The beginning of a class to create + save meta boxes + fields.

olab-class-meta-box.php

<?php

class Olab_Meta_Box {

    public $id, $title, $meta_box;

    /** An array of elements to be rendered in the meta box */
    public $elements = array();

    /** An array of repeatable elements to be rendered in the meta box */
    public $repeaters = array();

    /** The prefix for all meta fields: ie omlb[my-element] */
    public $prefix = 'olmb';

    /** The size of image to display in the meta box on upload */
    public $image_size = 'medium';


    /** Set default variables */
    public function __construct( $id, $title, $args = array() ) {
        $defaults = array(
            'callback'  => array( $this, 'meta_box_callback' ),
            'post_type' => 'post',
            'context'   => 'normal',
            'priority'  => 'high',
        );
        $this->id       = $id;
        $this->title    = $title;
        $this->meta_box = wp_parse_args( $args, $defaults );
    }


    /** Let's get this party started! */
    public function render() {
        global $pagenow;
        // print_r( $pagenow );
        add_action( 'add_meta_boxes', array( $this, 'add_the_meta_box' ) );
        add_action( 'save_post', array( $this, 'save_post_meta' ), 10, 2 );
        if ( 'post-new.php' == $pagenow || 'post.php' == $pagenow )
            add_action( 'admin_enqueue_scripts', array( $this, 'load_admin_js' ) );
    }


    /** Register the metabox */
    public function add_the_meta_box() {
        add_meta_box(
            $this->id,
            $this->title,
            $this->meta_box['callback'],
            $this->meta_box['post_type'],
            $this->meta_box['context'],
            $this->meta_box['priority']
        );
    }


    /** Add an element to the metabox */
    public function add_element( $type, $label, $id, $name = false, $placeholder = '' ) {
        $element               = new StdClass;
        $element->type         = $type;
        $element->label        = $label;
        $element->name         = ( false === $name ) ? $id : $name;
        $element->placeholder  = $placeholder;
        $this->elements[ $id ] = $element;

        return $this;
    }


    /** Add a wp_editor instance to the metabox */
    public function add_wp_editor( $id, $name, $settings = array() ) {
        $element               = new StdClass;
        $element->type         = 'wp_editor';
        $element->name         = ( false === $name ) ? $id : $name;
        $element->settings     = $settings;
        $this->elements[ $id ] = $element;

        return $this;
    }


    /** Add some repeatable fields to the meta box */
    public function add_repeater( $name ) {
        $this->repeaters[] = $name;

        return $this;
    }


    /** Render the metabox element */
    private function _render_element( $id, $attr ) {
        $value = $this->olab_get_meta( $attr );

        switch ( $attr->type ) {

            case 'email'    :
            case 'text'     :
            case 'tel'      :
            case 'password' :
            case 'url'      :

                $element = "<label for='$id'>{$attr->label}</label>\n";
                $element .= "<input type='{$attr->type}' value='$value' id='$id' name='" . $this->prefix . "[" . $attr->name . "]' placeholder='$attr->placeholder'>\n";

                break;

            case 'textarea' :

                $element = "<label for='$id'>{$attr->label}</label>\n";
                $element .= "<textarea id='$id' name='" . $this->prefix . "[" . $attr->name . "]'>$value</textarea>\n";

                break;

            case 'wp_editor' :

                $attr->settings['textarea_name'] = $this->prefix . '[' . $attr->name . ']';
                // Note that the ID that is passed to the wp_editor() function can only be composed of lower-case letters. No underscores, no hyphens. Anything else will cause the WYSIWYG editor to malfunction. See http://codex.wordpress.org/Function_Reference/wp_editor
                ob_start();
                $element = wp_editor( $value, $id, $attr->settings );
                ob_end_flush();

                break;

            case 'uploader' :

                $element = "<a href='#' data-id='$id' class='button olab-uploader-trigger'>" . __( 'Upload', 'mim' ) . '</a>';
                $element .= "<input type='hidden' id='$id' name='" . $this->prefix . "[" . $attr->name . "]'>";
                if ( '' != $value ) {
                    $img = wp_get_attachment_image_src( $value, $this->image_size );
                    $element .= "<img src='{$img[0]}'>";
                }
                break;

        }
        return $element;
    }


    /** Render metabox */
    public function meta_box_callback() {
        wp_nonce_field( basename( __FILE__ ), 'olab_meta_box_nonce' );

        foreach ( $this->elements as $id => $attr ) { ?>
            <div class="element-container">
                <?php echo $this->_render_element( $id, $attr ); ?>
            </div>
        <?php }
    }



    /** Save the meta */
    public function save_post_meta( $post_id, $post ) {
        if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE )
            return $post_id;

        if ( is_int( wp_is_post_autosave( $post_id ) ) )
            return;

        if ( ! current_user_can( 'edit_post', $post_id ) )
            return $post_id;

        if ( ! isset( $_POST[ $this->prefix ] ) )
            return $post_id;

        // die( var_dump( $_POST[ $this->prefix ] ) );

        foreach ( $_POST[ $this->prefix ] as $key => $val ) {

            $meta_key = '_' . $this->prefix . '_' . $key;
            update_post_meta( $post_id, $meta_key, sanitize_text_field( $val ) );

        }
    }


    /** Enqueue the media loader & my JS*/
    function load_admin_js() {
        wp_enqueue_media();
        wp_enqueue_script( 'olab-meta-box-js',  get_bloginfo( 'template_directory' ) . '/includes/olab-meta-box.js', array( 'jquery' ) );
        // wp_localize_script( 'olab-admin-js', 'jsGlobals', $jsglobals );
    }


    /** Get individual post meta */
    public function olab_get_meta( $element, $default = '' ) {
        global $post;

        $meta_key = '_' . $this->prefix . '_' . $element->name;
        $meta = get_post_meta( $post->ID, $meta_key, true );

        if ( ! $meta )
            $meta = $default;

        return $meta;
    }


    /** Get all post meta */
    public function get_all_post_meta() {
        $meta_array = array();

        foreach( $this->elements as $element ) {
            $meta_array[] = olab_get_meta( $element );
        }

        return $meta_array();
    }


}