A skeleton for ACF-enabled widgets

widget-skeleton.php

<?php
/**
 * CTA Widget
 *
 * @package _s
 */

class CTA_Widget extends WP_Widget {
  /**
   * Constructor
   */
  public function __construct() {
    $widget_args = array(
      'classname' => 'widget-cta',
      'description' => __( 'CTA widget with title, text and button.', '_s' )
    );
    parent::__construct( 'cta_widget', __( 'CTA Widget', '_s' ), $widget_args );
  }

  /**
   * Display
   */
  public function widget( $args, $instance ) {
    // get the widget ID
    // @link https://goo.gl/X1HGhg
    $wid = 'widget_' . $args['widget_id']; ?>

    <section class="widget widget-cta">
      <?php
      /* Title */
      if ( get_field( 'widget_title', $wid ) ) { ?>
        <h2 class="widget-title widget-cta__title">
          <?php the_field( 'widget_title', $wid ); ?>
        </h2>
      <?php }
      ?>
    </section>
  <?php }

  /**
   * Form
   */
  public function form( $instance ) {}
}

/**
 * Register
 */
function _s_register_cta_widget() {
  register_widget( 'CTA_Widget' );
}
add_action( 'widgets_init', '_s_register_cta_widget' );