Ytukyg

My code:

add_action( 'woocommerce_before_checkout_form', 'fruit_field' );



function fruit_field( $checkout ) {



  woocommerce_form_field( 'fruit', array(

      'type'          => 'select',

      'required'      => true,

      'options'       => array(

        'apple'       => __('Apple'),

        'banana'      => __('Banana'),

        'watermelon'  => __('Watermelon'),

        'other'       => __('Other'),

      ),

      'class'         => array('my-class'),

      'label'         => __('Best fruit?'),

      ), $checkout->get_value( 'fruit' ));

}

And the validation:

add_action('woocommerce_checkout_process', 'process_checkout');



function process_checkout() {

  if ($_POST['fruit'] === null) {

    wc_add_notice( __( 'No fruits?' ), 'error' );

  }

}

After submitting the form, it always displays my custom error "No fruits?", no matter what was selected. Is $_POST['fruit'] somehow not available in the process_checkout function?

You can not use custom checkout fields in woocommerce_before_checkout_form hook as your field is outside the checkout form, and it is not posted on submit.

Instead you should use woocommerce_checkout_before_customer_details action hook instead:

add_action( 'woocommerce_checkout_before_customer_details', 'fruit_custom_checkout_field' );

function fruit_custom_checkout_field() {



    woocommerce_form_field( '_fruit', array(

        'type'     => 'select',

        'label'    => __('Best fruit?'),

        'class'    => array('my-fruit'),

        'required' => true,

        'options'  => array(

            ''          => __('Chose a fruit'),

            'Apple'      => __('Apple'),

            'Banana'     => __('Banana'),

            'Watermelon' => __('Watermelon'),

            'Other'      => __('Other'),

        ),

    ), WC()->checkout->get_value('_fruit') );

}



add_action('woocommerce_checkout_process', 'process_fruit_custom_checkout_field');

function process_fruit_custom_checkout_field() {

    if (isset($_POST['_fruit']) && empty($_POST['_fruit']) ) {

        wc_add_notice( __( 'please choose a "fruits"' ), 'error' );

    }

}



// Save the custom checkout field in the order meta

add_action( 'woocommerce_checkout_create_order', 'save_fruit_custom_field_as_meta_data', 10, 2 );

function save_fruit_custom_field_as_meta_data( $order, $data ) {

    if (isset($_POST['_fruit']) && ! empty($_POST['_fruit']) ) {

        $order->update_meta_data('_custom_field', esc_attr( $_POST['_fruit'] ) );

    }

}

Code goes in function.php file of your active child theme (or active theme). Tested and works.