Example programmatic registration of Advanced Custom Fields fields

acf-field-registration-example.php

<?php
/**
 * Example programmatic registration of Advanced Custom Fields fields
 * 
 * @see http://www.advancedcustomfields.com/resources/register-fields-via-php/
 */

function register_custom_acf_fields() {
	if ( function_exists( 'acf_add_local_field_group' ) ) {

		// ACF Group: People
		acf_add_local_field_group( array (
			'key'      => 'group_person_details',
			'title'    => 'Person Details',
			'location' => array (
				array (
					array (
						'param'    => 'post_type',
						'operator' => '==',
						'value'    => 'person',
					),
				),
			),
			'menu_order'            => 0,
			'position'              => 'normal',
			'style'                 => 'default',
			'label_placement'       => 'top',
			'instruction_placement' => 'label',
			'hide_on_screen'        => '',
		) );

		// First name
		acf_add_local_field( array(
			'key'          => 'field_first_name',
			'label'        => 'First Name',
			'name'         => 'first_name',
			'type'         => 'text',
			'parent'       => 'group_person_details',
			'instructions' => '',
			'required'     => 1,
		) );

		// Middle name
		acf_add_local_field( array(
			'key'          => 'field_middle_name',
			'label'        => 'Middle Name',
			'name'         => 'middle_name',
			'type'         => 'text',
			'parent'       => 'group_person_details',
			'instructions' => '',
			'required'     => 0,
		) );

		// Last name
		acf_add_local_field( array(
			'key'          => 'field_last_name',
			'label'        => 'Last Name',
			'name'         => 'last_name',
			'type'         => 'text',
			'parent'       => 'group_person_details',
			'instructions' => '',
			'required'     => 1,
		) );

		// Image
		acf_add_local_field( array(
			'key'           => 'field_image',
			'label'         => 'Image',
			'name'          => 'image',
			'type'          => 'image',
			'parent'        => 'group_person_details',
			'instructions'  => '',
			'required'      => 0,
			'return_format' => 'array',
			'preview_size'  => 'thumbnail',
			'library'       => 'all',
			'min_width'     => 0,
			'min_height'    => 0,
			'max_width'     => 0,
			'max_height'    => 0,
		) );

		// Office
		acf_add_local_field( array(
			'key'          => 'field_office',
			'label'        => 'Office',
			'name'         => 'office',
			'type'         => 'text',
			'parent'       => 'group_person_details',
			'instructions' => '',
			'required'     => 0,
		) );

		// E-mail
		acf_add_local_field( array(
			'key'          => 'field_email',
			'label'        => 'E-mail',
			'name'         => 'email',
			'type'         => 'email',
			'parent'       => 'group_person_details',
			'instructions' => '',
			'required'     => 0,
		) );

		// Office Phone
		acf_add_local_field( array(
			'key'          => 'field_phone',
			'label'        => 'Phone',
			'name'         => 'phone',
			'type'         => 'text',
			'parent'       => 'group_person_details',
			'instructions' => '',
			'required'     => 0,
		) );

		// Affiliation
		acf_add_local_field( array(
			'key'             => 'field_affiliation',
			'label'           => 'Affiliation',
			'name'            => 'affiliation',
			'type'            => 'taxonomy',
			'parent'          => 'group_person_details',
			'instructions'    => '',
			'required'        => 0,
			'taxonomy'        => 'affiliation',
			'field_type'      => 'multi_select',      // UI (checkbox, multi-select, select, radio)
			'allow_null'      => 0,             // Can select a blank value
			'load_save_terms' => 1,             // Persist using term relationships table
			'return_format'   => 'object',      // or 'object'
			'add_term'        => 0,             // Can the user add new terms?
		) );
	}
}

add_action( 'init', 'register_custom_acf_fields' );

Function details https://docs.wpdebuglog.com/plugin/advanced-custom-fields/5.8.8/function/acf_add_local_field_group/

How do you add fields to different groups without redefining fields each time?

I just had the same question after looking at the docs. The answer is: you define the fields as variables first, then assign those field variables to the group. Consider the following...

// Define a field
$field1 = array(
    'key' => 'field_1',
    'label' => 'Title',
    'name' => 'title',
    'type' => 'text'
  );
// Define another field
  $field2 = array(
    'key' => 'field_2',
    'label' => 'Sub Title',
    'name' => 'sub_title',
    'type' => 'text'
  );

// Add a field group
acf_add_local_field_group(array(
    'key' => 'group_1',
    'title' => 'My Group',
    'fields' => array ($field1, $field2), // Assign those field vars
    'location' => array (
      array (
        array (
          'param' => 'post_type',
          'operator' => '==',
          'value' => 'page',
        ),
      ),
    ),
  ));

I hope that helps folks.