如何在codeigniter中正确设置flash_message？

I have a problem like this.I am using Code igniter to build a website.I want to pass a flash message when redirecting from a controller.For that I have make this code.

$data['message']=$this->session->set_flashdata('item', array('message' => 'Record created successfully','class' => 'success'));
var_dump($data['message']);
return;
redirect('question/index',$data);

Then i used var_dump to make sure that everything is work fine.but it print null.What is the issue of this.How can I fix this?

Full code for flash message :

Controller :

      $query = $this->db->insert(table_name,$array_data);

      if($query){
        $this->session->set_flashdata('success', 'Sucessful added Multiple Image');
        redirect($this->redirect);
      }
      else{
        $this->session->set_flashdata('error', 'Something is wrong. Error!!');
        redirect($this->redirect);
      }

alert.php(view file)

<?php if ($this->session->flashdata('success')) { ?>

        <div class="alert alert-success">
          <a href="#" class="close" data-dismiss="alert" aria-label="close">×</a>
            <strong><?php echo $this->session->flashdata('success'); ?></strong>
        </div>

<?php } ?>

<?php if ($this->session->flashdata('error')) { ?>

        <div class="alert alert-danger">
            <a href="#" class="close" data-dismiss="alert" aria-label="close">×</a>
            <strong><?php echo $this->session->flashdata('error'); ?></strong>
        </div>

<?php } ?>

List.php(view file)

<?php
    $this->load->view('alert');
 ?>

set_flashdata returns void, so it is reasonable that var_dump shows nothing.

According to its manual:

CodeIgniter supports "flashdata", or session data that will only be available for the next server request, and are then automatically cleared.

Which obviously means that you just need to do a new server request. A redirect, refresh, link or just something that redirects user to the next request.

Setting Flashdata in your Controller Method

$this->session->set_flashdata('success', "Password Changed");

Now Print Message in your view like this.

$data['message'] = $this->session->flashdata('success');