浅析Wordpress的插件执行流程

1、首先，我现在pugins文件夹下写一个自己的插件
复制PHP内容到剪贴板
PHP代码:

<?php 
/*
Plugin Name: test
Plugin URI: [url=http://wordpress.org/]http://wordpress.org/[/url]#
Description: 我测试用的
Author: lw(fantasy)
Version: 0.1
Author URI: [url=http://www.xxx.com/]http://www.xxx.com/[/url] 
*/ 
 
$test = "<div id=my_test>这是我的第一个插件!</div>";

function output(){ 
    global $test;
    echo $test;
}

add_action(wp_footer,output);
?>

然后在后台启用。。

2、WP执行是加载在”wp-settings.php”，而在此文件中，可以找到以下与插件相关的代码片断：
复制PHP内容到剪贴板
PHP代码:
if ( get_option(active_plugins) ) {
$current_plugins = get_option(active_plugins);
dump($current_plugins);
if ( is_array($current_plugins) ) {
  foreach ($current_plugins as $plugin) {
   if ( != $plugin && 0 == validate_file($plugin) && file_exists(WP_PLUGIN_DIR . / . $plugin) )
    include_once(WP_PLUGIN_DIR . / . $plugin);
  }
}
}

我dump了一下$current_plugins，得到

Array
(
    [0] => Fanfou-Daily/Fanfou-Daily.php
    [1] => mulberrykit.php
    [2] => test.php
)

可以看到我写的test.php插件已经被include进去了。。

3、在主题模板里的footer.php里面会执行一个函数
<?php wp_footer(); ?>

而这个wp_footer里面又执行

do_action(wp_footer);

而这个do_action就是执行前面我们已经注册了的【add_action(wp_footer,output); 】output()函数。。。

这样就输出了"<div id=my_test>这是我的第一个插件!</div>"了

最后贴一下do_action的源码，大家体会一下吧
复制PHP内容到剪贴板
PHP代码:
/**
* do_action() - Execute functions hooked on a specific action hook.
*
* This function invokes all functions attached to action hook <tt>$tag</tt>.
* It is possible to create new action hooks by simply calling this function,
* specifying the name of the new hook using the <tt>$tag</tt> parameter.
*
* You can pass extra arguments to the hooks, much like you can with apply_filters().
*
* @see apply_filters() This function works similar with the exception that nothing is
* returned and only the functions or methods are called.
*
* @package WordPress
* @subpackage Plugin
* @since 1.2
* @global array $wp_filter Stores all of the filters
* @global array $wp_actions Increments the amount of times action was triggered.
*
* @param string $tag The name of the action to be executed.
* @param mixed $arg,... Optional additional arguments which are passed on to the functions hooked to the action.
* @return null Will return null if $tag does not exist in $wp_filter array
*/
function do_action($tag, $arg = ) {
global $wp_filter, $wp_actions, $merged_filters, $wp_current_filter;
if ( is_array($wp_actions) )
  $wp_actions[] = $tag;
else
  $wp_actions = array($tag);
$wp_current_filter[] = $tag;
// Do all actions first
if ( isset($wp_filter[all]) ) {
  $all_args = func_get_args();
  _wp_call_all_hook($all_args);
}
if ( !isset($wp_filter[$tag]) ) {
  array_pop($wp_current_filter);
  return;
}
$args = array();
if ( is_array($arg) && 1 == count($arg) && is_object($arg[0]) ) // array(&$this)
  $args[] =& $arg[0];
else
  $args[] = $arg;
for ( $a = 2; $a < func_num_args(); $a++ )
  $args[] = func_get_arg($a);
// Sort
if ( !isset( $merged_filters[ $tag ] ) ) {
  ksort($wp_filter[$tag]);
  $merged_filters[ $tag ] = true;
}
reset( $wp_filter[ $tag ] );
do {
  foreach ( (array) current($wp_filter[$tag]) as $the_ )
   if ( !is_null($the_[function]) )
    call_user_func_array($the_[function], array_slice($args, 0, (int) $the_[accepted_args]));
} while ( next($wp_filter[$tag]) !== false );
array_pop($wp_current_filter);
}

其中比较关键的就是call_user_func_array($the_[function], array_slice($args, 0, (int) $the_[accepted_args]));这句了