Clear cache after changing wwwroot

lib.php

@@ -0,0 +1,37 @@
+<?php
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+/**
+ * Functions for the QR code block.
+ *
+ * @package block_qrcode
+ * @copyright 2026 L. Herfeldt
+ * @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
+ */
+
+/**
+ * Clears cached QR code images when relevant global settings are changed.
+ *
+ * This is used after changing the custom wwwroot, because existing cached
+ * QR image files may still contain the old URL.
+ */
+function block_qrcode_clear_cache(): void {
+    $cachedir = make_localcache_directory('block_qrcode', false);
+
+    if ($cachedir !== false && is_dir($cachedir)) {
+        remove_dir($cachedir, true);
+    }
+}

settings.php

@@ -23,15 +23,20 @@
  */
 
 defined('MOODLE_INTERNAL') || die;
+require_once($CFG->dirroot . '/blocks/qrcode/lib.php');
 
 if ($ADMIN->fulltree) {
-    $settings->add(new admin_setting_configtext(
+    $setting = new admin_setting_configtext(
         'block_qrcode/custom_wwwroot',
         new lang_string('customwwwroot', 'block_qrcode'),
         new lang_string('customwwwroot_desc', 'block_qrcode', $CFG->wwwroot),
         '',
-        PARAM_URL,
-    ));
+        PARAM_URL
+    );
+
+    $setting->set_updatedcallback('block_qrcode_clear_cache');
+
+    $settings->add($setting);
 
     $settings->add(new admin_setting_configcheckbox(
         'block_qrcode/use_logo',