Contao\BackendFile::run PHP Method

    public function run()
    {
        /** @var SessionInterface $objSession */
        $objSession = \System::getContainer()->get('session');
        /** @var BackendTemplate|object $objTemplate */
        $objTemplate = new \BackendTemplate('be_picker');
        $objTemplate->main = '';
        // Ajax request
        if ($_POST && \Environment::get('isAjaxRequest')) {
            $this->objAjax = new \Ajax(\Input::post('action'));
            $this->objAjax->executePreActions();
        }
        $strTable = \Input::get('table');
        $strField = \Input::get('field');
        // Define the current ID
        define('CURRENT_ID', \Input::get('table') ? $objSession->get('CURRENT_ID') : \Input::get('id'));
        $this->loadDataContainer($strTable);
        $strDriver = 'DC_' . $GLOBALS['TL_DCA'][$strTable]['config']['dataContainer'];
        $objDca = new $strDriver($strTable);
        $objDca->field = $strField;
        // Set the active record
        if ($this->Database->tableExists($strTable)) {
            /** @var Model $strModel */
            $strModel = \Model::getClassFromTable($strTable);
            if (class_exists($strModel)) {
                $objModel = $strModel::findByPk(\Input::get('id'));
                if ($objModel !== null) {
                    $objDca->activeRecord = $objModel;
                }
            }
        }
        // AJAX request
        if ($_POST && \Environment::get('isAjaxRequest')) {
            $this->objAjax->executePostActions($objDca);
        }
        $objSession->set('filePickerRef', \Environment::get('request'));
        $arrValues = array_filter(explode(',', \Input::get('value')));
        // Convert UUIDs to binary
        foreach ($arrValues as $k => $v) {
            // Can be a UUID or a path
            if (\Validator::isStringUuid($v)) {
                $arrValues[$k] = \StringUtil::uuidToBin($v);
            }
        }
        // Call the load_callback
        if (is_array($GLOBALS['TL_DCA'][$strTable]['fields'][$strField]['load_callback'])) {
            foreach ($GLOBALS['TL_DCA'][$strTable]['fields'][$strField]['load_callback'] as $callback) {
                if (is_array($callback)) {
                    $this->import($callback[0]);
                    $arrValues = $this->{$callback[0]}->{$callback[1]}($arrValues, $objDca);
                } elseif (is_callable($callback)) {
                    $arrValues = $callback($arrValues, $objDca);
                }
            }
        }
        /** @var FileSelector $strClass */
        $strClass = $GLOBALS['BE_FFL']['fileSelector'];
        /** @var FileSelector $objFileTree */
        $objFileTree = new $strClass($strClass::getAttributesFromDca($GLOBALS['TL_DCA'][$strTable]['fields'][$strField], $strField, $arrValues, $strField, $strTable, $objDca));
        /** @var AttributeBagInterface $objSessionBag */
        $objSessionBag = $objSession->getBag('contao_backend');
        $objTemplate->main = $objFileTree->generate();
        $objTemplate->theme = \Backend::getTheme();
        $objTemplate->base = \Environment::get('base');
        $objTemplate->language = $GLOBALS['TL_LANGUAGE'];
        $objTemplate->title = \StringUtil::specialchars($GLOBALS['TL_LANG']['MSC']['filepicker']);
        $objTemplate->charset = \Config::get('characterSet');
        $objTemplate->addSearch = true;
        $objTemplate->search = $GLOBALS['TL_LANG']['MSC']['search'];
        $objTemplate->searchExclude = $GLOBALS['TL_LANG']['MSC']['searchExclude'];
        $objTemplate->action = ampersand(\Environment::get('request'));
        $objTemplate->value = $objSessionBag->get('file_selector_search');
        $objTemplate->breadcrumb = $GLOBALS['TL_DCA']['tl_files']['list']['sorting']['breadcrumb'];
        if ($this->User->hasAccess('files', 'modules')) {
            $objTemplate->manager = $GLOBALS['TL_LANG']['MSC']['fileManager'];
            $objTemplate->managerHref = 'contao/main.php?do=files&popup=1';
        }
        if (\Input::get('switch') && $this->User->hasAccess('page', 'modules')) {
            $objTemplate->switch = $GLOBALS['TL_LANG']['MSC']['pagePicker'];
            $objTemplate->switchHref = str_replace('contao/file?', 'contao/page?', ampersand(\Environment::get('request')));
        }
        return $objTemplate->getResponse();
    }

 /**
  * Renders the file picker.
  *
  * @return Response
  *
  * @Route("/file", name="contao_backend_file")
  */
 public function fileAction()
 {
     $this->container->get('contao.framework')->initialize();
     $controller = new BackendFile();
     return $controller->run();
 }