Accessing "$request" and "validate" from another class

I have a subfolder inside controller app/Controller/AppManager. Inside it there is a class named "MediaManager.php" which is extended with use CodeIgniter\Controller;.

PHP Code:

<?php

namespace App\Controllers\AppManager;
use CodeIgniter\Controller;

class MediaManager extends Controller
{
    public function uploadFile(){
        $file = $this->request->getFile('file');
        $fileRule = ['file' => 'uploaded[file]|max_size[file,20480]'];

        if( ! $this->validate($fileRule) ) $ret = ['e', 'FAILED', $this->validator->listErrors()];
        ...
        ...
        ...
    }
} 


Now the problem is, when ever I am going to upload a file, these errors are showing:

• Call to a member function getFile() on null
  
• Argument 1 passed to CodeIgniter\Validation\Validation::withRequest() must implement interface CodeIgniter\HTTP\RequestInterface, null given
  

How can I access the Request and Validation property in this class?

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