events.php

<?php
add_action('init', 'event_list_init');             // register event posts
add_action('admin_init', 'add_events_metaboxes');  // register metaboxes

function event_list_init(){

    $labels = array(
        'name'                  => _x( 'Events', 'post type general name' ),
        'singular_name'         => _x( 'Event', 'post type singular name' ),
        'menu_name'             => _x( 'Events List', 'admin menu' ),
        'name_admin_bar'        => _x( 'Events List', 'add new on admin bar' ),
        'add_new_item'          => __( 'Add New Event' ),
        'new_item'              => __( 'New Event' ),
        'edit_item'             => __( 'Edit Event' ),
        'view_item'             => __( 'View Event' ),
        'all_items'             => __( 'All Events' ),
        'search_items'          => __( 'Search Events' ),
        'not_found'             => __( 'No Events found.' ),
        'not_found_in_trash'    => __( 'No Events found in Trash.' )
    );

    $args   = array(
        'labels'                => $labels,
        'description'           => __( 'Create Events' ),
        'public'                => true,
        'publicly_queryable'    => true,
        'show_ui'               => true,
        'show_in_menu'          => true,
        'query_var'             => true,
        'rewrite'               => array( 'slug' => 'event' ),
        'capability_type'       => 'post',
        'has_archive'           => true,
        'hierarchical'          => true,
        'menu_position'         => 6,
        'menu_icon'             => 'dashicons-calendar-alt',
        'supports'              => array( 'title', 'editor', 'author', 'thumbnail', 'excerpt', 'comments' )
    );

    register_post_type('events',$args);

}

function add_events_metaboxes(){
   new eventsListMetaBox();
}

class eventsListMetaBox{
    /*
     * Constructor that creates the meta box
     */
    public  function  __construct(){
        /**
         * Render and Add form meta box
         */
        add_meta_box('wpt_events_date', 'Events Date', array($this, 'fisa_events_date'), 'events', 'side', 'high');

        /**
         * Save Date from and to as meta key
         */
        add_action('save_post',array($this, 'fisa_events_date_save'),1,2);
    }

    /**
     * Render Form for Events date
     */
    function fisa_events_date() {

        global $post;

        // Add an nonce field so we can check for it later.
        wp_nonce_field( 'events_date_fromto', 'events_datefromto_nonce' );



        // Echo out the field
        echo '<label for="_fisa_date_from">Date From</label>';
        echo '<input id="fisa-event-datefrom" type="text" name="_fisa_date_from"  class="widefat" />';
        echo '<br/><br/>';
        echo '<label for="_fisa_date_to">Date To</label>';
        echo '<input id="fisa-event-dateto" type="text" name="_fisa_date_to" class="widefat" />';

    }

    /**
     * Meta key actual database insertion
     */
    function fisa_events_date_save($post_id){

        //Prepare and sanitize the data before saving it
        $events_date =  array(
                            sanitize_text_field( $_POST['_fisa_date_from']),
                            sanitize_text_field($_POST['_fisa_date_to'])
                        );

        update_post_meta($post_id, '_fisa_events_date', $events_date);


    }
}