php MySQLi面向对象的预编译语句

Question

我是php新手，下面是我做的。输出为012345，表示$result= $pre->get_result();有问题。

P.S。我试图在$pre->bind_param('i',$id);使用int而不是String，但它具有相同的输出。

<?php                       
require 'Connections/pplcon.php';
header("Content-Type:text/html; charset=utf-8");
mysqli_set_charset( $conn, 'utf8');
?> 


<?php

/* activate reporting */
$driver = new mysqli_driver();
$driver->report_mode = MYSQLI_REPORT_ALL;


$id="1";

    //Created a template
    echo 0; 
    $sql = "SELECT * FROM Coupon WHERE ActivityID = ?";
    //Create a prepared statement
    echo 1; 
    if($pre = $conn->prepare($sql)) {
        echo 2; 
        $pre->bind_param('s',$id);
        echo 3; 

        echo 4; 
        $pre->execute();
        echo 5; 
        $result= $pre->get_result();
        echo 6; 
        if ($result->num_rows > 0) {
                while ($row = mysqli_fetch_assoc($result)) {
                    echo $row['ActivityID'] . "<br>";
                }

        }
    }
    else {
        echo 0; 
    }

?>