how to get value of wp_dropdown_categories

We can get the categories via get_categories() function (which will get the same categories as wp_dropdown_categories() function), but as array and without the markup.

As the value is returned as array, we can loop through the categories and generate the HTML ourself.

Usually, we would aim for a structure like this:

<select name="categories">
  <option value="1">Category 1</option>
  <option value="2">Category 2</option>
  <option value="3">Category 3</option>
</select>

So we’re going to generate the structure from above via PHP by looping through the $categories array:

echo '<select name="categories">';

  // Get categories as array
  $categories = get_categories( $args );
  foreach ( $categories as $category ) :

    echo '<option value="' . $category->term_id . '">' . $category->name . '</option>';

  endforeach;

echo '</select>';

Feel free to modify the function via the $args parameters (see Codex for reference).

Now we’ll just need to add the selected attribute within the <option>, so we’re going to add this via a short if statement to compare the current $category->term_id and the one saved in the database $stored_category_id:

$stored_category_id = 10; // This is the value from the database
$selected = ( $stored_category_id == $category->term_id  ) ? 'selected' : '';

And that’s it! Your complete snippet (maybe with a default option at the beginning) should now look something like this:

echo '<select name="categories">';
  // Add custom option as default
  echo '<option>' . __('No Category', 'text-domain') . '</option>';

  // Get categories as array
  $categories = get_categories( $args );
  foreach ( $categories as $category ) :

    // Check if current term ID is equal to term ID stored in database
    $selected = ( $stored_category_id ==  $category->term_id  ) ? 'selected' : '';

    echo '<option value="' . $category->term_id . '" ' . $selected . '>' . $category->name . '</option>';

  endforeach;

echo '</select>';

Good luck! 🙂