Code for a tutorial on adding columns to WordPress list tables.

list-table-tut.php

<?php
/*
Plugin Name: List Table Tutorial
Plugin URI: http://pmg.co/wp-list-table-tutorial
Description: How to add a column to WordPress list tables.
Version: 1.0
Text Domain: pmg-list-table
Author: Christopher Davis
Author URI: http://christopherdavis.me
License: GPL2

    Copyright 2012 Christopher Davis

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License, version 2, as 
    published by the Free Software Foundation.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/

add_action('load-edit.php', 'pmg_ltt_load');
/**
 * Fires whenever the `edit.php` page loads in the admin area. First checks to
 * see that we're on the pages list table, then adds the filters we need to
 * modify the list table.
 *
 * @uses    get_current_screen
 * @uses    add_filter
 * @uses    add_action
 */
function pmg_ltt_load()
{
    $screen = get_current_screen();

    if(!isset($screen->post_type) || 'page' != $screen->post_type)
        return;

    add_filter(
        "manage_{$screen->id}_columns",
        'pmg_ltt_add_columns'
    );

    add_filter(
        "manage_{$screen->id}_sortable_columns",
        'pmg_ltt_add_sortable'
    );

    add_action(
        "manage_{$screen->post_type}_posts_custom_column",
        'pmg_ltt_column_cb',
        10,
        2
    );

    add_filter(
        'request',
        'pmg_ltt_do_sort'
    );
}


/**
 * Hooked into `manage{$screen->id}_columns` on the page list table.  Adds a 
 * new column for the page template.
 *
 * @param   array $cols The array of columns in $key => $label pairs
 * @return  array
 */
function pmg_ltt_add_columns($cols)
{
    $cols['template'] = __('Page Template', 'pmg-list-table');
    return $cols;
}


/**
 * Hooked into `manage_{$screen->id}_sortable_columns`.  Enables the template
 * column for sorting.
 *
 * @param   array $cols The sortable columns. $key => $url_param_value pairs
 * @return  array
 */
function pmg_ltt_add_sortable($cols)
{
    $cols['template'] = 'template';
    return $cols;
}


/**
 * Column callback.  Checks to make sure we're on the `template` column, then
 * fetchs the post template, printing out its name.
 *
 * @param   string $col The column key
 * @param   int $post_id The post id for the row
 * @uses    get_post_meta
 * @uses    get_page_templates
 * @uses    esc_html_e
 * @return  null
 */
function pmg_ltt_column_cb($col, $post_id)
{
    static $templates;

    if('template' == $col)
    {
        // wtf would you do $label => $filename from get_page_templates?
        if(empty($templates))
            $templates = array_flip(get_page_templates());

        $tmp = get_post_meta($post_id, '_wp_page_template', true);
        if($tmp && isset($templates[$tmp]))
        {
            echo esc_html($templates[$tmp]);
        }
        else
        {
            esc_html_e('Default Template', 'pmg-list-table');
        }
    }
}


/**
 * Hooked into `request` modifies the query to include custom sorting if needed
 *
 * @param   array $vars The query variable
 * @param   array
 */
function pmg_ltt_do_sort($vars)
{
    if(isset($vars['orderby']) && 'template' == $vars['orderby'])
    {
        // WordPress is trying to order by template. Let's modify the query to
        // order by the appropriate meta key.
        $vars['meta_key'] = '_wp_page_template';
        $vars['orderby'] = 'meta_value';
    }
    return $vars;
}