How to add a Custom Column in WordPress with OOP | http://www.ibenic.com/add-custom-column-wordpress-oop/

action1.php

<?php
// Action Hook to add column value for posts
add_action( 'manage_posts_custom_column' , 'your_function', 10, 2 );

action2.php

<?php
// Action Hook to add column value for custom post types
add_action( 'manage_{$post_type}_posts_custom_column' , 'your_function', 10, 2 );

action3.php

<?php
// Action Hook to add columns for posts
add_action( 'manage_pages_custom_column' , 'your_function', 10, 2 );

add_column.php

<?php

class WordPressColumn {
    	// ...
    
  	/**
	 * Add the column to the columns array
	 * @param array $columns
	 */
	public function add_column( $columns ) {
		$columns[ $this->options['column_key'] ] = $this->options['column_title'];
		return $columns;
	}
}

class1.php

<?php

class WordPressColumn {
  
  	/**
	 * Default definitions
	 * @var array
	 */
	public $defaults = array(
		'post_type' => 'post',
		'column_key' => '',
		'column_title' => '',
		'column_display' => 'column_key'
		);

	/**
	 * Container of our options for the column
	 * @var array
	 */
	public $options = array();
	
}

class2.php

<?php

class WordPressColumn {
  
  	// ...
  
  	/**
	 * Merge added options with the defaults. If the column key is not defined throw and exception.
	 * If we do not have a title for the column, create one from the column key
	 * @param array $options 
	 */
	public function __construct( $options ){
	
		$this->options = array_merge( $this->defaults, $options );
	
		if( $this->options['column_key'] == '' ){
			$message = __( 'Column key is not defined', 'yourtextdomain' );
			throw new Exception( $message );
		}
	
		if( $this->options['column_title'] == '' ) {
			$this->options['column_title'] = ucfirst( $this->options['column_key'] );
		}
	}
	
}

class3.php

<?php

class WordPressColumn {
    	// ...
    
  	/**
	 * Attach this column by using WordPress filters and actions
	 * If the post type is different from 'post' and 'page' then add a new word to filters and actions to dynamically target our columns
	 * If the post type is a page, then change the for_type variable so that the column is added to the pages section
	 * @return void 
	 */
	public function attach() {
		$post_type = '';
		if( $this->options['post_type'] != 'post' && $this->options['post_type'] != 'page'   ){
			$post_type = '_' . $this->options['post_type'];
		}

		$for_type = 'posts';
		if( $this->options['post_type'] == 'page' ) {
			$for_type = 'pages';
		}
		add_filter('manage' . $post_type . '_' . $for_type . '_columns' , array( $this, 'add_column' ) );

		add_action( 'manage' . $post_type . '_' . $for_type . '_custom_column', array( $this, 'column_data' ), 10, 2);

	}
}

data_column.php

<?php

class WordPressColumn {
    	// ...
    
    /**
     * Render a column
     * @param  string $column  Column slug/key
     * @param  string $post_id 
     * @return void      
     */
    public function column_data( $column, $post_id ){
    
    	if( $column == $this->options['column_key'] ){
    		if( $this->options['column_display'] == 'column_key' ){
    			echo get_post_meta( $post_id, $this->options['column_key'], true );
    		} else {
    			$function_name = $this->options['column_display'];
    			call_user_func_array($function_name, array( $post_id, $this->options['column_key'] ) );
    		}
    	}
    }
}

example1.php

<?php

function render_user_by_id( $post_id, $column_key) {
	$user_id = get_post_meta( $post_id, $column_key, true );
	$userdata = get_userdata( $user_id );
	echo $userdata->user_login;
}

$column = new WordPressColumn( array(
			'column_key' => '_edit_last',
			'column_title' => __( 'Last Edited', 'yourtextdomain' ),
			'column_display' => 'render_user_by_id'
      ));

$column->attach();

example2.php

<?php

function render_user_by_id( $post_id, $column_key) {
	$user_id = get_post_meta( $post_id, $column_key, true );
	$userdata = get_userdata( $user_id );
	echo $userdata->user_login;
}

$column1 = new WordPressColumn( array(
	'column_key' => '_edit_last',
	'column_title' => __( 'Last Edited', 'yourtextdomain' ),
	'column_display' => 'render_user_by_id'
	));

$columns = new WordPressColumns ( array( 
	$column1
	));

$columns->add_columns();

example3.php

<?php

function render_user_by_id( $post_id, $column_key) {
	$user_id = get_post_meta( $post_id, $column_key, true );
	$userdata = get_userdata( $user_id );
	echo $userdata->user_login;
}

$columns = new WordPressColumns ( array(

		array(
			'column_key' => '_edit_last',
			'column_title' => __( 'Last Edited', 'yourtextdomain' ),
			'column_display' => 'render_user_by_id'
			),
	));

$columns->add_columns();

factory.php

<?php

class WordPressColumns {
  
	/**
	 * All columns
	 */
	public $columns = array();

	public function __construct( $columns ) {
		$this->columns = $columns;
	}

	public function add_columns() {
		foreach ( $this->columns as $column ) {
			$column->attach();
		}
	}


}

factory2.php

<?php

class WordPressColumns {

  public $columns = array();
  
  public function __construct( $columns ) {
  	$this->columns = $columns;
  }
  
  public function add_columns() {
  	foreach ( $this->columns as $column ) {
  
  		$the_column = new WordPressColumn( $column );
  		$the_column->attach();
  		
  	}
  }

}

filter1.php

<?php
// Filter Hook to add columns for posts
add_filter('manage_posts_columns' , 'your_function');

filter2.php

<?php
// Filter Hook to add columns for custom post types
// {$post_type} is replaced by custom post type slug
add_filter('manage_{$post_type}_posts_columns' , 'your_function');

filter3.php

<?php
// Filter Hook to add columns for pages
add_filter('manage_pages_columns' , 'your_function');