( $post_format && ! is_wp_error( $post_format ) ) {
						$classes[] = 'single-format-' . sanitize_html_class( $post_format );
					} else {
						$classes[] = 'single-format-standard';
					}
				}
			}
		}

		if ( is_attachment() ) {
			$mime_type   = get_post_mime_type( $post_id );
			$mime_prefix = array( 'application/', 'image/', 'text/', 'audio/', 'video/', 'music/' );
			$classes[]   = 'attachmentid-' . $post_id;
			$classes[]   = 'attachment-' . str_replace( $mime_prefix, '', $mime_type );
		} elseif ( is_page() ) {
			$classes[] = 'page';

			$page_id = $wp_query->get_queried_object_id();

			$post = get_post( $page_id );

			$classes[] = 'page-id-' . $page_id;

			if ( get_pages(
				array(
					'parent' => $page_id,
					'number' => 1,
				)
			) ) {
				$classes[] = 'page-parent';
			}

			if ( $post->post_parent ) {
				$classes[] = 'page-child';
				$classes[] = 'parent-pageid-' . $post->post_parent;
			}
		}
	} elseif ( is_archive() ) {
		if ( is_post_type_archive() ) {
			$classes[] = 'post-type-archive';
			$post_type = get_query_var( 'post_type' );
			if ( is_array( $post_type ) ) {
				$post_type = reset( $post_type );
			}
			$classes[] = 'post-type-archive-' . sanitize_html_class( $post_type );
		} elseif ( is_author() ) {
			$author    = $wp_query->get_queried_object();
			$classes[] = 'author';
			if ( isset( $author->user_nicename ) ) {
				$classes[] = 'author-' . sanitize_html_class( $author->user_nicename, $author->ID );
				$classes[] = 'author-' . $author->ID;
			}
		} elseif ( is_category() ) {
			$cat       = $wp_query->get_queried_object();
			$classes[] = 'category';
			if ( isset( $cat->term_id ) ) {
				$cat_class = sanitize_html_class( $cat->slug, $cat->term_id );
				if ( is_numeric( $cat_class ) || ! trim( $cat_class, '-' ) ) {
					$cat_class = $cat->term_id;
				}

				$classes[] = 'category-' . $cat_class;
				$classes[] = 'category-' . $cat->term_id;
			}
		} elseif ( is_tag() ) {
			$tag       = $wp_query->get_queried_object();
			$classes[] = 'tag';
			if ( isset( $tag->term_id ) ) {
				$tag_class = sanitize_html_class( $tag->slug, $tag->term_id );
				if ( is_numeric( $tag_class ) || ! trim( $tag_class, '-' ) ) {
					$tag_class = $tag->term_id;
				}

				$classes[] = 'tag-' . $tag_class;
				$classes[] = 'tag-' . $tag->term_id;
			}
		} elseif ( is_tax() ) {
			$term = $wp_query->get_queried_object();
			if ( isset( $term->term_id ) ) {
				$term_class = sanitize_html_class( $term->slug, $term->term_id );
				if ( is_numeric( $term_class ) || ! trim( $term_class, '-' ) ) {
					$term_class = $term->term_id;
				}

				$classes[] = 'tax-' . sanitize_html_class( $term->taxonomy );
				$classes[] = 'term-' . $term_class;
				$classes[] = 'term-' . $term->term_id;
			}
		}
	}

	if ( is_user_logged_in() ) {
		$classes[] = 'logged-in';
	}

	if ( is_admin_bar_showing() ) {
		$classes[] = 'admin-bar';
		$classes[] = 'no-customize-support';
	}

	if ( current_theme_supports( 'custom-background' )
		&& ( get_background_color() !== get_theme_support( 'custom-background', 'default-color' ) || get_background_image() ) ) {
		$classes[] = 'custom-background';
	}

	if ( has_custom_logo() ) {
		$classes[] = 'wp-custom-logo';
	}

	if ( current_theme_supports( 'responsive-embeds' ) ) {
		$classes[] = 'wp-embed-responsive';
	}

	$page = $wp_query->get( 'page' );

	if ( ! $page || $page < 2 ) {
		$page = $wp_query->get( 'paged' );
	}

	if ( $page && $page > 1 && ! is_404() ) {
		$classes[] = 'paged-' . $page;

		if ( is_single() ) {
			$classes[] = 'single-paged-' . $page;
		} elseif ( is_page() ) {
			$classes[] = 'page-paged-' . $page;
		} elseif ( is_category() ) {
			$classes[] = 'category-paged-' . $page;
		} elseif ( is_tag() ) {
			$classes[] = 'tag-paged-' . $page;
		} elseif ( is_date() ) {
			$classes[] = 'date-paged-' . $page;
		} elseif ( is_author() ) {
			$classes[] = 'author-paged-' . $page;
		} elseif ( is_search() ) {
			$classes[] = 'search-paged-' . $page;
		} elseif ( is_post_type_archive() ) {
			$classes[] = 'post-type-paged-' . $page;
		}
	}

	if ( ! empty( $css_class ) ) {
		if ( ! is_array( $css_class ) ) {
			$css_class = preg_split( '#\s+#', $css_class );
		}
		$classes = array_merge( $classes, $css_class );
	} else {
		// Ensure that we always coerce class to being an array.
		$css_class = array();
	}

	$classes = array_map( 'esc_attr', $classes );

	$classes = apply_filters( 'body_class', $classes, $css_class );

	return array_unique( $classes );
}

通过阅读源码，可以看出 get_body_class 的工作原理，就是判断当前页面，然后不同页面增加不同的 class。利用这些 class ，就可以使页面 UI 更加个性化。

包含钩子：

apply_filters( 'body_class', string[] $classes, string[] $css_class )

利用 body_class 钩子，开发者还可以增加定制自己的 class。

使用举例：

最容易想到的使用方式，就是：

echo 'class="' . esc_attr( implode( ' ', get_body_class( $css_class ) ) ) . '"';

不过，还有一种有意思的用法，因为不同页面具有不同的 class ，所以可以根据 class 的不同判断页面。如下：

// If has "home" class in the body
if (in_array('home', get_body_class())) {
    // Class is present
} else {
    // Class is not present
}

貌似有点毛病，看看上面 get_body_class 函数的源码，直接使用 is_front_page 判断页面不行吗？