雖然我上登錄按鈕點擊然後致命錯誤發生呼叫成員函數執行（）

Question

雖然我上登錄按鈕然後致命錯誤單擊：在C:\wamp\www\json\login.php

Call to a member function execute() on a non-object

該誤差發生線路24。

我做了更改，但不起作用。​​方法無法正常工作。

login.php文件

<?php 
require("config.inc.php"); 
if (!empty($_POST)) { 
$query = "SELECT id,username,password FROM users WHERE username = :username"; 
$query_params = array(
':username' => $_POST['username'] 
); 
try { 
$stmt = $db->prepare($query); 
$result = $stmt->execute($query_params); 
} 
catch (PDOException $ex) { 
$response["success"] = 0; 
$response["message"] = "Database Error1. Please Try Again!"; 
die(json_encode($response)); 
} 
$validated_info = false; 
$row = $stmt->fetch(); 
if ($row) { 
if ($_POST['password'] === $row['password']) { 
$login_ok = true; 
} 
} 
if ($login_ok) { 
$response["success"] = 1; 
$response["message"] = "Login successful!"; 
die(json_encode($response)); 
} else { 
$response["success"] = 0; 
$response["message"] = "Invalid Credentials!"; 
die(json_encode($response)); 
} 
} else { 
?> 
<h1>Login</h1> 
<form action="login.php" method="post"> 
Username:<br /> 
<input type="text" name="username" placeholder="username" /> 
<br /><br /> 
Password:<br /> 
<input type="password" name="password" placeholder="password" value="" /> 
<br /><br /> 
<input type="submit" value="Login" /> 
</form> 
<a href="register.php">Register</a> 
<?php 
} 
?> 

config.inc.php文件

<?php 
$db = mysqli_connect('localhost','root','','json') or die(mysqli_error($connection)); 
?> 

database： -

CREATE TABLE IF NOT EXISTS `users` (
    `id` int(11) NOT NULL AUTO_INCREMENT, 
    `username` varchar(255) NOT NULL, 
    `password` varchar(255) NOT NULL, 
    PRIMARY KEY (`id`) 
) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=2 ; 

-- 
-- Dumping data for table `users` 
-- 

INSERT INTO `users` (`id`, `username`, `password`) VALUES 
(1, 'admin', 'admin'); 

Answer 1

看這個examples 嘗試使用

$stmt->bind_param(...);