The view relationship for Flag module only allows you to set a single flag type as a target, which means only one flag type is available on a views row.

My specific use case is adding flag/unflag links to the /admin/content page which I've replaced by a view with the Admin Views module. I ended up digging around quite a bit through Flag module's source code to pop this one out.

The heart of it is in a views field template--one of your choosing. The code is agnostic as long as you have a the $row->nid field, and this specific code filters for just the node entity type, but you could use it for any of the other types readily.

<?php
  $flags = flag_get_flags();
  $links = array();
  foreach ($flags as $flag) {
    if ($flag->entity_type == 'node') {
      $links[] = flag_create_link($flag->name, $row->nid); // get links, if not possible ($flag->access($eid)), returns null.
    }
  }
  $links = array_values(array_filter($links));
?>
<div>
  <ul>
    <?php foreach ($links as $link) : ?>
      <li><?php print $link; ?></li>
    <?php endforeach; ?>
  </ul>
</div>

...and I wanted to stick it in a module rather than a theme, so I implemented this in my module to scan a subdir, templates, rather than shove it into the theme directory. Felt cleaner.

/**
 * Implements hook_views_api().
 *
 * Enabling using templates inside module
 */
function mymodule_views_api() {
  return array(
    'api' => 3,
    'path' => drupal_get_path('module', 'rs_contextual_links'),
    'template path' => drupal_get_path('module', 'rs_contextual_links') . '/templates',
  );
}

What I really wanted to do was implement a preprocess function to override $output for just this field type, but the preprocess function didn't exist without the template file declared. So why split the code up? Anyone know how to do that?