Multi checkbox fields in Woocommerce backend

Solution 1:

2021 Update

2021 Update - Solved issues with:
• in_array() where 2nd argument was a string on start*.
• $thepostid as in some cases it was empty.

That is possible creating a custom function this way:

// New Multi Checkbox field for woocommerce backend
function woocommerce_wp_multi_checkbox( $field ) {
    global $thepostid, $post;

    if( ! $thepostid ) {
        $thepostid = $post->ID;
    }

    $field['value'] = get_post_meta( $thepostid, $field['id'], true );

    $thepostid              = empty( $thepostid ) ? $post->ID : $thepostid;
    $field['class']         = isset( $field['class'] ) ? $field['class'] : 'select short';
    $field['style']         = isset( $field['style'] ) ? $field['style'] : '';
    $field['wrapper_class'] = isset( $field['wrapper_class'] ) ? $field['wrapper_class'] : '';
    $field['value']         = isset( $field['value'] ) ? $field['value'] : array();
    $field['name']          = isset( $field['name'] ) ? $field['name'] : $field['id'];
    $field['desc_tip']      = isset( $field['desc_tip'] ) ? $field['desc_tip'] : false;

    echo '<fieldset class="form-field ' . esc_attr( $field['id'] ) . '_field ' . esc_attr( $field['wrapper_class'] ) . '">
    <legend>' . wp_kses_post( $field['label'] ) . '</legend>';

    if ( ! empty( $field['description'] ) && false !== $field['desc_tip'] ) {
        echo wc_help_tip( $field['description'] );
    }

    echo '<ul class="wc-radios">';

    foreach ( $field['options'] as $key => $value ) {

        echo '<li><label><input
                name="' . esc_attr( $field['name'] ) . '"
                value="' . esc_attr( $key ) . '"
                type="checkbox"
                class="' . esc_attr( $field['class'] ) . '"
                style="' . esc_attr( $field['style'] ) . '"
                ' . ( is_array( $field['value'] ) && in_array( $key, $field['value'] ) ? 'checked="checked"' : '' ) . ' /> ' . esc_html( $value ) . '</label>
        </li>';
    }
    echo '</ul>';

    if ( ! empty( $field['description'] ) && false === $field['desc_tip'] ) {
        echo '<span class="description">' . wp_kses_post( $field['description'] ) . '</span>';
    }

    echo '</fieldset>';
}

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

Related: Multi Select fields in Woocommerce backend

Usage example (for a simple product):

// Add custom multi-checkbox field for product general option settings
add_action( 'woocommerce_product_options_general_product_data', 'add_custom_settings_fields', 20 );
function add_custom_settings_fields() {
    global $post;

    echo '<div class="options_group hide_if_variable"">'; // Hidding in variable products

    woocommerce_wp_multi_checkbox( array(
        'id'    => '_custom_level',
        'name'  => '_custom_level[]',
        'label' => __('Levels', 'woocommerce'),
        'options' => array(
            'MBO'   => __( 'MBO', 'woocommerce' ),
            'HBO'   => __( 'HBO', 'woocommerce' ),
            'WO'    => __( 'WO', 'woocommerce' )
        )
    ) );

    echo '</div>';
}

// Save custom multi-checkbox fields to database when submitted in Backend (for all other product types)
add_action( 'woocommerce_process_product_meta', 'save_product_options_custom_fields', 30, 1 );
function save_product_options_custom_fields( $post_id ){
    if( isset( $_POST['_custom_level'] ) ){
        $post_data = $_POST['_custom_level'];
        // Data sanitization
        $sanitize_data = array();
        if( is_array($post_data) && sizeof($post_data) > 0 ){
            foreach( $post_data as $value ){
                $sanitize_data[] = esc_attr( $value );
            }
        }
        update_post_meta( $post_id, '_custom_level', $sanitize_data );
    }
}

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

The selected values are correctly saved and displayed. For info the value is an array.