php - Combobox Validation in Codeigniter -

i have view

echo "<td>";     $combokategori[] =  '';     $attribute = "id='kategori' style='width:8.5em' onchange='retrieve();'";     echo form_dropdown('kategori', $combokategori, '', $attribute);     echo "</td>";     echo "<td>";     $inputdeskripsi = array(         'name'      => 'deskripsi',         'id'        => 'deskripsi',         'onkeyup'   => 'retrieve()'     );     echo form_input($inputdeskripsi); echo "</td>"; 

and validation on controller

$this->load->library('form_validation'); $this->form_validation->set_rules('kategori', 'kategori', 'required'); $this->form_validation->set_rules('deskripsi', 'deskripsi', 'required'); 

after submit empty form, validator detect one. , show error. combobox not validate.

the deskripsi field required.