--- /dev/null
+<?php
+
+namespace Drupal\{{ machine_name }}\Theme;
+
+use Drupal\Core\Routing\RouteMatchInterface;
+use Drupal\Core\Theme\ThemeNegotiatorInterface;
+use Symfony\Component\HttpFoundation\RequestStack;
+
+/**
+ * Defines a theme negotiator that deals with the active theme on example page.
+ */
+class {{ class }} implements ThemeNegotiatorInterface {
+
+ /**
+ * The request stack.
+ *
+ * @var \Symfony\Component\HttpFoundation\RequestStack
+ */
+ protected $requestStack;
+
+ /**
+ * Constructs a new {{ class }}.
+ *
+ * @param \Symfony\Component\HttpFoundation\RequestStack $request_stack
+ * The request stack used to retrieve the current request.
+ */
+ public function __construct(RequestStack $request_stack) {
+ $this->requestStack = $request_stack;
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function applies(RouteMatchInterface $route_match) {
+ return $route_match->getRouteName() == '{{ machine_name }}.example';
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function determineActiveTheme(RouteMatchInterface $route_match) {
+ // Allow users to pass theme name through 'theme' query parameter.
+ $theme = $this->requestStack->getCurrentRequest()->query->get('theme');
+ if (is_string($theme)) {
+ return $theme;
+ }
+ }
+
+}