根據需求模仿著wordpress官方原生小工具（widget） 寫了一個能夠列出指定分類目錄下最新文章列表的小工具。代碼如下（先貼出來，以後有空再做解釋說明）：
1<?php
2 function register_catlist_widget(){
3 register_widget('catlist_widget');
4 }
5 add_action('widgets_init','register_catlist_widget');
6
7 class Catlist_Widget extends WP_Widget{
8 /**
9 * 定义WP_Widget扩展类，设置小工具名和描述
10 * Sets up the widget name and description
11 */
12 public function __construct(){
13 $widget_ops = array('classname' => 'catlist_widget', 'description' => '指定分類目錄與顯示數目' );
14 // parent::__construct(）调用父类定义函数
15 parent::__construct(
16 'category-post-list', // Base ID
17 __('指定分類目錄文章列表','text_domain'), // Name
18 $widget_ops // Args
19 );
20
21 // add_action( $tag, $function_to_add);
22 add_action( 'save_post', array($this, 'flush_widget_cache') );
23 add_action( 'deleted_post', array($this, 'flush_widget_cache') );
24 add_action( 'switch_theme', array($this, 'flush_widget_cache') );
25
26 }
27
28 /**
29 * Outputs the content of the widget
30 * @param [array] $args [description]
31 * @param [array] $instance [description]
32 * @return [type] [description]
33 */
34 public function widget($args,$instance){
35 $cache = array();
36 if ( ! $this->is_preview() ) {
37 $cache = wp_cache_get( 'catlist_posts', 'widget' );
38 }
39
40 if ( ! is_array( $cache ) ) {
41 $cache = array();
42 }
43
44 if ( ! isset( $args['widget_id'] ) ) {
45 $args['widget_id'] = $this->id;
46 }
47
48 if ( isset( $cache[ $args['widget_id'] ] ) ) {
49 echo $cache[ $args['widget_id'] ];
50 return;
51 }
52
53 ob_start();
54
55
56 $title = ( ! empty( $instance['title'] ) ) ? $instance['title'] : '分類文章列表';
57 $title = apply_filters( 'widget_title', $title, $instance, $this->id_base );
58
59 $number = ( ! empty( $instance['num'] ) ) ? absint( $instance['num'] ) : 10;
60 if ( ! $number )
61 $number = 10;
62 $catid = ( ! empty( $instance['cat'] ) ) ? absint( $instance['cat'] ) : 1;
63 if ( ! $catid )
64 $catid = 1;
65
66 global $post;
67 $r = new WP_Query( apply_filters('widget_posts_args', array(
68 'posts_per_page' => $number,
69 'cat' => $catid,
70 'post_status' => 'publish',
71 'no_found_rows' => true
72 )));
73 if ($r->have_posts()) :
74 ?>
75 <?php echo $args['before_widget']; ?>
76 <?php if ( $title ) {
77 echo $args['before_title'] . $title . $args['after_title'];
78 } ?>
79 <ul>
80 <?php while ( $r->have_posts() ) : $r->the_post(); ?>
81 <li>
82 <a href="<?php the_permalink(); ?>"><?php get_the_title() ? the_title() : the_ID(); ?></a>
83 </li>
84 <?php endwhile; ?>
85 <li><a href="<?php echo get_category_link($catid); ?>">more...</a></li>
86 </ul>
87 <?php echo $args['after_widget']; ?>
88 <?php
89 // Reset the global $the_post as this query will have stomped on it
90 wp_reset_postdata();
91
92 endif;
93
94 if ( ! $this->is_preview() ) {
95 $cache[ $args['widget_id'] ] = ob_get_flush();
96 wp_cache_set( 'catlist_posts', $cache, 'widget' );
97 } else {
98 ob_end_flush();
99 }
100 }
101 public function update( $new_instance, $old_instance ) {
102 $instance = $old_instance;
103 $instance['title'] = strip_tags($new_instance['title']);
104 $instance['num'] = (int) $new_instance['number'];
105 $instance['cat'] = (int) $new_instance['cat'];
106 $this->flush_widget_cache();
107
108 $alloptions = wp_cache_get( 'alloptions', 'options' );
109 if ( isset($alloptions['catlist_widget']) )
110 delete_option('catlist_widget');
111
112 return $instance;
113 }
114
115 public function flush_widget_cache() {
116 wp_cache_delete('catlist_posts', 'widget');
117 }
118
119
120 /**
121 * Back-end widget form.
122 * @see WP_Widget::form()
123 * @param [array] $instance [description]
124 * @return [type] [description]
125 */
126 public function form($instance){
127 $title = isset( $instance['title'] ) ? esc_attr( $instance['title'] ) : '';
128 $number = isset( $instance['num'] ) ? absint( $instance['num'] ) : 10;
129 $catid = isset( $instance['cat']) ? absint( $instance['cat'] ):'';
130 ?>
131 <p><label for="<?php echo $this->get_field_id( 'title' ); ?>"><?php _e( 'Title:' ); ?></label>
132 <input class="widefat" id="<?php echo $this->get_field_id( 'title' ); ?>" name="<?php echo $this->get_field_name( 'title' ); ?>" type="text" value="<?php echo $title; ?>" /></p>
133
134 <p><label for="<?php echo $this->get_field_id( 'number' ); ?>"><?php _e( 'Number of posts to show:' ); ?></label>
135 <input id="<?php echo $this->get_field_id( 'number' ); ?>" name="<?php echo $this->get_field_name( 'number' ); ?>" type="text" value="<?php echo $number; ?>" size="3" /></p>
136
137 <p><label><?php wp_dropdown_categories(array('name'=>$this->get_field_name('cat'),'selected'=>$instance['cat']));?></label></p>
138 <?php
139 }
140 }
在小工具（widget）界面添加後的設置效果如下圖示：
参考官方文档：Widgets API。