Add Taxonomy filter to Custom Post Type

Almost every time I use Custom post types i find myself using a custom taxonomy or two and  lately i found the need of filtering the custom post type posts on the admin edit list by these custom taxonomy and since I don't like to write the same code over and over here is a simple class that gets the job done.

Screenshot

The code

<?php
if (!class_exists('Tax_CTP_Filter')){
  /**
	* Tax CTP Filter Class 
	* Simple class to add custom taxonomy dropdown to a custom post type admin edit list
	* @author Ohad Raz <admin@bainternet.info>
	* @version 0.1
	*/
	class Tax_CTP_Filter
	{
		/**
		 * __construct 
		 * @author Ohad Raz <admin@bainternet.info>
		 * @since 0.1
		 * @param array $cpt [description]
		 */
		function __construct($cpt = array()){
			$this->cpt = $cpt;
			// Adding a Taxonomy Filter to Admin List for a Custom Post Type
			add_action( 'restrict_manage_posts', array($this,'my_restrict_manage_posts' ));
		}
 
		/**
		 * my_restrict_manage_posts  add the slelect dropdown per taxonomy
		 * @author Ohad Raz <admin@bainternet.info>
		 * @since 0.1
		 * @return void
		 */
		public function my_restrict_manage_posts() {
		    // only display these taxonomy filters on desired custom post_type listings
		    global $typenow;
		    $types = array_keys($this->cpt);
		    if (in_array($typenow, $types)) {
		        // create an array of taxonomy slugs you want to filter by - if you want to retrieve all taxonomies, could use get_taxonomies() to build the list
		        $filters = $this->cpt[$typenow];
		        foreach ($filters as $tax_slug) {
		            // retrieve the taxonomy object
		            $tax_obj = get_taxonomy($tax_slug);
		            $tax_name = $tax_obj->labels->name;
 
		            // output html for taxonomy dropdown filter
		            echo "<select name='".strtolower($tax_slug)."' id='".strtolower($tax_slug)."' class='postform'>";
		            echo "<option value=''>Show All $tax_name</option>";
		            $this->generate_taxonomy_options($tax_slug,0,0,(isset($_GET[strtolower($tax_slug)])? $_GET[strtolower($tax_slug)] : null));
		            echo "</select>";
		        }
		    }
		}
		
		/**
		 * generate_taxonomy_options generate dropdown
		 * @author Ohad Raz <admin@bainternet.info>
		 * @since 0.1
		 * @param  string  $tax_slug 
		 * @param  string  $parent   
		 * @param  integer $level    
		 * @param  string  $selected 
		 * @return void            
		 */
		public function generate_taxonomy_options($tax_slug, $parent = '', $level = 0,$selected = null) {
		    $args = array('show_empty' => 1);
		    if(!is_null($parent)) {
		        $args = array('parent' => $parent);
		    }
		    $terms = get_terms($tax_slug,$args);
		    $tab='';
		    for($i=0;$i<$level;$i++){
		        $tab.='--';
		    }
 
		    foreach ($terms as $term) {
		        // output each select option line, check against the last $_GET to show the current option selected
		        echo '<option value='. $term->slug, $selected == $term->slug ? ' selected="selected"' : '','>' .$tab. $term->name .' (' . $term->count .')</option>';
		        $this->generate_taxonomy_options($tax_slug, $term->term_id, $level+1,$selected);
		    }
 
		}
	}//end class
}//end if

Usage

Once you have the class in place it's easy to use as a single line of code:

new Tax_CTP_Filter(array('CUSTOM_POST_TYPE_NAME' => array('CUSTOM_TAXONOMY_NAME1','CUSTOM_TAXONOMY_NAME2')));

Now lets break it down: CUSTOM_POST_TYPE_NAME is the name of my custom post type, CUSTOM_TAXONOMY_NAME1 and CUSTOM_TAXONOMY_NAME2 are the name of my custom taxonomies.

So lets say for example i have a custom post type "Book" with a "genre" and "author" taxonomies all i have to do is:

new Tax_CTP_Filter(array('book' => array('genre','author')));

Also if you you can use one instance of the class to add taxonomy filters to multiple post type:

new Tax_CTP_Filter(array(
    'book' => array('genre','author'),
    'movie' => array('genre','actors'),
    'task' => array('task_status'),
));

If you get the idea, enjoy.