List posts of assigned categories in list of all categories on single.php

Question

here's what I'm trying to accomplish:

I've got several categories, each of them have several posts. Now, on category.php I'm able to output a list of all categories and, inside this list, show a list of the posts of the current category.

• Cars (class: currentcat)
  • Hyunday
  • BMW
  • Mercedes
• Architects
• Popular First Names
• Football Teams

Actually I output the specific posts for each category but hide them via CSS and show only those of currentcat. When viewing a single post on single.php (eg "Mercedes"), I want the same, but for all categories assigned:

• Cars (class: currentcat)
  • Hyunday
  • BMW
  • Mercedes
• Architects
• Popular First Names (class: currentcat)
  • Steve
  • Matilda
  • Mercedes
• Football Teams

(Please pardon this excellent example.) On category.php I'm using:

 <ul>
      <?php
      $cargs = array(
        'type'                     => 'post',
        'child_of'                 => 0,
        'parent'                   => '',
        'orderby'                  => 'name',
        'order'                    => 'ASC',
        'hide_empty'               => 0,
        'hierarchical'             => 1,
        'exclude'                  => '1',
        'include'                  => '',
        'number'                   => '',
        'taxonomy'                 => 'category',
        'pad_counts'               => false 
      ); 
      $categories=get_categories($cargs);
      foreach($categories as $category) {
           if($cat != $category->term_id) {
                echo '<li class="zk_category-item"><a href="'.get_category_link($category->cat_ID).'">'.$category->cat_name."</a><ul>";
            }
            else {
                echo '<li class="currentcat"><a href="'.get_category_link($category->cat_ID).'" class="activelink">'.$category->cat_name."</a><ul>";
            }
           $category_posts=get_posts('category='.$category->cat_ID);
           foreach($category_posts as $post) {
                echo '<li class="zk_project-item"><a href="'.$post->guid.'">'.$post->post_title.'</a></li>';
            };
           echo "</ul></li>";
        };
        ?>
 </ul>

I see why this can't work on single.php, but I have no idea how to adjust it to make it work for single posts which might have several categories assigned.

I thought about and tried getting an array of all assigned categories of the current post on single.php and checking whether $category->term_id appears in this array, but to no avail.

Any help is highly appreciated!

Answer 1

Solved it with following code. My idea posted above worked out, but I had to rearrange the assigned categories in a new array.

<ul>
<?php
    $cargs = array(
        'type'                     => 'post',
        'child_of'                 => 0,
        'parent'                   => '',
        'orderby'                  => 'name',
        'order'                    => 'ASC',
        'hide_empty'               => 0,
        'hierarchical'             => 1,
        'exclude'                  => '1',
        'include'                  => '',
        'number'                   => '',
        'taxonomy'                 => 'category',
        'pad_counts'               => false 

    ); 
    $categories = get_categories($cargs);
    $post = $wp_query->post;
    $postid = $post->ID;
    $postcategories = get_the_terms($postid, 'category');
    $postcategoriesids = array();
    foreach ($postcategories as $postcategory) {
        $postcategoriesids[] = $postcategory->term_id;
    };
    foreach($categories as $category) {
        if(in_array($category->term_id, $postcategoriesids)) {
            echo '<li class="currentcat"><a href="'.get_category_link($category->cat_ID).'" class="activelink">'.$category->cat_name."</a><ul>";
        }
        else {
            echo '<li class="zk_category-item"><a href="'.get_category_link($category->cat_ID).'">'.$category->cat_name."</a><ul>";
        }
        $category_posts=get_posts('category='.$category->cat_ID);
        foreach($category_posts as $post) {
            echo '<li class="zk_project-item"><a href="'.$post->guid.'">'.$post->post_title.'</a></li>';
        };
        echo "</ul></li>";
    };
?>