get_the_ID not returning correct ID value

Question

I have a loop (the_loop) to echo featured images on my slider but I need to filter it to specific post ID only. But get_the_ID is not working.

Here's my code

<?$valid_post_id('1','2','3','4');?>
<?php while( have_posts() ) : the_post(); ?>
       <?if(in_array(get_the_ID(),$valid_post_id)):?>
          <li class="slide">
             <div id="post-<?php the_ID(); ?>" <?php post_class(); ?><?php if( isset( $thumbnail ) ) : ?> style="background:url(<?php echo $thumbnail[0]; ?>) center no-repeat"<?php endif; ?>>
                    <div class="opacity"></div>
                    <a class="overlay" href="<?php the_permalink(); ?>" rel="bookmark"></a>
                    <div class="entry-container">
                        <h2 class="entry-title"><a href="<?php the_permalink(); ?>" title="<?php the_title_attribute(); ?>" rel="bookmark"><?php the_title(); ?></a></h2>
                        <div class="entry-summary">
                            <?php the_excerpt(); ?>
                            <div class="clear"></div>
                        </div><!-- .entry-summary -->
                    </div><!-- .entry-container -->
                </div><!-- .post -->
          </li>
       <?endif;?>
<?php endwhile; ?>

Answer 1

The array intialize of the variable $valid_post_id is incorrect.

Change:

<?$valid_post_id('1','2','3','4');?>

to

<?php $valid_post_id = array('1','2','3','4');?>