WordPress: Child Pages Meta Box For Hierarchial Post Types

wpse-current-child-pages-metabox.php

    <?php
    
    /**
     * Plugin Name: Child Pages Meta Box
     * Description: Child pages meta box for hierarchial post types
     * Author:      Birgir Erlendsson (birgire)
     * Plugin URI:  http://wordpress.stackexchange.com/a/158636/26350
     * Version:     0.0.2
     */
     
    function wpse_current_child_pages_meta_box()
    {
    	$post_types = get_post_types(); 
    	foreach ( $post_types as $post_type )
    	{
    		if( is_post_type_hierarchical( $post_type ) )
    		{
    			add_meta_box(
    				'wpse_child_pages',
    				__( 'Current child pages' ),
    				'wpse_list_current_child_pages',
    				$post_type,
    				'side',
    				'low'
    			);
    		}
    	}
    }
    add_action( 'add_meta_boxes', 'wpse_current_child_pages_meta_box' );
    
    function wpse_list_current_child_pages( $post )
    {
    	$args = array(
    		'child_of'      => $post->ID,
    		'echo'          => 0,
    		'title_li'	=> '',
    		'post_type'	=> $post->post_type,
    		'walker'	=> new WPSE_EditLinks
    	);
    	$style = '<style>.wpse_childpages li {margin-left: 15px;}</style>';
    	$list = wp_list_pages( $args );
    	if( ! $list )
    		$list = sprintf( '<li>%s</li>', __( 'No child pages found!' ) );
    		
    	printf( '%s<ul class="wpse_childpages">%s</li>', $style, $list  );
    }
    
    class WPSE_EditLinks extends Walker_Page 
    {
    	function end_el( &$output, $page, $depth = 0, $args = array() )
    	{		
    		$edit_url  = admin_url( 'post.php?action=edit&post=' . $page->ID );
    		$edit_link = " <a class='dashicons dashicons-edit' title='edit' href='" . esc_url( $edit_url ) . "' target='_blank'></a> ";
    		$output    = str_replace( "><a", ">". $edit_link. "<a", $output );
    		$output   .= "</li>\n";
    	}
    }