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

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.

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

1. Copy class-gamajo-template-loader.php into your plugin. It can be into a file in the plugin root, or better, an includes directory.
2. Create a new file, such as class-your-plugin-template-loader.php, in the same directory.
3. Create a class in that file that extends Gamajo_Tech_Loader. You can copy the meal planner example class as a starting point if it helps.
4. Override the class properties to suit your plugin. You could also override the get_templates_dir() method if it isn't right for you.
5. 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.
6. Optionally, you can wrap the reference to the object in a functions e.g.

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

// ...

// This function can live wherever is suitable in your plugin
function meal_planner_get_template_part( $slug, $name = null, $load = true ) {
    global $meal_planner_template_loader;
    $meal_planner_template_loader->get_template_part( $slug, $name, $load );
}

7. An example using the helper function (or class method) would be:

add_filter( 'the_content', 'meal_planner_single_recipe_content' );
function meal_planner_single_recipe_content( $content ) {
    if ( ! function_exists( 'meal_planner_get_template_part' ) ) {
        return $content;
    }
    meal_planner_get_template_part( 'recipe', 'ingredients' );
    meal_planner_get_template_part( 'recipe', 'instructions' );
}

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/themes/plugins/meal-planner/templates/recipe-ingredients.php or wp-content/themes/plugins/meal-planner/templates/recipe.php.

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.

Contributions are welcome - fork, fix and send pull requests against the develop branch please.

Built by Gary Jones
Copyright 2013 Gamajo Tech