How to control metatag module's tags from a page callback?

Question

I have some pages which are created by page callback functions. I'm using the metatag module. I'm on D7

I need to control the metatags output (specifically the description/og:description).

This documentation looks like it would have been useful, but is empty: https://www.drupal.org/docs/7/modules/metatag/howto-assign-meta-tags-to-specific-non-entity-pages-d7

Thanks.

Answer 1

metatags has its own submodule for this, just enable 'Metatag: Context (metatag_context)'

then it appears in 'Add reaction' as 'Metadata'

Answer 2

There's a hook for that. Here's my implementation.

<?php

function mymodule_some_page_callback() {
  global $metatagOverrides;
  // ... generate your page ...

  $metatagOverrides = [
    'og:image' => 'https://example.org/the-image.jpg',
    'og:description' => 'Some description',
    ...
  ];

  return $thePage;
}

function mymodule_metatag_metatags_view_alter(&$output, $instance, $options) {
if (!empty($metatagOverrides)) {
  foreach ($metatagOverrides as $tagname => $value) {
    if (array_key_exists($tagname, $output)) {
      $output[$tagname]["#attached"]["drupal_add_html_head"][0][0]["#value"] = $value;
    }
    else {
      $output[$tagname] = [
        '#attached' => [
          'drupal_add_html_head' => [
            [
              [
                '#theme' => 'metatag_property',
                '#tag' => 'meta',
                '#id' => "{$tagname}_0",
                '#name' => $tagname,
                '#value' => $value,
                '#weight' => 100,
              ],
              "{$tagname}_0",
            ]
          ]
        ]
      ];
    }
  }
}