Grav\Plugin\AdminPlugin::onOutputGenerated PHP Method

    public function onOutputGenerated()
    {
        // Clear flash objects for previously uploaded files
        // whenever the user switches page / reloads
        // ignoring any JSON / extension call
        if (is_null($this->uri->extension()) && $this->admin->task !== 'save') {
            // Discard any previously uploaded files session.
            // and if there were any uploaded file, remove them from the filesystem
            if ($flash = $this->session->getFlashObject('files-upload')) {
                $flash = new \RecursiveIteratorIterator(new \RecursiveArrayIterator($flash));
                foreach ($flash as $key => $value) {
                    if ($key !== 'tmp_name') {
                        continue;
                    }
                    @unlink($value);
                }
            }
        }
    }