WordPress CMB2 Base

cmb2.php

<?php
/**
 * Reason for CMB2 box
 */
function cmb2_admin_init() {
	$prefix = 'add_prefix_here';

	// Create the box.
	$cmb2 = \new_cmb2_box(
		array(
			'id'           => '[CHANGEME-id]',
			'title'        => __( '[CHANGEME-title]', '[CHANGEME-localization]' ),
			'object_types' => array(
				'page',
			),
			'context'      => 'normal',
			'priority'     => 'default',
			'show_names'   => true,
			'show_on'      => array(
				'key'   => 'page-template',
				'value' => array(
					'page-templates/[CHANGEME-page-template].php',
				),
			),
		)
	);

	// Add fields below.

}
add_action( 'cmb2_admin_init', __NAMESPACE__ . '\\cmb2_admin_init' );