表单无法添加到wordpress插件子菜单页面

Ok so I was able to create the sub menu page but I'm unable to get the form to be displayed on the sub menu page? What would be the problem? Here is the code I'm using below. Thanks!

    $submenuone = add_submenu_page(UR_FILE, 'Add New User', __('Add New User', UR_NAME), 'ur_create_form', 'ur_create_user', array($this, 'render_ur_user'));

    function render_ur_user() {
                if (!current_user_can('ur_create_user')) {
                    wp_die(__('Access denied.', UR_NAME));
                }
                $add_user .= $this->add_wrap(__('Add USER', UR_NAME), "<br>"--"</br>);

                $add_user .= "<form id='ur-user-form'>
";
                $add_user .= "<p><input type='text' id='user-name' name='user-name' value='' /> ";

                $add_user .= $this->add_wrap(__('Add User', UR_NAME), "<button class='add btn-cone'>", "</button></p>");
                $add_user .= "</form>
";
            }

Now for the query

function db_insert_new_user($input) {
            global $wpdb;

            $result = $wpdb->insert($wpdb->prefix . UR_USERTBL,
                                    array('name'    => $input->name,
                                          'surname' => $input->surname
                                    ),
                                    array('%s'),
                                    array('%s')
                                    );
            if ($this->return_result($result)){
                $input->user_id = $wpdb->insert_id;
                $this->renderuser($input);
            }
        }

function renderuser($input){
            $output = array(
                'user_id'           => $input->user_id,
                'name'  => $input->name,
                'surname' => $input->surname
            );
            $this->render_json($output);
        }

Can anyone tell me, why isn't my form being displayed on the sub menu page? (ALSO) Once I do get it working, how to do I submit these values to the database(mySql)? Thanks!

The function add_submenu_page calls needs to output something. The form HTML is set in the variable $add_user but isn't being displayed. Change the last few lines to

            $add_user .= "</form>
";
            echo($add_user);
        }