解决PHP中$_POST无法获取表单提交数据的常见问题

<?php
// ... 其他PHP逻辑 ...

// 按钮的生成逻辑
if (isset($_GET['trn']) && $_GET['trn']=='UPDATE'){
echo '<button type="submit" class="btn btn-primary addOrder" name="UpdateBtn">Update list</button>';
}else{
echo '<button type="submit" class="btn btn-primary addOrder" name="AddOrder">Add list</button>';
}
?>

<!-- ... 中间可能存在其他HTML结构 ... -->

<div class="row inputRow">
    <!-- 输入字段 -->
    <div class="col-2">
    <h5> first name<h5>
    <input type="text" class="form-control"  placeholder="fname" name="fname" value="<?php if (isset($_GET['trn']) && $_GET['trn']=='UPDATE'){ echo $fname;} ?>">
    </div>
    <!-- ... 其他输入字段 ... -->
    <div class="col-6">
    <h5> User type<h5>
        <select class="form-select" aria-label="Default select example" name="type">
            <option value="administrator" <?php if (isset($_GET['trn']) && $_GET['trn']=='UPDATE' && $id=='administrator'){ echo 'selected';} ?>>administrator</option>
            <option value="customer" <?php if (isset($_GET['trn']) && $_GET['trn']=='UPDATE' && $id =='customer'){ echo 'selected';} ?>>customer</option>
        </select>
    </div>
</div>

<form action="" method="post" >            
    <div class="row inputRow">
        <div class="col-2">
            <h5> first name<h5>
            <input type="text" class="form-control"  placeholder="fname" name="fname" value="<?php if (isset($_GET['trn']) && $_GET['trn']=='UPDATE'){ echo $fname;} ?>">
        </div>
        <div class="col-2">
            <h5> last name<h5>
            <input type="text" class="form-control"  placeholder="lname" name="lname" value="<?php if (isset($_GET['trn']) && $_GET['trn']=='UPDATE'){ echo $lname;} ?>">
        </div>
        <div class="col-2">
            <h5> username<h5>
            <input type="text" class="form-control"  placeholder="username" name="username" value="<?php if (isset($_GET['trn']) && $_GET['trn']=='UPDATE'){ echo $username;} ?>">
        </div>
        <div class="col-2">
            <h5> password<h5>
            <input type="text" class="form-control"  placeholder="password" name="password" value="<?php if (isset($_GET['trn']) && $_GET['trn']=='UPDATE'){ echo $password;} ?>">
        </div>
        <div class="col-6">
            <h5> User type<h5>
            <select class="form-select" aria-label="Default select example" name="type">
                <option value="administrator" <?php if (isset($_GET['trn']) && $_GET['trn']=='UPDATE' && $id=='administrator'){ echo 'selected';} ?>>administrator</option>
                <option value="customer" <?php if (isset($_GET['trn']) && $_GET['trn']=='UPDATE' && $id =='customer'){ echo 'selected';} ?>>customer</option>
            </select>
        </div>
        <?php
        if (isset($_GET['trn']) && $_GET['trn']=='UPDATE'){
        echo '<button type="submit" class="btn btn-primary addOrder" name="UpdateBtn">Update list</button>';
        }else{
        echo '<button type="submit" class="btn btn-primary addOrder" name="AddOrder">Add list</button>';
        }
        ?>
    </div>
</form>

<?php
// 假设 $pdo 已经初始化，并且 $id 变量已从 $_GET 或其他方式获取
// require_once 'db_config.php'; // 包含数据库配置和连接
// $pdo = connect_db(); // 连接数据库

if (isset($_POST['UpdateBtn'])) {
    // 验证和过滤输入数据是至关重要的安全实践
    $fname = htmlspecialchars($_POST['fname']);
    $lname = htmlspecialchars($_POST['lname']);
    $username = htmlspecialchars($_POST['username']);
    $password = password_hash($_POST['password'], PASSWORD_DEFAULT); // 密码应哈希存储
    $type = htmlspecialchars($_POST['type']);

    // 调用更新函数
    updatelist($pdo, $id, $fname, $lname, $username, $password, $type);
}

// updatelist 函数定义，通常放在单独的 PHP 文件中
function updatelist($pdo, $id, $fname, $lname, $username, $password, $type) {
    try {
        $sql = 'UPDATE users SET fname=:fname, lname=:lname, username=:username, password=:password, type=:type WHERE id=:id';
        $statement = $pdo->prepare($sql);
        // 绑定参数以防止SQL注入
        $statement->bindValue(':id', $id);
        $statement->bindValue(':fname', $fname);
        $statement->bindValue(':lname', $lname);
        $statement->bindValue(':username', $username);
        $statement->bindValue(':password', $password);
        $statement->bindValue(':type', $type);
        $statement->execute();

        echo '<script>alert("Order successfully updated")</script>';
        echo '<script>window.location="page2.php"</script>'; // 重定向到其他页面
    } catch (PDOException $e) {
        // 错误处理
        error_log('Database Update Error: ' . $e->getMessage()); // 记录错误到日志
        echo 'Message: An error occurred during update. Please try again later.';
        // 生产环境中不直接显示详细错误信息给用户
    }
}
?>