Shows how to set up a click-to-sort header for a Participants Database list table template

pdb-list-sort-columns.php

<?php
/**
 * @version 1.0
 * 
 * template for participants list shortcode output
 *
 * this demonstrates how to add a click-to-sort header to the list
 *
 */

// add the filter handler that places the sorting links on the header titles
add_filter('pdb-list_header_title', 'xnau_list_column_sort_link', 10, 3 );

 /**
   *  
   * @param string $title
   * @param PDb_Form_Field_Def $field
   * @param array $filter the current list filter
   * @return string title
   */
  function xnau_list_column_sort_link( $title, $field, $filter )
  {
    if ( !$field->is_sortable() )
    {
      return $title;
    }
    
    // place the request values into the $get_array variable
    parse_str( $_SERVER['QUERY_STRING'], $get_array );
    
    // get the link back to the list
    global $post;
    $base_url = get_permalink( $post->ID );
    
    $ascdesc = 'ASC';
    if ( isset($get_array['sortBy']) && $field->name() === $get_array['sortBy'] && isset( $get_array['ascdesc'] ) )
    {
      // we're getting the opposite of the submitted sort direction
      $ascdesc = stripos( $get_array['ascdesc'], 'ASC' ) !== false ? 'DESC' : 'ASC';
    }
    
    $arg_array = array(
        'search_field' => xnau_get_input_value( 'search_field' ) ? : 'searchfield',
        'value' => xnau_get_input_value( 'value' ) ? : '*',
        'sortBy' => $field->name(),
        'ascdesc' => $ascdesc,
    );
    
    $title = sprintf( '<a href="%1$s">%2$s%3$s</a>', add_query_arg( $arg_array, $base_url ), $title, xnau_sort_icon( $ascdesc ) );
    
    return $title;
  }
  
  /**
   * provides the sort icon
   * 
   * @param string $ascdesc
   * @return string icon HTML
   */
  function xnau_sort_icon( $ascdesc )
  {
    return sprintf( '<span class="sort-arrow-%s"></span>', ( $ascdesc === 'ASC' ? 'down' : 'up' ) );
  }
  
  /**
   * supplies the requested value from the input
   * 
   * @param string $name of the value
   * @return the value or bool false if not found
   */
  function xnau_get_input_value( $name )
  {
    $inputval = filter_input( INPUT_POST, $name, FILTER_DEFAULT, array('flags' => FILTER_NULL_ON_FAILURE ) );
    
    if ( $inputval === false )
    {
      $inputval = filter_input( INPUT_GET, $name, FILTER_DEFAULT, array('flags' => FILTER_NULL_ON_FAILURE ) );
    }
    
    return $inputval;
  }

?>
<div class="wrap <?php esc_attr_e( $this->wrap_class ) ?>" id="<?php esc_attr_e( $this->list_anchor ) ?>">
  <?php
  /*
   * SEARCH/SORT FORM
   *
   * the search/sort form is only presented when enabled in the shortcode.
   *
   */
  $this->show_search_sort_form();

  /* LIST DISPLAY */
  /*
   * NOTE: the container for the list itself (excluding search and pagination 
   * controls) must have a class of "list-container" for AJAX search/sort to 
   * function
   */
  ?>
  
  <style>
    .sort-arrow-up::after {
      content: '\25B2';
    }
    .sort-arrow-down::after {
      content: '\25BC';
    }
  </style>
  <table class="wp-list-table widefat fixed pages list-container" >

    <?php if ( has_action( 'pdb-prepend_to_list_container_content' ) ) : ?>
      <caption>
        <?php do_action( 'pdb-prepend_to_list_container_content' ) ?>
        <?php $this->print_list_count( '<div class="%s"><span class="list-display-count">' ) ?>
      </caption>
    <?php else : ?>
      <?php
      /* print the count if enabled in the shortcode
       * 
       * the tag wrapping the count statment can be supplied in the function argument, example here
       */
      $this->print_list_count( '<caption class="%s" ><span class="list-display-count">' );
      ?>
    <?php endif ?>

    <?php if ( $record_count > 0 ) : // print only if there are records to show ?>

      <thead>
        <tr>
          
          <?php
          /*
           * this function prints headers for all the fields
           * replacement codes:
           * %2$s is the form element type identifier
           * %1$s is the title of the field
           */
          $this->print_header_row( '<th class="%2$s" scope="col">%1$s</th>' );
          ?>
        </tr>
      </thead>

      <tbody>
          <?php while ( $this->have_records() ) : $this->the_record(); // each record is one row  ?>
          <tr>
    <?php while ( $this->have_fields() ) : $this->the_field(); // each field is one cell  ?>

              <td class="<?php esc_attr_e( $this->field->name() ) ?>-field">
                
      <?php $this->field->print_value() ?>
              </td>

          <?php endwhile; // each field  ?>
          </tr>
  <?php endwhile; // each record  ?>
      </tbody>

<?php else : // if there are no records  ?>

      <tbody>
        <tr>
          <td><?php if ( $this->is_search_result ) echo wp_kses_post( Participants_Db::plugin_setting('no_records_message') ) ?></td>
        </tr>
      </tbody>

<?php endif; // $record_count > 0  ?>

  </table>
  <?php
  /*
   * this shortcut function presents a pagination control with default layout
   */
  $this->show_pagination_control();
  ?>
</div>

Place this template in the Participants Database template location:

wp_content/participants-database-templates/pdb-list-sort-columns.php

Then call it in the shortcode like this:

[pdb_list search=true template=sort-columns]

This only works for fields that are maked as "sortable" so you should check the field definitions.