ld-dashboard-create-custom-field-course.php

<?php
/*
** Add a custom field on course front end form
*/
function ld_dashboard_course_form_fields_callback( $fields ) {

    /**
    * Add following classes to add fields in specific sections.
    *
    * For 'Main' tab - 'ld-dashboard-form-post-data-tab'
    * For 'Builder' tab - 'ld-dashboard-course-builder-wrapper'
    * For 'Settings' tab - 'ld-dashboard-form-settings-data-tab'
    */

    $new_field = array(
        'key'               => 'field_key', /* (string) Unique identifier for the field. Must begin with 'field_' */
        'label'             => 'Field Label', /* (string) Visible when editing the field value */
        'name'              => 'field_name', /* (string) Used to save and load data. Single word, no spaces. Underscores and dashes allowed */
        'type'              => 'text', /* (string) Type of field (text, textarea, image, etc) */
        'instructions'      => '', /* (string) Instructions for authors. Shown when submitting data */
        'required'          => 0, /* (int) Whether or not the field value is required. Defaults to 0 */
        'conditional_logic' => 0,/* (mixed) Conditionally hide or show this field based on other field's values. 
        Best to use the ACF UI and export to understand the array structure. Defaults to 0 */
        'wrapper'           => array(
            'width' => '',
            'class' => 'custom-learndash-course-form ld-dashboard-form-settings-data-tab', /* This class will define where the field will display */
            'id'    => '',
        ), /* (array) An array of attributes given to the field element */
        'default_value'     => '', /* (mixed) A default value used by ACF if no value has yet been saved */
        'placeholder'       => '', /* (string) A placeholder of the field */
    );

    // To add new field at the top position.
    $field  = array( $new_field );
    $fields = array_merge( $field, $fields );

    // Make sure to enable the newly created field in backend,
    // Go to WB Plugins > LearnDash Dashboard > Field Restriction for enabling the field.
   
    return $fields;
}
add_filter( 'ld_dashboard_course_form_fields', 'ld_dashboard_course_form_fields_callback' , 10, 1 );


 // Add custom meta box programatically in backend
 function wbcom_register_meta_box() {
    add_meta_box(
        'meta-field-id', /* (string) (Required) Meta box ID (used in the 'id' attribute for the meta box). */
        'Meta Box Title', /* (string) (Required) Title of the meta box.*/
        'wbcom_show_custom_meta_box_content',  /* (callable) (Required) Function that fills the box with the desired content. The function should echo its output. */
        'sfwd-courses',            // $page - post type slug where you want to display the meta field in backend
        'normal',                  // $context
        'low'                      // $priority
    );
}
add_action( 'add_meta_boxes', 'wbcom_register_meta_box' );

//Callback function to render meta box content
function wbcom_show_custom_meta_box_content() {
    global $post;
    // Use same string for name attribute as used for ACF 'name' value above 
    ?>
    <input type="text" name="field_name" value="<?php echo get_post_meta( $post->ID, 'field_name', true ); ?>">
    <?php
}

//Save  meta box value
function wbcom_save_post_data_callback( $post_id ) {
    // Used to save meta field value from backend.
    if ( isset( $_POST['field_name'] ) ) {
        update_post_meta( $post_id, 'field_name', sanitize_text_field( $_POST['field_name'] ) );
    }
}
add_action( 'save_post', 'wbcom_save_post_data_callback' );