PHP在提交表单后保持选中单选框

<!-- 表单页面 -->
<form action="process_form.php" method="post">
    <input type="radio" name="gender" value="male" <?php echo isset($_POST['gender']) && $_POST['gender'] == 'male' ? 'checked' : ''; ?>> Male
    <input type="radio" name="gender" value="female" <?php echo isset($_POST['gender']) && $_POST['gender'] == 'female' ? 'checked' : ''; ?>> Female
    <input type="submit" value="Submit">
</form>

// process_form.php
<?php
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    // 处理表单数据
    $gender = $_POST['gender'];
    // 可以将数据保存到数据库或会话中
    $_SESSION['gender'] = $gender;
}
?>

<!-- 重新显示表单 -->
<form action="process_form.php" method="post">
    <input type="radio" name="gender" value="male" <?php echo isset($_SESSION['gender']) && $_SESSION['gender'] == 'male' ? 'checked' : ''; ?>> Male
    <input type="radio" name="gender" value="female" <?php echo isset($_SESSION['gender']) && $_SESSION['gender'] == 'female' ? 'checked' : ''; ?>> Female
    <input type="submit" value="Submit">
</form>