描述：

用于检查是否小工具/侧边栏已经在前端显示，若要生效，此函数必须在小工具初始化之后运行，

用法：

<?php is_active_widget( $callback, $widget_id, $id_base, $skip_inactive ); ?>

参数：

$callback

(string) (可选) 要检查的小工具回调。 默认值: False

$widget_id

(int) (可选) 要检查的小工具的ID。默认值: None

$id_base

(string) (可选) 通过WP_Widget创建的小工具的ID。默认值: None

$skip_inactive

(boolean) (可选) 是否签入“wp_inactive_widgets”。默认值: True

返回值

(mixed) 

如果指定的小工具未处于激活状态，或小工具处于激活状态的侧边栏的ID，则返回False。如果回调不是唯一的，您可以选择指定小工具的id。

源文件

is_active_widget() 函数的代码位于 wp-includes/widgets.php.

 /**
 * Whether widget is displayed on the front-end.
 *
 * Either $callback or $id_base can be used
 * $id_base is the first argument when extending WP_Widget class
 * Without the optional $widget_id parameter, returns the ID of the first sidebar
 * in which the first instance of the widget with the given callback or $id_base is found.
 * With the $widget_id parameter, returns the ID of the sidebar where
 * the widget with that callback/$id_base AND that ID is found.
 *
 * NOTE: $widget_id and $id_base are the same for single widgets. To be effective
 * this function has to run after widgets have initialized, at action 'init' or later.
 *
 * @since 2.2.0
 *
 * @global array $wp_registered_widgets
 *
 * @param string $callback      Optional, Widget callback to check.
 * @param int    $widget_id     Optional, but needed for checking. Widget ID.
 * @param string $id_base       Optional, the base ID of a widget created by extending WP_Widget.
 * @param bool   $skip_inactive Optional, whether to check in 'wp_inactive_widgets'.
 * @return string|false False if widget is not active or id of sidebar in which the widget is active.
 */
function is_active_widget($callback = false, $widget_id = false, $id_base = false, $skip_inactive = true) {
 global $wp_registered_widgets;

 $sidebars_widgets = wp_get_sidebars_widgets();

 if ( is_array($sidebars_widgets) ) {
 foreach ( $sidebars_widgets as $sidebar => $widgets ) {
 if ( $skip_inactive && ( 'wp_inactive_widgets' === $sidebar || 'orphaned_widgets' === substr( $sidebar, 0, 16 ) ) ) {
 continue;
 }

 if ( is_array($widgets) ) {
 foreach ( $widgets as $widget ) {
 if ( ( $callback && isset($wp_registered_widgets[$widget]['callback']) && $wp_registered_widgets[$widget]['callback'] == $callback ) || ( $id_base && _get_widget_id_base($widget) == $id_base ) ) {
 if ( !$widget_id || $widget_id == $wp_registered_widgets[$widget]['id'] )
 return $sidebar;
 }
 }
 }
 }
 }
 return false;
}