遇到PHP错误严重性：通知消息：未定义的索引：问题

Question

<?php
    if ( ! defined('BASEPATH')) exit('No direct script access allowed');
    class checklist extends CI_Controller 
    {
        function __construct()
        {
            parent::__construct();
            $this->load->helper('url');
            $this->load->helper('form');
            $this->load->model('checklist_model');
        }
        public function index()
        {
            $data['check_list'] = $this->checklist_model->get_all_details();
            $this->load->view('show_checklist', $data);
        }
        public function form_dropdown() 
        {
            $this->load->view('insert_checklist');
        }
        public function data_submitted()
        {

            $data = array('dropdown_single' => $this->input->post('Technology'));
            $this->load->model('checklist_model');
            $this->checklist_model->insert_in_db($data);
            $this->load->model("checklist_model");
            $result = $this->checklist_model->read_from_db($data);
            $data['result'] = $result[0];
            $this->load->view('insert_checklist', $data);
        }   
        public function add_form()
        {
            $this->load->view('insert_checklist');
        }
        public function edit()
        {
            $id = $this->uri->segment(3);
             $data['details'] = $this->checklist_model->getById($id);
            $this->load->view('edit', $data);
        }
        public function delete($id)
        {
            $this->checklist_model->delete_a_detail($id);
            $this->index();
        }
        public function insert_new_details()
        {
            $udata['technology_name'] = $this->input->post('technology_name');
            $udata['questions'] = $this->input->post('questions');
            $udata['status'] = $this->input->post('status');
            $udata['comments'] = $this->input->post('comments');
            $res = $this->checklist_model->insert_details_to_db($udata);
            if($res)
            {
                header('location:'.base_url()."/index.php/checklist/".$this->index());
            }
        }
        public function update()
        {
            $mdata['technology_name']=$_POST['technology_name'];
            $mdata['questions']=$_POST['questions'];
            $mdata['status']=$_POST['status'];
            $mdata['comments']=$_POST['comments'];
            $res=$this->checklist_model->update_info($mdata, $_POST['id']);
            if($res)
            {
                header('location:'.base_url()."/index.php/checklist/".$this->index());
            }
        }
    }
?>