WordPress 分类档案页面显示该分类置顶文章

    class StickyInCategory {

    	/**

    	 * A reference to an instance of this class.

    	 */

    	private static $instance;

    	/**

    	 * The array of categories that will have sticky posts moved to the top.

    	 */

    	protected $categories;

    	/**

    	 * Returns an instance of this class. 

    	 */

    	public static function get_instance() {

    		if ( null == self::$instance ) {

    			self::$instance = new StickyInCategory();

    		}

    		return self::$instance;

    	}

    	/**

    	 * Initializes the plugin by setting filters and administration functions.

    	 */

    	private function __construct() {

    		$this->categories = array();

    		// Filter retrieved posts

    		add_filter(	'the_posts', array( $this, 'prepend_sticky_posts' ), 10, 2 );

    		// Set the 'sticky' class

    		add_filter( 'post_class', array( $this, 'set_sticky_post_class' ), 10, 3 );

    	}

    	/**

    	 * Move sticky posts to the top of the archive listing.

    	 */

    	public function prepend_sticky_posts( $posts, $query ) {

    		if ( !is_admin() && is_main_query() ) {

    			// Hook to initialise the categories if none specified.

    			if ( empty( $this->categories ) ) {

    				$this->categories = apply_filters( 'sia_sticky_categories', $this->categories );

    			}

    			// Only continue if we are viewing a category archive.

    			if ( array_key_exists( 'category_name', $query->query_vars ) ) {

    				$category_matched = false;

    				if ( empty( $this->categories ) ) {

    					// If no categories were supplied by the apply_filters() then operate on all categories.

    					$category_matched = true;

    				}

    				else {

    					// Check whether the current category is in the list.

    					$category_matched = in_array( $query->query_vars['category_name'], $this->categories );

    				}

    				if ( $category_matched ) {

    					// Copied from the bottom of WP_Query::get_posts() in wp-includes/class-wp-query.php

    					$sticky_posts = get_option( 'sticky_posts' );

    					$num_posts = count( $posts );

    					$sticky_offset = 0;

    					// Loop over posts and relocate stickies to the front.

    					for ( $i = 0; $i < $num_posts; $i++ ) {

    						if ( in_array( $posts[ $i ]->ID, $sticky_posts ) ) {

    							$sticky_post = $posts[ $i ];

    							// Remove sticky from current position

    							array_splice( $posts, $i, 1 );

    							// Move to front, after other stickies

    							array_splice( $posts, $sticky_offset, 0, array( $sticky_post ) );

    							// Increment the sticky offset. The next sticky will be placed at this offset.

    							$sticky_offset++;

    							// Remove post from sticky posts array

    							$offset = array_search( $sticky_post->ID, $sticky_posts );

    							unset( $sticky_posts[ $offset ] );

    						}

    					}

    				}

    			}

    		}

    		return $posts;

    	}

    	/**

    	 * Set the 'sticky' post class. get_post_class() only does it on the home page.

    	 */

    	public function set_sticky_post_class( $classes, $class, $post_ID ) {

    		// TODO: Consider whether to reference $this->categories.

    		if ( is_archive() && is_sticky( $post_ID ) ) {

    			$classes[] = 'sticky';

    		}

    		return $classes;

    	}

    }

    add_action( 'after_setup_theme', array( 'StickyInCategory', 'get_instance' ) );