Backward compatibility with Magento without VarDumper, thanks to @dudzio12

Author: vpietri

Helper/Data.php

@@ -93,6 +93,11 @@ public function getCacheFrontendPool()
 
     public function getQdbConfig($key, $scopeType = ScopeConfigInterface::SCOPE_TYPE_DEFAULT, $scopeCode = null)
     {
+        // Backward compatibility
+        if($key=='handle_vardumper' && !class_exists(\Symfony\Component\VarDumper\VarDumper::class)) {
+            return false;
+        }
+
         return $this->getConfig('dev/quickdevbar/'.$key, $scopeType, $scopeCode);
     }
 

Plugin/Framework/App/FrontController.php

@@ -6,10 +6,6 @@
 use ADM\QuickDevBar\Helper\Register;
 use ADM\QuickDevBar\Service\Dumper;
 use Magento\Framework\App\RequestInterface;
-use Symfony\Component\VarDumper\Dumper\HtmlDumper;
-use Symfony\Component\VarDumper\VarDumper;
-use Symfony\Component\VarDumper\Cloner\VarCloner;
-
 
 class FrontController
 {
@@ -63,7 +59,7 @@ public function beforeDispatch(\Magento\Framework\App\FrontControllerInterface $
             if($this->request->isAjax() && $enabledHandler<2) {
                 return;
             }
-            //$prevHandler = VarDumper::setHandler($this->dumperHandler(...));
+            $prevHandler = \Symfony\Component\VarDumper\VarDumper::setHandler($this->dumperHandler(...));
         }
     }
 
@@ -73,8 +69,8 @@ public function beforeDispatch(\Magento\Framework\App\FrontControllerInterface $
      */
     protected function dumperHandler($var)
     {
-        $cloner = new VarCloner();
-        $dumper = new HtmlDumper();
+        $cloner = new \Symfony\Component\VarDumper\Cloner\VarCloner();
+        $dumper = new \Symfony\Component\VarDumper\Dumper\HtmlDumper();
 
         $dumper->setTheme('dark');
         $dumpBt = debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS)[2];

view/base/templates/tab/dumper.phtml

@@ -1,6 +1,11 @@
 <?php
 /** @var  $block \ADM\QuickDevBar\Block\Tab\Panel */
 ?>
+<?php if(!$block->getQdbConfig('handle_vardumper')):?>
+<p>You need to activate admin configuration and having VarDumper Component installed, see <a href="https://github.com/symfony/var-dumper">github.com/symfony/var-dumper</a></p>
+<?php endif; ?>
+
+
 
 <?php if(!$block->getDumps()): ?>
     <div class="qdb-dump"></div>