为什么CodeIgniter中的flashdata并不总是有效，而userdata总能工作？

Question

I have one code block for assigning some values to flashdata in report controller and another block for accessing flashdata in export_data controller.

Report Controller:

if ($this->input->get_post('date_frm')) {
              $conditions[] = 'appointment_date >= "'.trim($this->input->get_post('date_frm', TRUE)).'"';
            }

            if ($this->input->get_post('date_to')) {
              $conditions[] = 'appointment_date <= "'.trim($this->input->get_post('date_to', TRUE)).'"';
            }

            $conditions = $this->search_model->searchterm_handler($conditions);

            $this->session->set_flashdata('ext_data', $conditions);

And in Export_data Controller:

$myVar = $this->session->flashdata('ext_data');
    $this->session->keep_flashdata('ext_data');

It does not always work, but when I use userdata rather than flashdata it is working fine. Why?

Answer 1

OP: when I use userdata rather than flashdata it is working fine

Data set with flashdata() is only saved for a one-time request, then cleared out:

Documentation: CodeIgniter supports “flashdata”, or session data that will only be available for the next request, and is then automatically cleared.

...and keep_flashdata() only saves the data for one additional request after the first:

Documentation: If you find that you need to preserve a flashdata variable through an additional request, you can do so using the keep_flashdata() method.

---

However, userdata() is always available until the session is destroyed.

See: What is Session Data?

---

I think you should read the full documentation: Session Library