Isset with multi select dropdown and bootstrap - php

Question

I have a wordpress site with a search form that searches for posts based on the form field selections, for custom fields etc. It works fine, however on the search results page I have an exact copy of the form except that I am trying to preset the form selections based on the search query/url string.
I am using a regular select dropdown and I have set it to "multiple" so that it can use bootstraps multiselect with the checkboxes. I've asked a similar question HERE but that was for checkboxes and even though the bootstrap multiselect uses checkboxes, I still have to work with the select dropdown first.
So after trying several things, I've come close but have ran into several problems. In the code below I made notes to further explain exactly what I mean.
<select name="property_type[]" id="pt-multi" class="form-control multi-select2" multiple="multiple">
<?php
$terms = get_terms( "property-type", array( 'hide_empty' => 0 ) );
$count = count($terms);
if ( $count > 0 ){
echo "<option value='Any'>All</option>";
foreach ( $terms as $term ) {
if (isset($_GET['property_type'])) {
foreach ($_GET['property_type'] as $proptypes) {
// FIRST EXAMPLE
$selected .= ($proptypes === $term->slug) ? "selected" : ""; // shows first correct selected value but also selects everything after it up until the second correct value, which it doesn't select.
//$selected = ($proptypes === $term->slug) ? "selected" : ""; // shows only last correct selected value
//if ($proptypes === $term->slug) { $selected = 'selected'; } // shows first correct selected value then selects every value after, even if it wasn't selected
// SECOND EXAMPLE
//$selected .= ($proptypes === $term->slug) ? "selected" : ""; // shows first correct selected value then selects every value after, even if it wasn't selected
//$selected = ($proptypes === $term->slug) ? "selected" : ""; // shows only last correct selected value
//if ($proptypes === $term->slug) { $selected = 'selected'; } // shows first correct selected value then selects every value after, even if it wasn't selected
}
}
echo "<option value='" . $term->slug . "' " . $selected . ">" . $term->name . "</option>"; // FIRST EXAMPLE
//echo "<option value='" . $term->slug . "' " . ($selected?' selected':'') . ">" . $term->name . "</option>"; // SECOND EXMAPLE
}
}
?>
</select>

Answer 1

Create and array and use in_array() to check.
<select name="property_type[]" id="pt-multi" class="form-control multi-select2" multiple="multiple">
<?php
$terms = get_terms("property-type", array('hide_empty' => 0));
$count = count($terms);
// Setup an array of $proptypes
$proptypes = array();
if (isset($_GET['property_type'])) {
foreach ($_GET['property_type'] as $proptype) {
$proptypes[] = $proptype;
}
}
if ($count > 0) {
echo "<option value='Any'>All</option>";
foreach ($terms as $term) {
$selected = (in_array($term->slug, $proptypes)) ? 'selected' : '';
echo "<option value='" . $term->slug . "' " . $selected . ">" . $term->name . "</option>";
}
}
?>
</select>