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);
}