在非对象 MySQLi 上调用成员函数 bind_param()

Okay, so I'm trying to update a blog entry, and I'm getting Call to a member function bind_param() on a non-object when I try to run the script. I have done extensive research to see if I could fix it myself, but I must be missing something.

<?php
$stmt = $mysqli->prepare("UPDATE blogentries SET 
  headline = ?, 
   image = ?, 
   caption = ?,  
   article = ?
    WHERE id = ?");
$stmt->bind_param('ssssi',
   $_POST['headline'],
   $_POST['image'],
   $_POST['caption'],
   $_POST['article'],
   $_POST['id']);
$stmt->execute(); 
$stmt->close();

?>

提前致谢，

奥斯汀

更新:这是数据库连接

我添加了额外的 $mysqli 连接用于调试目的，即使没有它也会发生错误.

if ($stmt = $mysqli->prepare(...)) {
    $stmt->bind_param(...);
    ...
}
else {
    printf("Errormessage: %s
", $mysqli->error);
}