mlp-addon-post-meta.php

<?php # -*- coding: utf-8 -*-
/**
 * Plugin Name: MLP Addon: Sync post meta fields
 * Plugin URI:  https://gist.github.com/toscho/6393c79aacba0983a96a
 * Description: Create a custom field, put it into the MLP translation box, and sync it across the sites.
 * Version:     2015.03.03
 * Required:    4.0
 * Author:      Thomas Scholz <[email protected]>
 * Author URI:  http://toscho.de
 * License:     MIT
 * License URI: http://www.opensource.org/licenses/mit-license.php
 */
class Mlp_Support_Post_Meta_Sync {

	/**
	 * @type string
	 */
	private $meta_key;

	/**
	 * @type array
	 */
	private $send_post_meta = array();

	/**
	 * Set up class variables
	 * 
	 * @param $meta_key
	 */
	public function __construct( $meta_key ) {

		$this->meta_key = $meta_key;

	}

	public function setup() {

		add_action(
			'mlp_translation_meta_box_bottom',
			array( $this, 'show_field' ),
			2,
			3
		);

		add_filter(
			'mlp_pre_save_post_meta',
			array( $this, 'register_meta_fields' ),
			10,
			2
		);

		add_filter(
			'mlp_pre_insert_post_meta',
			array( $this, 'save_meta' ),
			10,
			2
		);
	}

	/**
	 * @wp-hook mlp_translation_meta_box_bottom
	 *
	 * @param WP_Post $post
	 * @param int     $remote_site_id
	 * @param WP_Post $remote_post
	 *
	 * @return void
	 */
	public function show_field(
		WP_Post $post,
		$remote_site_id,
		WP_Post $remote_post = NULL
	) {

		$value = '';

		if ( NULL !== $remote_post ) {
			switch_to_blog( $remote_site_id );
			$value = get_post_meta( $remote_post->ID, $this->meta_key, TRUE );
			restore_current_blog();
		}

		$value = esc_attr( $value );

		printf(
			'
<label for="%1$s_%2$s_id">
	Value for <strong>%1$s</strong>
	<input id="%1$s_%2$s_id" type="text" name="%1$s_%2$s" value="%3$s">
</label><br>',
			$this->meta_key,
			$remote_site_id,
			$value
		);
	}

	public function register_meta_fields( array $post_meta ) {

		if ( ! empty ( $_POST ) ) {

			foreach ( $_POST as $key => $value ) {

				if ( 0 !== strpos( $key, $this->meta_key ) ) {
					continue;
				}

				$m = array();
				preg_match( '~_(\d+)$~', $key, $m );

				if ( ! empty ( $m[ 1 ] ) ) {
					$site_id                          = $m[ 1 ];
					$this->send_post_meta[ $site_id ] = $value;
				} else {
					$post_meta[ $key ] = $value;
				}
			}
		}

		return $post_meta;
	}

	public function save_meta( array $post_meta, array $save_context ) {

		$site_id = $save_context[ 'target_blog_id' ];

		if ( empty ( $this->send_post_meta[ $site_id ] ) ) {
			return $post_meta;
		}

		$post_meta[ $this->meta_key ] = $this->send_post_meta[ $site_id ];

		return $post_meta;
	}
}

add_action( 'mlp_and_wp_loaded', array( new Mlp_Support_Post_Meta_Sync( 'column_left' ), 'setup' ) );
add_action( 'mlp_and_wp_loaded', array( new Mlp_Support_Post_Meta_Sync( 'column_right' ), 'setup' ) );

Hey Biont,
I want to translate post connections with mlp. Do you have an idea, how it works?
When I implement your Post-Meta Add-on, I only have to add the code to the post-translator folder?
Thank you a lot!