How To Add A Featured Image To WordPress All Posts Screen

How to show the featured image to WordPress "All Posts" admin screen which is useful to see what posts haven't got a thumbnail set.

Featured images, also known as Post Thumbnails, are pictures that symbolise a specific Post, Page, or Custom Post Type. When you design your Theme, you can include the featured image in a variety of places, such as your archive page, header, or above a post in a header.

Enable Featured Image Support

Before the Featured Image interface will be shown on the Edit screen, themes must declare support for the Featured Image function. Support is declared in your theme's functions.php file by including the following code:

add_theme_support('post-thumbnails');

When you enable Featured Images support, the Featured Image meta box will appear on the Edit screens for the relevant content item. If a person cannot see it, they can enable it in their screen settings. The Featured Image meta box is displayed by default in the sidebar of the Edit Post and Edit Page screens.

Adding Featured Image Column to WordPress All Posts View

The featured image thumbnail is added by hooking into the manage_posts_columns action. This action maintains a list of the columns, to add or remove columns, you just need to add or remove the entry from the array. The following snippet will add an Image column to the end of the table. To insert an item at a specific place, you have to use PHP's array_splice  function to insert the item.

function custom_columns($columns) 
{
  $columns['featured_image'] = 'Image';
  return $columns;
}
add_filter('manage_posts_columns' , 'custom_columns');

Now that WordPress knows about the column, we have to add another function to display the image. This is done using the manage_posts_custom_column action. This action runs for each column, and a check on the column allows you to specify the data output. In this case, we are only adding one column, but you can add to it by simply extending the switch statement.

function custom_columns_data($column, $post_id)
{
  switch ( $column ) 
  {
    case 'featured_image':
        echo the_post_thumbnail('thumbnail');
        break;
  }
}
add_action('manage_posts_custom_column', 'custom_columns_data', 10, 2);

Add these code blocks to your themes functions.php or your WordPress plugin file and the featured image will be shown on the WordPress admin post listings pages.