Load WordPress page templates from a plugin

custom-template.php

// This is the page template file

page-templates.php

<?php

class PageTemplater {

/**
* A Unique Identifier
*/
protected $plugin_slug;

/**
* A reference to an instance of this class.
*/
private static $instance;

/**
* The array of templates that this plugin tracks.
*/
protected $templates;


/**
* Returns an instance of this class.
*/
public static function get_instance() {

if( null == self::$instance ) {
self::$instance = new PageTemplater();
}

return self::$instance;

}

/**
* Initializes the plugin by setting filters and administration functions.
*/
private function __construct() {

$this->templates = array();


// Add a filter to the attributes metabox to inject template into the cache.
add_filter(
'page_attributes_dropdown_pages_args',
array( $this, 'register_project_templates' )
);


// Add a filter to the save post to inject out template into the page cache
add_filter(
'wp_insert_post_data',
array( $this, 'register_project_templates' )
);


// Add a filter to the template include to determine if the page has our
// template assigned and return it's path
add_filter(
'template_include',
array( $this, 'view_project_template')
);


// Add your templates to this array.
$this->templates = array(
'custom-template.php'     => 'Custom template',
);

}


/**
* Adds our template to the pages cache in order to trick WordPress
* into thinking the template file exists where it doens't really exist.
*
*/

public function register_project_templates( $atts ) {

// Create the key used for the themes cache
$cache_key = 'page_templates-' . md5( get_theme_root() . '/' . get_stylesheet() );

// Retrieve the cache list.
// If it doesn't exist, or it's empty prepare an array
$templates = wp_get_theme()->get_page_templates();
if ( empty( $templates ) ) {
$templates = array();
}

// New cache, therefore remove the old one
wp_cache_delete( $cache_key , 'themes');

// Now add our template to the list of templates by merging our templates
// with the existing templates array from the cache.
$templates = array_merge( $templates, $this->templates );

// Add the modified cache to allow WordPress to pick it up for listing
// available templates
wp_cache_add( $cache_key, $templates, 'themes', 1800 );

return $atts;

}

/**
* Checks if the template is assigned to the page
*/
public function view_project_template( $template ) {

global $post;

if (!isset($this->templates[get_post_meta(
$post->ID, '_wp_page_template', true
)] ) ) {

return $template;

}

$file = plugin_dir_path(__FILE__). get_post_meta(
$post->ID, '_wp_page_template', true
);

// Just to be safe, we check if the file exist first
if( file_exists( $file ) ) {
return $file;
}
else { echo $file; }

return $template;

}


}

add_action( 'plugins_loaded', array( 'PageTemplater', 'get_instance' ) );

plugin.php

<?php
/*
Plugin Name: PLugin name
Version: 0.0.1
Author: Keith Devon
Author URI: http://keithdevon.com/
*/

include "page-templates.php";

Hey,

I treid to use your plugin, but I dont see "custom-template.php" in page attributes dropdown.
Can you please help with this?

Thanks, Mosh