PHP impossible d'obtenir l'id dans le URL et afficher sa

Bonjour,

Voila je rencontre un petit problème avec mon code.

je suis en cours de dévelloppement d'un mini site en Php,

je cherche a obtenir l'id dans le URL du navligateur atravers la requete $_Get['id']

ceci es le fichier DB 
<?php 

/**
* database
*/
class DB {

              private $host = DB_HOST;
              private $user = DB_USER;
              private $pass = DB_PASS;
              private $dbname = DB_NAME;

              private $dbh;
              private $error;
              private $stmt;

public  function __construct(){
        // set DSN
    $dsn = 'mysql:host=' . $this->host . ';dbname=' . $this->dbname;
    //set options 
    $options = array(
                   PDO::ATTR_PERSISTENT => true,
                   PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION
        );
    //create a new PDO instance 

    try{
        $this->dbh = new PDO ($dsn, $this->user, $this->pass, $options);
    }  //catch any errors
    catch (PDOException $e) {
        $this->error = $e->getMessage();
    }

    }
    public function query($query){
        $this->stmt = $this->dbh->prepare($query);
    }

    public function bind($param, $value, $type = null){
        if (is_null($type)) {
            switch (true) {
                case  is_int ($value):
                    $type = PDO::PARAM_INT;
                    break;
                case is_bool($value):
                $type = PDO::PARAM_BOOL;
                    break;
                case is_null($value):
                $type = PDO::PARAM_NULL;
                default :
                $type = PDO::PARAM_STR;
            }
        }
        $this->stmt->bindValue ($param, $value, $type);
    }

    public function execute(){

                      return $this->stmt->execute();

    }

    public function resultset(){
                      $this->execute();
                      return $this->stmt->fetchAll(PDO::FETCH_OBJ);

    }

    public function single(){
                      $this->execute();
                      return $this->stmt->fetch(PDO::FETCH_OBJ);
                  }

     public function rowCount(){

                      return $this->stmt->rowCount();
     }
     public function lastInsertId(){
                      return $this->dbh->lastInsertId();
     }     

     public function beginTransaction(){
        return $this->dbh->beginTransaction();
     }  
      public function endTransaction(){
         return $this->dbh->commit();
      }
      public function cancelTransaction(){
         return $this->dbh->rollBack();
      }
    }

-----------------------------------------------------
le fichier topic1.php

?php require('core/ini.php'); ?>

<?php 

$topic = new topic;
$user = new User;

 $topic_id = $_GET['id'];

if (isset($_POST['do_reply'])) {
    $data = array();
    $data['topic_id'] = $_GET['id'];
    $data['body'] = $_POST['body'];
    $data['user_id'] = getUser()['user_id'];

    $validate = new validator;

    $field_array = array('body');

    if ($validate->isRequired($field_array)) {
        if ($topic->reply($data)) {
            redirect('topic1.php?id='.$topic_id.'your reply has been posted', 'success');
        }else{
            redirect('topic1.php?id='.$topic_id.'something wrong with your reply', 'error');
        }
    }else{
        redirect('topic1.php?id='.$topic_id.'your reply form is blank', 'success');
    }
}
$template = new Template('template/topic1.php');

//Assign vars 
$template->topic = $topic->getTopic($topic_id);
$template->replies = $topic->getreplies($topic_id);
$template->title = $topic->getTopic($topic_id)->title;
//display template

// Get template & Assign vars

echo $template;

je cherche a obtenir l'id dans le URL du navligateur atravers la requete $_Get['id'] dans un autre fichier topic1.php

Et ce que j'obtiens comme reponse :

Notice: Undefined index: id in C:\xampp\htdocs\talkingespace\topic1.php on line 8

Fatal error: Uncaught PDOException: SQLSTATE[HY093]: Invalid parameter number: no parameters were bound in C:\xampp\htdocs\talkingespace\librairies\DB.php:61 Stack trace: #0 C:\xampp\htdocs\talkingespace\librairies\DB.php(61): PDOStatement->execute() #1 C:\xampp\htdocs\talkingespace\librairies\DB.php(66): DB->execute() #2 C:\xampp\htdocs\talkingespace\librairies\topic.php(129): DB->resultset() #3 C:\xampp\htdocs\talkingespace\topic1.php(34): topic->getreplies(NULL) #4 {main} thrown in C:\xampp\htdocs\talkingespace\librairies\DB.php on line 61