Insert to wp_footer if widget is found in the sidebar

Question

I trying to insert a code into wp_footer whether the widget is present or not in the sidebar.

How to avoid the unnecessary code in the footer?

Add the code only if widget is present the sidebar.

 class CustomWidget extends WP_Widget {

   function CustomWidget() { 
     add_action( 'wp_footer', array($this,'footer'), 10, 1 );   
   }

   function widget($args, $instance) { }

   function update( $new_instance, $old_instance ) {}

   function form($instance) {}

   function footer {
      $all_widgets = $this->get_settings();

      foreach ($all_widgets as $key => $wpdcjqverticalmegamenu){

       $widget_id = $this->id_base . '-' . $key;

      if(is_active_widget(false, $widget_id, $this->id_base)){

      }     

   }

}

Answer 1

The constructor of widget is called when the widget is registered, so your add_action is called on (probably) every request. You can avoid that simply put the add_action inside widget() function, that is called only when the widget is printed so there is no need to check: just output what you want.

Also, if you need some context inside the footer method you can use a closure inside the widget method where you have easy access to $args and $instance variables (the first contain information about the sidebar and the widget id, the second contain informations on the fields setted for speficic widget):

class CustomWidget extends WP_Widget {

   function __construct() { 
      parent::__construct( 'my-widget-id', 'My Widget Name' );
   }

   function widget( $args, $instance ) {

    add_action( 'wp_footer', function() use ( $args, $instance ) {

      echo '<h1>' . $args['widget_id'] . '</h1>';
      echo '<pre>'; print_r( $instance ); echo '</pre>';
      echo '<pre>'; print_r( $args); echo '</pre>';
      echo '<hr>';

    }); 

   }

   function update( $new_instance, $old_instance ) {}

   function form($instance) {}

}

that makes the closure all the times the widget is added to page, i.e. if the widget is added 3 times, the closure will run 3 times.

If you want to prevent that use a static flag:

class CustomWidget extends WP_Widget {

   static $added = 0;

   function __construct() { 
      parent::__construct( 'my-widget-id', 'My Widget Name' );
   }

   function widget( $args, $instance ) {

    add_action( 'wp_footer', function() use ( $args, $instance ) {

      if ( static::$added !== 0 ) return; // run only once;
      static::$added++;

      echo '<h1>' . $args['widget_id'] . '</h1>';
      echo '<pre>'; print_r( $instance ); echo '</pre>';
      echo '<pre>'; print_r( $args); echo '</pre>';
      echo '<hr>';

    }); 

   }

   function update( $new_instance, $old_instance ) {}

   function form($instance) {}

}

^{PS: PHP 4 died a long time ago. Please use PHP 5 constructors...}