How to control output of custom post type without modifying theme?

Question

I have a custom post type 'properties' that I'd like to control the HTML output for. For simplicity, let's focus on the archive view.

As a basic example, here is what a loop looks like in an archive.php file:

<?php while ( have_posts() ) : the_post(); ?>
    <h2><?php the_title(); ?></h2>
    <div><?php the_content(); ?></div>
<?php endwhile; ?>

I'd like to be able to modify the output of the loop with my custom 'properties' HTML without adding a new template or using a shortcode - basically, without user intervention. Just to be clear, I'd like to replace the <h2> and <div> in the above example, and nothing before/after it.

Note: The above is only an example. I would like to control the loop output regardless of theme.

Right now I am using output buffering to capture the output from loop_start to loop_end and replacing it with my own, but this potentially can create conflicts with other plugins.

Is there an accepted/better way to do this?

Answer 1

There're two very often forgotten action ref arrays: loop_start/_end().

Just turn on output buffering and you're ready to go.

add_action( 'loop_start', 'wpse75307_plugin_loop' );
add_action( 'loop_end', 'wpse75307_plugin_loop' );
/**
 * Callback function triggered during:
 * + 'loop_start'/`have_posts()` after the last post gets rendered
 * + 'loop_end'/`the_post()` before the 1st post gets rendered
 * @param  object \WP_Query Passed by reference
 * @return 
 */
function wpse75307_plugin_loop( &$obj )
{
    # if ( is_main_query() )
    # DO STUFF ... OR DONT
    global $post;

    // Start output buffering at the beginning of the loop and abort
    if ( 'loop_start' === current_filter() )
        return ob_start();

    // At the end of the loop, we end the buffering and save into a var
    # if ( is_main_query() )
    # DO STUFF ... OR DONT
    $loop_content = ob_get_flush();

    // You can do something with $loop_content...
    // Add your own loop, or...
    // Whatever you can imagine
}

Note: I wouldn't do it like this, but as you said, you want exactly that level of overriding, here you go.

Answer 2

You can change the loop via hook, like this for cpt 'my_post_type '

// $this? - example was used in class-structures
// add custom post type to wp loop
add_filter( 'pre_get_posts', array( $this, 'add_to_query') );

// ads to query
function add_to_query( $query ) {

    if ( is_admin() || is_preview() )
        return;

    if ( ! isset( $query -> query_vars['suppress_filters'] ) )
        $query -> query_vars['suppress_filters'] = FALSE;

    // conditional tags for restrictions
    if ( is_home() || is_front_page() && ( FALSE == $query -> query_vars['suppress_filters'] ) ) 
        $query->set( 'post_type', array( 'post', 'my_post_type' ) );

    return $query;
}

Answer 3

If remembering well, I derived this technique from here: Use template_include with custom post types.

We use a plugin that will generate a "Virtual Template" for a given Post Type. The filter template_include will render a template file that resides in the plugin folder.

You have to refine the function custom_template and the template file to suit your needs. Hope this helps ;)

---

Plugin File

^{adjust the post_type name in the class instantiation}

<?php
! defined( 'ABSPATH' ) AND exit;
/*
Plugin Name: Virtual Template for CPT
Plugin URI: http://wordpress.stackexchange.com/q/75307/12615
Description: Use the plugin's template file to render an outsider loop.
Author: brasofilo
Author URI: http://wordpress.stackexchange.com/users/12615/brasofilo
Version: 2012.12.11
License: GPLv2
*/

$virtual_template = new VirtualTemplateForCPT_class( 'movies' );

class VirtualTemplateForCPT_class
{   
    private $pt;
    private $url;
    private $path;

    /**
     * Construct 
     *
     * @return void
     **/
    public function __construct( $pt )
    {       
        $this->pt = $pt;
        $this->url = plugins_url( '', __FILE__ );
        $this->path = plugin_dir_path( __FILE__ );
        add_action( 'init', array( $this, 'init_all' ) );
    }


    /**
     * Dispatch general hooks
     *
     * @return void
     **/
    public function init_all() 
    {
        add_action( 'wp_enqueue_scripts',   array( $this, 'frontend_enqueue' ) );
        add_filter( 'body_class',           array( $this, 'add_body_class' ) );
        add_filter( 'template_include',     array( $this, 'custom_template' ) );
    }

    /**
     * Use for custom frontend enqueues of scripts and styles
     * http://codex.wordpress.org/Plugin_API/Action_Reference/wp_enqueue_scripts
     *
     * @return void
     **/
    public function frontend_enqueue() 
    {
        global $post;
        if( $this->pt != get_post_type( $post->ID ) )
            return;         
    }

    /**
     * Add custom class to body tag
     * http://codex.wordpress.org/Function_Reference/body_class
     *
     * @param array $classes
     * @return array
     **/
    public function add_body_class( $classes ) 
    {
        global $post;
        if( $this->pt != get_post_type( $post->ID ) )
            return $classes;

        $classes[] = $this->pt . '-body-class';
        return $classes;
    }

    /**
     * Use the plugin template file to display the CPT
     * http://codex.wordpress.org/Conditional_Tags
     *
     * @param string $template
     * @return string
     **/
    public function custom_template( $template ) 
    {
        $post_types = array( $this->pt );
        $theme = wp_get_theme();

        if ( is_post_type_archive( $post_types ) )
            $template = $this->path . '/single-virtual-cpt.php';

        if ( is_singular( $post_types ) )
            $template = $this->path . '/single-virtual-cpt.php';

        return $template;
    }

}

---

Template file

single-virtual-cpt.php
^{put in the same folder as the plugin file}

<?php
/**
 * A custom -not from the theme- template
 *
 * @package WordPress
 * @subpackage Virtual_Template
 */

get_header(); 

while ( have_posts() ) : the_post(); $theID = $post->ID; 
    _e('This is a virtual template for the post:<br />');
    the_title();
endwhile; 
get_footer(); 

?>
</body>
</html>

---

Result

_{click to enlarge ⤴}