Joomla 4 - Invalid controller class:display

Question

I'm building a simple component in Joomla 4, and after reading through some tutorials I feel like I've got it right - but I'm getting this error that I can't explain in the admin view

An error has occurred.
0 Invalid controller class: display

With logging enabled, this is what I see in everything.php:

#Fields: datetime   priority clientip   category    message
2022-11-18T17:52:12+00:00   CRITICAL ::1    error   Uncaught Throwable of type InvalidArgumentException thrown with message "Invalid controller class: display". Stack trace: #0 [ROOT]\libraries\src\Dispatcher\ComponentDispatcher.php(142): Joomla\CMS\Dispatcher\ComponentDispatcher->getController('display', 'Administrator', Array)
#1 [ROOT]\libraries\src\Component\ComponentHelper.php(355): Joomla\CMS\Dispatcher\ComponentDispatcher->dispatch()
#2 [ROOT]\libraries\src\Application\AdministratorApplication.php(143): Joomla\CMS\Component\ComponentHelper::renderComponent('com_testcomponent')
#3 [ROOT]\libraries\src\Application\AdministratorApplication.php(186): Joomla\CMS\Application\AdministratorApplication->dispatch()
#4 [ROOT]\libraries\src\Application\CMSApplication.php(294): Joomla\CMS\Application\AdministratorApplication->doExecute()
#5 [ROOT]\administrator\includes\app.php(61): Joomla\CMS\Application\CMSApplication->execute()
#6 [ROOT]\administrator\index.php(32): require_once('F:\\xampp\\htdocs...')
#7 {main}

My DisplayController.php file is at:

joomla\administrator\components\com_testcomponent\src\Controller\DisplayController.php

<?php

namespace Joomla\Component\Testcomponent\Administrator\Controller;

use Joomla\CMS\MVC\Controller\BaseController;

\defined('_JEXEC') or die;

class DisplayController extends BaseController
{
    protected $default_view = 'orders';
}

Answer 1

I was having the same problem! I struggled a whole day with why this error comes up; even a namespace path like

<namespace path="src/">TestComp\Component\Testcomponent</namespace>

has been given in the manifest file.

After reverse engineering Joomla's 'hello world' example @ https://docs.joomla.org/J4.x:Developing_an_MVC_Component/Developing_a_Basic_Component#helloworld.xml, I found a very interesting part which seems to be responsible for this error in my case.

In the manifest file, there is the tag field <name></name>. Usually, I thought here we could free define a name for our component, because there is not much info in the documentation. In the past, very often the raw name of the component has been typed here, eg <name>com_helloworld</name>. In the documentation from Joomla, you see that normal names can also be given. In this example it is <name>Hello World</name>.

And here comes the important point, if the name does not match the component name then you will encounter the error: 'Invalid Controller class: display'. Debugging showed me, that the responsible controller file will not be loaded. In my example I developed a component with the name 'com_testdev'. In the field of the manifest I typed <name>Test Development</name>. With this name the mentioned error comes up. Changing the the field to <name>Test Dev</name> resolved the problem!

Answer 2

I added a namespace to my manifest file, and the issue is resolved.

<namespace path="src/">TestComp\Component\Testcomponent</namespace>

Answer 3

For me after upgrading to Joomla 4.3 I got this error on random Joomla pages. I found that I had many menu items that were for whatever reason pointing to the wrong component (in my case com_template mostly and one pointing to nothing with id 0). To see if you have any dangling component menu items query your db with the following:

SELECT * FROM `#__menu` WHERE 1 AND link LIKE '%=com_content%' AND type = 'component' AND component_id != (SELECT extension_id FROM #__extensions WHERE name = 'com_content');

Export the previous as a backup if needed to have a reference of which ones are off. To set them right and get rid of the error try executing in your db:

UPDATE `#__menu` SET `component_id` = (SELECT extension_id FROM #__extensions WHERE name = 'com_content' LIMIT 1) WHERE 1 AND link LIKE '%=com_content%' AND type = 'component' AND component_id != (SELECT extension_id FROM #__extensions WHERE name = 'com_content' LIMIT 1);