Add Custom Columns to WP Admin List

PostColumnExtension

/*
    Snipped: Create Custom Post Extension 
    Author: Gkiokan Sali
    Author URL: https://www.gkiokan.net
    Date: 13.03.2017
    Tested on WP: 4.7.3
    License: MIT
    Description: Extend your Admin List Table by custom columns in a easy way.
    Just call the Class in your Plugin with PostcolumnExtension($YourPostType) and you are fine to go.
    The Plugin will hook into the manage_*_posts_columns and will render the specified Column Content,
    - in this case the Thumbnail. Feel free to update the code or yourself.
*/

class PostColumnExtension {
    protected $post_type = null;

    public function __construct($pt=null){
        $this->post_type = $pt;
        add_action('manage_' . $pt . '_posts_columns', [$this, 'posts_columns'], 5);
        add_action('manage_' . $pt . '_posts_custom_column', [$this, 'posts_custom_columns'], 1, 2);
    }

    /*
        Adds Thumbs to the Admin List
    */
    public function posts_columns($defaults){
        $defaults['wps_post_thumbs'] = __('Beitragsbild');        
        return $defaults;
    }


    /*
        Create the Column Content
    */
    public function posts_custom_columns($column_name, $id){
        $c = $column_name;
        if($column_name === 'wps_post_thumbs'){            
            echo "<img src='". get_the_post_thumbnail_url($id) . "' style='width:100%; height:auto; max-width: 140px;'>";
        }
    }
}