Uncaught RuntimeException: Callable does not exist - php

Question

I am trying a simple Slim application as shown below.
index.php
<?php
use Slim\Factory\AppFactory;
require './vendor/autoload.php';
$app = AppFactory::create();
$app->get('/', [TestController::class, 'showBlank']);
$app->run();
And below is the TestController.php.
<?php
use \Psr\Container\ContainerInterface;
use Psr\Http\Message\ServerRequestInterface;
use Slim\Http\Interfaces\ResponseInterface;
class TestController
{
protected $c;
public function __construct(ContainerInterface $c)
{
$this->c = $c;
}
public function showBlank(ServerRequestInterface $request, ResponseInterface $response, array $args): ResponseInterface
{
return $response;
}
}
Below is the project structure.
C:\laragon\www\chum>ls
composer.json composer.lock index.php TestController.php vendor
Since I am trying slim for first time, I am keep the example to very minimal and so the composer.json file.
{
"require": {
"slim/slim": "^4.11",
"slim/psr7": "^1.6",
"slim/twig-view": "^3.3",
"slim/http": "^1.3"
}
}
Given these, I am getting the below exceptio when I try to access the root page(\).
Fatal error: Uncaught RuntimeException: Callable TestController::showBlank() does not exist in C:\laragon\www\chum\vendor\slim\slim\Slim\CallableResolver.php:138
Stack trace:
#0 C:\laragon\www\chum\vendor\slim\slim\Slim\CallableResolver.php(90): Slim\CallableResolver->resolveSlimNotation('TestController:...')
#1 C:\laragon\www\chum\vendor\slim\slim\Slim\CallableResolver.php(63): Slim\CallableResolver->resolveByPredicate('TestController:...', Array, 'handle')
#2 C:\laragon\www\chum\vendor\slim\slim\Slim\Routing\Route.php(340): Slim\CallableResolver->resolveRoute(Array)
#3 C:\laragon\www\chum\vendor\slim\slim\Slim\MiddlewareDispatcher.php(65): Slim\Routing\Route->handle(Object(Slim\Http\ServerRequest))
#4 C:\laragon\www\chum\vendor\slim\slim\Slim\MiddlewareDispatcher.php(65): Slim\MiddlewareDispatcher->handle(Object(Slim\Http\ServerRequest))
#5 C:\laragon\www\chum\vendor\slim\slim\Slim\Routing\Route.php(315): Slim\MiddlewareDispatcher->handle(Object(Slim\Http\ServerRequest))
#6 C:\laragon\www\chum\vendor\slim\slim\Slim\Routing\RouteRunner.php(68): Slim\Routing\Route->run(Object(Slim\Http\ServerRequest))
#7 C:\laragon\www\chum\vendor\slim\slim\Slim\MiddlewareDispatcher.php(65): Slim\Routing\RouteRunner->handle(Object(Slim\Http\ServerRequest))
#8 C:\laragon\www\chum\vendor\slim\slim\Slim\App.php(199): Slim\MiddlewareDispatcher->handle(Object(Slim\Http\ServerRequest))
#9 C:\laragon\www\chum\vendor\slim\slim\Slim\App.php(183): Slim\App->handle(Object(Slim\Http\ServerRequest))
#10 C:\laragon\www\chum\index.php(56): Slim\App->run() #11 {main} thrown in C:\laragon\www\chum\vendor\slim\slim\Slim\CallableResolver.php on line 138

Answer 1

Thanks Alvaro for the great tips in comments, I was able to solve it with some further help from Google based on that.
I was under assumption flat project structure does not need namespaces to be configured. But I was wrong.
I did the below updates to composer.json file and ran composer dump-autoload -o.
"autoload": {
"psr-4": {
"App\\": ""
}
},