Add sticky functionality to CPT's

sticky.php

<?php

add_action( 'admin_init', 'cpt_sticky_add_meta_box' );
add_filter( 'the_posts', 'cpt_sticky_at_top' );
add_filter( 'post_limits', 'fix_post_count', 10, 2 );

function cpt_sticky_meta() { ?>
  <input id="super-sticky" name="sticky" type="checkbox" value="sticky" <?php checked( is_sticky() ); ?> /> <label for="super-sticky" class="selectit"><?php _e( 'Stick this to the top' ) ?></label><?php
}

function cpt_sticky_add_meta_box() {
  if( ! current_user_can( 'edit_others_posts' ) )
    return;

  $sticky_post_types = array( 'news', 'press_release'); //Replace this with your cpt names

  foreach( $sticky_post_types as $post_type )
    add_meta_box( 'cpt_sticky_meta', __( 'Sticky' ), 'cpt_sticky_meta', $post_type, 'side', 'default' );
}

function cpt_sticky_at_top( $posts ) {
 
  // apply it on the archives only
  if ( is_main_query() && !is_single() ) {
    global $wp_query;
 
    $sticky_posts = get_option( 'sticky_posts' );
    $num_posts = count( $posts );
    $sticky_offset = 0;
    // Find the sticky posts
    for ($i = 0; $i < $num_posts; $i++) {
 
      // Put sticky posts at the top of the posts array
      if ( in_array( $posts[$i]->ID, $sticky_posts ) ) {
        $sticky_post = $posts[$i];
 
        // Remove sticky from current position
        array_splice( $posts, $i, 1 );
          
        // Move to front, after other stickies
        array_splice( $posts, $sticky_offset, 0, array($sticky_post) );
        $sticky_offset++;
 
        // Remove post from sticky posts array
        $offset = array_search($sticky_post->ID, $sticky_posts);
        unset( $sticky_posts[$offset] );
      }
    }
  }
 
    return $posts;
}

function fix_post_count( $limit, $query ) {

  if ( !is_admin() && !is_single() ) {
    $sticky_posts = get_option( 'sticky_posts' );
    $i = 0;
    foreach( $sticky_posts as $post ) {
      $postObj = get_post($post);
      if ( isset( $query->query_vars['post_type'] ) ) {
        if ( $query->query_vars['post_type'] == $postObj->post_type ) {
          $i++;
        }
      } 
    }
    $oldLimit = $query->query_vars['posts_per_page'];
    $newLimit = ($oldLimit + $i);

    return 'LIMIT 0, ' . $newLimit;

  }
  return $limit;
}

?>