How To: First and Last CSS Classes for Sidebar Widgets

Thought this might be useful to somebody–it’s a filter function that automatically adds “first and last” css classes to dynamic sidebar widgets. It also numbers each widget (“widget-1”, “widget-2”, etc.).

It’s a slight improvement on Greenshady’s code in this post (it keeps a separate counter for each sidebar, and knows the total number of widgets in the current sidebar).

Suggestions for improvement are welcome. It could easily be modified to add even/odd classes.

/**
 * Add "first" and "last" CSS classes to dynamic sidebar widgets. Also adds numeric index class for each widget (widget-1, widget-2, etc.)
 */
function widget_first_last_classes($params) {

	global $my_widget_num; // Global a counter array
	$this_id = $params[0]['id']; // Get the id for the current sidebar we're processing
	$arr_registered_widgets = wp_get_sidebars_widgets(); // Get an array of ALL registered widgets	

	if(!$my_widget_num) {// If the counter array doesn't exist, create it
		$my_widget_num = array();
	}

	if(!isset($arr_registered_widgets[$this_id]) || !is_array($arr_registered_widgets[$this_id])) { // Check if the current sidebar has no widgets
		return $params; // No widgets in this sidebar... bail early.
	}

	if(isset($my_widget_num[$this_id])) { // See if the counter array has an entry for this sidebar
		$my_widget_num[$this_id] ++;
	} else { // If not, create it starting with 1
		$my_widget_num[$this_id] = 1;
	}

	$class = 'class="widget-' . $my_widget_num[$this_id] . ' '; // Add a widget number class for additional styling options

	if($my_widget_num[$this_id] == 1) { // If this is the first widget
		$class .= 'widget-first ';
	} elseif($my_widget_num[$this_id] == count($arr_registered_widgets[$this_id])) { // If this is the last widget
		$class .= 'widget-last ';
	}

	$params[0]['before_widget'] = str_replace('class="', $class, $params[0]['before_widget']); // Insert our new classes into "before widget"

	return $params;

}
add_filter('dynamic_sidebar_params','widget_first_last_classes');