Wordpress中Widget表单函数中的中继器字段

public function form( $instance ) {
    $title = ! empty( $instance['title'] ) ? $instance['title'] : '';
    // 其他表单字段
    // ...
    $relay_field = esc_attr( $this->get_field_name( 'relay' ) );
    ?>
    <p>
        <label for="<?php echo $relay_field; ?>"><?php _e( 'Relay:', 'text_domain' ); ?></label>
        <input class="widefat" id="<?php echo $relay_field; ?>" name="<?php echo $relay_field; ?>" type="text" value="<?php echo esc_attr( $instance['relay'] ); ?>">
    </p>
    <?php
}

public function update( $new_instance, $old_instance ) {
    $instance = array();
    $instance['title'] = ( ! empty( $new_instance['title'] ) ) ? sanitize_text_field( $new_instance['title'] ) : '';
    // 其他字段的处理
    // ...
    $instance['relay'] = ( ! empty( $new_instance['relay'] ) ) ? sanitize_text_field( $new_instance['relay'] ) : '';

    return $instance;
}