Add "selected" class to custom taxonomy dropdown search

Question

I found the following function to add a custom taxonomy dropdown to a search form. It works fine for searching, but it does not add the "selected" class to the searched-for term. Here is my code for the taxonomy named grades:

function get_terms_grades_dropdown($taxonomies, $args)
    {
        global $search_values;

        $myterms = get_terms($taxonomies, $args);
        $output = "";
        foreach ($myterms as $term) {
            $root_url = get_bloginfo('url');
            $term_taxonomy = $term->taxonomy;
            $term_slug = $term->slug;
            $term_name = $term->name;
            $value = $term->term_id;
            if ($search_values['grades'] == $term->slug) {
                $selected = "selected='selected'";
            } else {
                $selected = '';
            }
            $output .= "<option value='" . $value . "' " . $selected . ">" . $term_name . "</option>";
        }

        return $output;
    }

Then I use the function like this:

<select name="grade" id="grade_search">
    <option value="" selected="selected">Grade Level</option>
    <?php
    $taxonomies = array('grades');
    $args = array('orderby'=>'count','hide_empty'=>true);
    echo get_terms_grades_dropdown($taxonomies, $args);
    ?>
</select>

The issue is with this line:

if ($search_values['grades'] == $term->slug) {

I need to get $search_values['grades'] to equal the searched-for term.

Thank you!

Answer 1

$seach_values can be changed whenever the site redirect, be sure that $search_values still keeps the input values from your search form.

To be sure I suggest use GET or POST to pass the values from form. So, your comparing statement should be

$_GET['grades'] == $term->slug

Here I suppose your search form use method="GET"