Get the name of category in query

Question

I have parent category, Game (cat ID 42), and some child categories in it: Acrade, Causaul. After I using the loop to get the title of the post, I want to have a child category name. But my code is not working:

<?php 
$args = array(
    'cat'            => 42,
    'posts_per_page' => 12,
    'post__in'       => get_option( 'sticky_posts' ),
);

// The Query
$the_query = new WP_Query( $args );
$categories = get_the_category($post->ID);

// The Loop
while ( $the_query->have_posts() ) : 
    $the_query->the_post();
?>

<?php
/* if post has a thumbnail */
if (  ( function_exists('has_post_thumbnail') ) && ( has_post_thumbnail() )  ) { ?>

<li>
  <a href="<?php the_permalink(); ?>" rel="bookmark" title="Permanent Link: <?php the_title(); ?>"><?php the_post_thumbnail('app_icon', array('title' => get_the_title())); ?></a>
  <p class="ptit">
    <a href="<?php echo get_permalink() ?>" rel="bookmark" title="Permanent Link: <?php the_title(); ?>"><?php the_title(); ?></a>
  </p>
  <span class="cate"><?php echo $categories ?></span>
</li>

<?php
} /* end if post has a thumbnail */

endwhile;

// Reset Post Data
wp_reset_postdata();
?>

Answer 1

When you call

$categories = get_the_category($post->ID);

the $post variable is not defined yet (or is not the one that you expect), because you have to use it inside the loop.

Where you have

<span class="cate"><?php echo $categories ?></span>

replace with (this will output something like "Game, Arcade")

<span class="cate"><?php the_category(', '); ?></span>

or if you want remove parent cat

<span class="cate">
<?php
$categories = get_the_category();
if( $categories ){
  $o = '';
  $sep = ', ';
  foreach($categories as $c) {
    if ( $c->parent == 0 ) continue;
    $o .= $c->cat_name . $sep;
  }
  echo rtrim($o, $sep);
}
?>
</span>

Answer 2

In the mainpage has working. But in navsidebar, the code is not work. My code in header.php. And i want to ask, how to only get thumbnail the first item, same the 1mobile page

<div class="mb10">
         <div class="sidetoplist">
             <div class="title"><h3 class="tit">Latest Games</h3></div>
             <div class="first"><a href="/subway-surfers-574540.html" class="pic"><img src="http://img.1mobile.com/market/iconv2/36/36542a7ff008ac4ab8440c34b8f02f40-s144.png" alt="Subway Surfers"></a></div>
             <ul class="list clearfix" id="topgames">
                                    <?php  

$args = array( 'cat' => 42, 'posts_per_page' => 10, 'orderby' => 'date' ); // The Query $count = 1; $the_query = new WP_Query( $args );

// The Loop while ( $the_query->have_posts() ) : $the_query->the_post(); ?>

                        <li><em class="num"><?php echo $count?>.</em><a href="<?php echo get_permalink() ?>" rel="bookmark" title="Permanent Link: <?php the_title(); ?>"><b><?php the_title(); ?></b><i><?php

$categories = get_the_category(); if( $categories ){ $o = ''; $sep = ', '; foreach($categories as $c) { if ( $c->parent == 0 ) continue; $o .= $c->cat_name . $sep; } echo rtrim($o, $sep); } ?>

                        <?php }
                        $count++;
                    endwhile;

// Reset Post Data wp_reset_postdata(); ?>

             </ul>
         </div>