Showing feature image in admin post listing

show-meta-data-in-admin-list.php

/**
* WordPress
* Showing feature image in admin post listing
*/

add_filter('manage_posts_columns' , 'ask_custom_columns');
/*add_filter('manage_{post-type-slug}_posts_columns' , 'ask_custom_columns');*/

function ask_custom_columns( $columns ) {
    $columns = array(
        'cb' => '<input type="checkbox" />',
        'featured_image' => 'Feature Image',
        'title' => 'Title',
        'comments' => '<span class="vers"><div title="Comments" class="comment-grey-bubble"></div></span>',
        'date' => 'Date'
     );
    return $columns;
}

add_action( 'manage_posts_custom_column' , 'ask_custom_columns_data', 10, 2 );
/*add_filter('manage_{post-type-slug}_posts_custom_column' , 'ask_custom_columns_data',10,2);*/

function ask_custom_columns_data( $column, $post_id ) {
    switch ( $column ) {
    case 'featured_image':
        the_post_thumbnail( 'thumbnail' );
        break;
    }
}