Form Fields in Plugin

function JobApplication()
 {
  $this->EE =& get_instance();
  $this->data = $this->EE->TMPL->tagdata; 
  
  if ($this->EE->TMPL->fetch_param('id') && $this->EE->TMPL->fetch_param('siteid'))
  {
   $this->_id = $this->EE->TMPL->fetch_param('id');
   $this->_siteid = $this->EE->TMPL->fetch_param('siteid');
   $this->_memberid = $this->EE->session->userdata['member_id'];
   $this->_source = $this->EE->TMPL->fetch_param('source');
   $this->_firstname = $_POST['firstname'];
   $this->_lastname = $_POST['lastname'];
          $this->_email = $_POST['email'];
   $this->_track_job_application();
  
  }
  else
  {
   //return $this->return_data; 
  }  
 }