PHP+SQLite答题系统分数页两类警告错误的修复方法

错误原因分析 #

1. 第95行：Trying to access array offset on value of type null
   提交最后一道题后，$currentQuestion已变为null，但POST处理代码仍尝试访问$currentQuestion['Correct']，触发数组偏移量访问错误。

2. 第103行：Undefined array key "questionIndex"
   所有题目完成后，代码会执行unset($_SESSION['questionIndex'])，若此时用户刷新页面或触发POST请求，访问未定义的session键就会抛出警告。

修复步骤 #

1. 调整POST请求处理顺序：将POST逻辑移到session初始化和页面渲染之前，确保提交请求时能正确获取当前题目数据。
2. 增加空值检查：访问$currentQuestion的数组键前，先确认它不为null。
3. session变量安全访问：读取session中的questionIndex和score时，增加存在性检查，避免未定义键警告。

修复后的完整代码 #

<?php
session_start();

class MyDB extends SQLite3
{
    function __construct()
    {
        $this->open('questions.db');
    }
}

// 先处理POST提交请求
if ($_SERVER['REQUEST_METHOD'] === 'POST' && isset($_POST['submit'])) {
    // 确保session中的核心数据存在
    if (isset($_SESSION['questions'], $_SESSION['questionIndex'], $_SESSION['score'])) {
        $questions = $_SESSION['questions'];
        $questionIndex = $_SESSION['questionIndex'];
        $currentQuestion = (!empty($questions) && $questionIndex < count($questions)) ? $questions[$questionIndex] : null;
        
        if ($currentQuestion !== null) {
            $userAnswer = isset($_POST['answer']) ? $_POST['answer'] : '';
            $correctAnswer = $currentQuestion['Correct'];
            
            if ($userAnswer == $correctAnswer) {
                $_SESSION['score']++;
            }
        }
        
        // 移动到下一题，判断是否还有剩余题目
        if ($_SESSION['questionIndex'] < count($_SESSION['questions']) - 1) {
            $_SESSION['questionIndex']++;
        } else {
            // 标记答题完成
            $_SESSION['quizCompleted'] = true;
        }
    }
    // 重定向避免刷新重复提交
    header("Location: " . $_SERVER['PHP_SELF']);
    exit();
}

// 初始化session数据
$db = new MyDB();
if (!$db) {
    echo $db->lastErrorMsg();
}

// 若未初始化题目或答题已完成，重置session并重新加载题目
if (!isset($_SESSION['questions']) || isset($_SESSION['quizCompleted'])) {
    unset($_SESSION["questions"]);
    unset($_SESSION['score']);
    unset($_SESSION['questionIndex']);
    unset($_SESSION['quizCompleted']);
    
    $sql = "SELECT * FROM questions";
    $result = $db->query($sql);

    $_SESSION['questions'] = [];
    while ($row = $result->fetchArray(SQLITE3_ASSOC)) {
        $_SESSION['questions'][] = $row;
    }

    $_SESSION['score'] = 0;
    $_SESSION['questionIndex'] = 0;
}

// 准备当前题目数据
$questions = $_SESSION['questions'];
$questionIndex = isset($_SESSION['questionIndex']) ? $_SESSION['questionIndex'] : 0;
$currentQuestion = (!empty($questions) && $questionIndex < count($questions)) ? $questions[$questionIndex] : null;

// 渲染页面内容
if ($currentQuestion !== null) {
    echo "<h1>" . $currentQuestion['QID'] . ") " . $currentQuestion['Stem'] . "</h1><br> ";
    echo "<form method='post'>";
    echo "<input type='radio' name='answer' value='A'>" . $currentQuestion['Alt_A'] . "<br>";
    echo "<input type='radio' name='answer' value='B'>" . $currentQuestion['Alt_B'] . "<br>";
    echo "<input type='radio' name='answer' value='C'>" . $currentQuestion['Alt_C'] . "<br>";
    echo "<input type='radio' name='answer' value='D'>" . $currentQuestion['Alt_D'] . "<br>";
    echo "<button type='submit' name='submit'>Submit</button>";
    echo "</form>";
} else {
    echo "<h2>Your Score: " . (isset($_SESSION['score']) ? $_SESSION['score'] : 0) . "</h2>";
    // 添加重新答题按钮
    echo "<form method='post'><button type='submit' name='submit'>Restart Quiz</button></form>";
}

$db->close();
?>

额外优化说明 #

• 增加POST重定向，解决页面刷新重复提交答案的问题。
• 添加quizCompleted标记，确保答题完成后能正确重置session状态。
• 所有session变量访问均增加存在性检查，彻底消除未定义键警告。

内容的提问来源于stack exchange，提问作者Samitt