数据未在会话代码点火器中设置

//uploading product movie or image?
        if($this->input->post('upload_360') == "Upload") {
            $config['upload_path'] = './media/images/products/360s';
            $config['allowed_types'] = 'swf';
            $this->load->library('upload', $config);
            $this->upload->initialize($config);
            if (!$this->upload->do_upload('film')) {
                $this->data['product_error'] = $this->upload->display_errors();
                $this->template->build('/admin/products/create', $this->data);
            } else {
                $this->data['data_360'] = $this->upload->data();
                $this->session->set_userdata(array('360_film' => $this->data['data_360']));
                $this->template->build('/admin/products/create', $this->data);
            }
            $this->session->set_userdata(array('advantages' => $this->input->post('product_advantages')));
            $this->data['session_advantages'] = $this->session->userdata('advantages');
        }
        //upload the product image, if successful the user will be
        //notified if the image is too high or wide, and will be offered,
        //the chance to crop the image. All cropping takes place in the media
        //controller.
        if($this->input->post('product_image') == "Upload") {
            $config['upload_path'] = './media/images/products/';
            $config['allowed_types'] = 'gif|jpg|jpeg|png';
            $this->load->library('upload', $config);
            $this->upload->initialize($config);
            if (!$this->upload->do_upload('image_upload')) {
                //die("!");
                $this->data['image_error'] = $this->upload->display_errors();
                $this->template->build('/admin/products/create', $this->data);
            } else {
                $this->data['image_data'] = $this->upload->data();
                $this->session->set_userdata(array('image' => $this->data['image_data']));
                $this->data['session_image'] = $this->session->userdata('image');
                $this->template->build('/admin/products/create', $this->data);
            }
            $this->session->set_userdata(array('advantages' => $this->input->post('product_advantages')));
            $this->data['session_advantages'] = $this->session->userdata('advantages');
        }
        if($this->input->post('screenshot_upload') == "Upload") {
            $config['upload_path'] = './media/images/products/360s/screenshots/';
            $config['allowed_types'] = 'gif|jpg|jpeg|png';
            $this->load->library('upload', $config);
            $this->upload->initialize($config);
            if (!$this->upload->do_upload('screenshot')) {
                //die("!");
                $this->data['screenshot_error'] = $this->upload->display_errors();
                $this->template->build('/admin/products/create', $this->data);
            } else {
                $this->data['screenshot_data'] = $this->upload->data();
                $this->session->set_userdata(array('screenshot' => $this->data['screenshot_data']));
                $this->data['session_screenshot'] = $this->session->userdata('screenshot');
                $this->template->build('/admin/products/create', $this->data);
            }
            $this->session->set_userdata(array('advantages' => $this->input->post('product_advantages')));
            $this->data['session_advantages'] = $this->session->userdata('advantages');
        }

在我的表单上，我让用户选择一个文件，然后单击上传按钮取决于单击哪个按钮，上传文件并将上传数据保存在会话中。

然后会话用于从中获取数据以保存到数据库，upload_360会话有效，product_image会话工作正常，但screenshot_upload会话仅在使用 if 语句(代码中的第 3 条(时才有数据，如果我尝试在代码之外访问它，那么会话的那部分是空的？

这有什么原因吗？