Uploading multiple file using codeigniter - codeigniter

Question

I got a problem with multiple upload file using codeigniter. I've tried many method before but still no success.
Here is my code.
View
<?php echo form_open_multipart('staff/upload_files', array('id' => 'form_checkbox')); ?>
Inside table:
<tr>
<th width="20%">Select File :</th>
<td>
<input type="file" name="userfile[]" value="" /> <span class="green">[Max File Upload: 2MB]</span><br>
<input type="file" name="userfile[]" value="" /> <span class="green">[Max File Upload: 2MB]</span><br>
<input type="file" name="userfile[]" value="" /> <span class="green">[Max File Upload: 2MB]</span>
</td>
</tr>
Controller
function upload_files() {
$data['studentid'] = $studentid;
if ($this->input->post('submit')) {
$config['upload_path'] = './upload/announcement/collegecode/';
$config['allowed_types'] = 'jpg|png';
$config['max_size'] = '2048';
$config['max_width'] = '0';
$config['max_height'] = '0';
$config['overwrite'] = FALSE;
$this->load->library('upload', $config);
if (!$this->upload->do_upload()) {
$this->session->set_flashdata('msg', 'error: ' . $this->upload->display_errors());
} else {
$this->session->set_flashdata('msg', 'success:Successfully Upload Student Photo');
}
}
$this->template->load('template', 'staff/announcement', $data);
}
I've also tried this method, but no file was uploaded.
$config['upload_path'] = './upload/announcement/collegecode/';
$path=$config['upload_path'];
$config['allowed_types'] = 'gif|jpg|jpeg|png';
$config['max_size'] = '2048';
$config['max_width'] = '1920';
$config['max_height'] = '1280';
$this->load->library('upload');
foreach ($_FILES as $key => $value)
{
if (!empty($key['userfile']))
{
$this->upload->initialize($config);
if (!$this->upload->do_upload($key))
{
$errors = $this->upload->display_errors();
flashMsg($errors);
}
else
{
// Code After Files Upload Success GOES HERE
}
}
}