mysqli类中的undefined属性

Question

我一直在学习关于php的oop，我一直在尝试创建一个类，我可以使用$ data-＆gt; uname从数据库中获取信息; 但是当我创建我的课程时，我得到了一个

( ! ) Notice: Undefined property: UserData::$uname in C:\wamp\www\header.php on line 264

错误

header.php第264行只是

<?php $data->uname; ?>

我的课程从文件顶部开始

$data = new UserData($_SESSION['id']);

classfile是

<?php
require_once("functions/connect.php");
class UserData{
    public $db;

    public function __construct(){
        $this->db = new mysqli(DB_SERVER, DB_USERNAME, DB_PASSWORD, DB_DATABASE);
        if(mysqli_connect_errno()){
            echo "Could not establish connection";
            exit;
        }
    }
    function data($id){
        $stmt = $this->db->prepare("SELECT * FROM users WHERE uid = ?");
        $stmt->bind_param("i",$id);
        $stmt->execute();
        $result = $stmt->get_result();
        $users = $result->fetch_assoc();
        foreach ($users as $obj => $value){
            $this->$obj = $value; 
        }
    }
}