Gamajo Template Loader

A class to copy into your WordPress plugin, to allow loading template parts with fallback through the child theme > parent theme > plugin.

Description

Easy Digital Downloads, WooCommerce, and Events Calendar plugins, amongst others, allow you to add files to your theme to override the default templates that come with the plugin. As a developer, adding this convenience in to your own plugin can be a little tricky.

The get_template_part() function in WordPress was never really designed with plugins in mind, since it relies on locate_template() which only checks child and parent themes. So we can add in a final fallback that uses the templates in the plugin, we have to use a custom locate_template() function, and a custom get_template_part() function. The solution here just wraps them up as a class for convenience.

Installation

This isn't a WordPress plugin on its own, so the usual instructions don't apply. Instead:

Manually install class

Copy class-gamajo-template-loader.php into your plugin. It can be into a file in the plugin root, or better, an includes directory.

or:

Install class via Composer

Tell Composer to install this class as a dependency: composer require gamajo/template-loader
Recommended: Install the Mozart package: composer require coenjacobs/mozart --dev and configure it.
The class is now renamed to use your own prefix, to prevent collisions with other plugins bundling this class.

Implement class

Create a new file, such as class-your-plugin-template-loader.php, in the same directory.
Create a class in that file that extends Gamajo_Template_Loader (or the new prefixed name, if you installed via Composer/Mozart). You can see the Meal Planner Template Loader example class below as a starting point if it helps.
Override the class properties to suit your plugin. You could also override the get_templates_dir() method if it isn't right for you.
You can now instantiate your custom template loader class, and use it to call the get_template_part() method. This could be within a shortcode callback, or something you want theme developers to include in their files.

// Template loader instantiated elsewhere, such as the main plugin file.
$meal_planner_template_loader = new Meal_Planner_Template_Loader;

Use it to call the get_template_part() method. This could be within a shortcode callback, or something you want theme developers to include in their files.
```
$meal_planner_template_loader->get_template_part( 'recipe' );
```
If you want to pass data to the template, call the set_template_data() method with an array before calling get_template_part(). set_template_data() returns the loader object to allow for method chaining.
```
$data = array( 'foo' => 'bar', 'baz' => 'boom' );
$meal_planner_template_loader
    ->set_template_data( $data );
    ->get_template_part( 'recipe' );
```
The value of bar is now available inside the recipe template as $data->foo.

If you wish to use a different variable name, add a second parameter to set_template_data():
```
$data = array( 'foo' => 'bar', 'baz' => 'boom' );
$meal_planner_template_loader
    ->set_template_data( $data, 'context' )
    ->get_template_part( 'recipe', 'ingredients' );
```
The value of bar is now available inside the recipe template as $context->foo.

This will try to load up wp-content/themes/my-theme/meal-planner/recipe-ingredients.php, or wp-content/themes/my-theme/meal-planner/recipe.php, then fallback to wp-content/plugins/meal-planner/templates/recipe-ingredients.php or wp-content/plugins/meal-planner/templates/recipe.php.

Meal Planner Example Class

<?php
/**
 * Meal Planner
 *
 * @package   Meal_Planner
 * @author    Gary Jones
 * @link      http://example.com/meal-planner
 * @copyright 2013 Gary Jones
 * @license   GPL-2.0+
 */

if ( ! class_exists( 'Gamajo_Template_Loader' ) ) {
  require plugin_dir_path( __FILE__ ) . 'class-gamajo-template-loader.php';
}

/**
 * Template loader for Meal Planner.
 *
 * Only need to specify class properties here.
 *
 * @package Meal_Planner
 * @author  Gary Jones
 */
class Meal_Planner_Template_Loader extends Gamajo_Template_Loader {
  /**
   * Prefix for filter names.
   *
   * @since 1.0.0
   *
   * @var string
   */
  protected $filter_prefix = 'meal_planner';

  /**
   * Directory name where custom templates for this plugin should be found in the theme.
   *
   * @since 1.0.0
   *
   * @var string
   */
  protected $theme_template_directory = 'meal-planner';

  /**
   * Reference to the root directory path of this plugin.
   *
   * Can either be a defined constant, or a relative reference from where the subclass lives.
   *
   * In this case, `MEAL_PLANNER_PLUGIN_DIR` would be defined in the root plugin file as:
   *
   * ~~~
   * define( 'MEAL_PLANNER_PLUGIN_DIR', plugin_dir_path( __FILE__ ) );
   * ~~~
   *
   * @since 1.0.0
   *
   * @var string
   */
  protected $plugin_directory = MEAL_PLANNER_PLUGIN_DIR;

  /**
   * Directory name where templates are found in this plugin.
   *
   * Can either be a defined constant, or a relative reference from where the subclass lives.
   *
   * e.g. 'templates' or 'includes/templates', etc.
   *
   * @since 1.1.0
   *
   * @var string
   */
  protected $plugin_template_directory = 'templates';
}

Usage Example

The Cue plugin from AudioTheme uses this class. Starting at https://github.com/AudioTheme/cue/tree/develop/includes, it has this class in the vendor directory, then the required subclass of my class in the class-cue-template-loader.php file, which sets a few basic properties. It also has a template in https://github.com/AudioTheme/cue/tree/develop/templates.

If you wanted the playlist to have different markup for your theme, you'd copy templates/playlist.php to wp-content/themes/{your-active-theme}/cue/playlist.php and do whatever changes you wanted. WordPress will look for that file first, before then checking a parent theme location (if your active theme is a child theme), before falling back to the default template that comes with the Cue plugin.