Error display post thumbnails for previous and next post

Question

I managed to display the thumbnails for the previous and next post on my custom post type but I keep getting this error

"Notice: Trying to get property of non-object in C:\xampp\htdocs\tba\wp-content\themes\artikulo-uno\single-news_press.php on line 137"

I tried researching it but found no luck for a fix on my problem. Here is the code I have been working on.

Show thumbnail of previous post

  <?php


  $prev_post = get_previous_post(true);

  $prev_thumbnail = get_the_post_thumbnail ( $prev_post->ID, array(100, 100) );

  previous_post_link( $prev_thumbnail . '%link', '<span class="prev-link"> <span>Previous Post</span> <br/> %title </span>'  );

  ?>

Show thumbnail of next post

      <?php

      $next_post = get_previous_post(true);

      $next_thumbnail = get_the_post_thumbnail ( $next_post->ID, array(100, 100) );

      next_post_link( $next_thumbnail . '%link', '<span class="next-link"><span>Next Post </span><br/> %title </span>' );
       ?>

Answer 1

That message is a general PHP error saying that you are trying to use a variable like a PHP object when it is not a PHP object. If you read the docs for get_previous_post() and get_next_post(), you can see that those functions return a post object or null/empty string if the previous/next post couldn't be determined. So, you need to check that you have an object before trying to use it:

$prev_post = get_previous_post(true);
if( is_object( $prev_post ) ) {
    $prev_thumbnail = get_the_post_thumbnail ( $prev_post->ID, array(100, 100) );
    previous_post_link( $prev_thumbnail . '%link', '<span class="prev-link"> <span>Previous Post</span> <br/> %title </span>'  );
}

$next_post = get_next_post(true);
if( is_object( $next_post ) ) {
    $next_thumbnail = get_the_post_thumbnail ( $next_post->ID, array(100, 100) );
    next_post_link( $next_thumbnail . '%link', '<span class="next-link"><span>Next Post </span><br/> %title </span>' );
}