Multi-page PHP Form With back Button issue

Question

I have created a muilti-page PHP form that inserts the results into a MySQl database and works fine, the only issue I have is when I try to go back I get the 'Confirm Form Resubmission''ERR_CACHE_MISS' error page.

Php isn't my strongest language and need a bit of help with fixing it.

its a 20 page survey with each page having radio buttons with a choice of 1 to 10.

Sample of my code below, any advice would be great.

Cheers

<?php session_start();
$_SESSION['answer_04'] = $_POST['answer_04'];
?>

<form action="peem-05.php" id="peem" method="post">

<ul class="answers">
    <li class="group1"><input type="radio" id="radio1" name="answer_05" value="1" data-msg-required="Please choose an answer bewteen 1 and 10" required><label for="radio1"><br>1</label></li>
    <li class="group1"><input type="radio" id="radio2" name="answer_05" value="2" required><label for="radio2"><br>2</label></li>
    <li class="group2"><input type="radio" id="radio3" name="answer_05" value="3" required><label for="radio3"><br>3</label></li>
    <li class="group2"><input type="radio" id="radio4" name="answer_05" value="4" required><label for="radio4"><br>4</label></li>
    <li class="group3"><input type="radio" id="radio5" name="answer_05" value="5" required><label for="radio5"><br>5</label></li>
    <li class="group3"><input type="radio" id="radio6" name="answer_05" value="6" required><label for="radio6"><br>6</label></li>
    <li class="group4"><input type="radio" id="radio7" name="answer_05" value="7" required><label for="radio7"><br>7</label></li>
    <li class="group4"><input type="radio" id="radio8" name="answer_05" value="8" required><label for="radio8"><br>8</label></li>
    <li class="group5"><input type="radio" id="radio9" name="answer_05" value="9" required><label for="radio9"><br>9</label></li>
    <li class="group5"><input type="radio" id="radio10" name="answer_05" value="10" required><label for="radio10"><br>10</label></li>
</ul>


<a href="javascript:history.back(1)"><img class="backButton" src="img/back-button.png"/></a>

<button class="rightArrow" name="submit" type="submit" value="Next" ><img class="backButton" src="img/next-button.png"/></button>
</form>

Answer 1

Instead of using javascript:history.back(1) you better save data to PHP Session and going back means re-visiting same page.

[save.php]

$step = $_POST['formStep'];
$formData = $_POST['Form'][$step]; // all values from form
$formID = $_POST['formID']; // validate

if ($formData && $step) {
    if ($step < $maxSteps) {
        $_SESSION[$formID][$step] = $formData;

        $this->showStep($step++);
    } else {
        $this->db->saveForm($_SESSION[$formID]);
    }
}

[showStep.php]

$step = isset($_REQUEST['step']) ? $_REQUEST['step'] : 1;
$formID = isset($_SESSION['formID']) ? $_SESSION['formID'] : rand(0, 99);
$formData = isset($_SESSION[$formID][$step]) ? $_SESSION[$formID][$step] : [];
?>
<form action="save.php?step=<?= $step; ?>">
    <input type="hidden" value="<?= $formID; ?>" name="formID"/>
    <?php switch ($step): ?>
<?php case 1: ?>
      <input type="radio" id="radio10" name="Form[<?= $formID; ?>][<?= $step; ?>][answer_05]" value="10" <?= isset($formData['answer_05']) ? 'checked="checked"' : ''; ?>/>
<?php case 20: ?>
      ...
<?php break; ?>
</form>
<a href="showStep.php?step=<?= $step - 1; ?>">Back</a>

Answer 2

Note that you have to rename your peem-x.php files removing the zero to make that code work. I commented my changes, maybe this helps you.

<?php
session_start();

$page = basename(__FILE__); // get current filename
$page = preg_replace("/[^0-9]/","",$page); // remove everything except numbers
$page_last = "peem-".($page-1).""; // calculate last page name
$page_now = "peem-".$page.""; // current page name

for ($i = 0; $i < count($_POST['answer']); $i++) { // loop for total count of answers selected
    $_SESSION['page'.$page_now.'']['answer'.$i.''] = $_POST['answer'.$i.''];  // assign session to answer
}
?>

<form action="" id="peem" method="post">

    <ul class="answers">
        <li>Please choose an answer between 1 and 10</li>
        <?php
        for ($i = 1; $i < 10; $i++) {
            // check every loop if it's the current page and current answer that has been checked before
            // if so, set a variable to mark it as checked
            if ($_SESSION['page'] == $page_now && $_SESSION['page']['answer'.$i.''] == 'page'.$page_now.'answer'.$i.'')
            {
                $checked = " checked"; // create var to check current answer in loop
            }

            echo '<li class="group1"><input type="radio" id="radio1" name="answer' . $i . '" value="1"'.$checked.'><label for="radio' . $i . '"><br>' . $i . '</label></li>';
            unset($checked); // unset $checked var for next loop to avoid checking unchecked radio buttons
        }
        ?>
    </ul>


    <a href="-<?php echo $page_last; ?>.php"><img class="backButton" src="img/back-button.png"/></a>

    <button class="rightArrow" name="submit" type="submit" value="Next" ><img class="backButton" src="img/next-button.png"/></button>
</form>

<?php
// test session and post variables
echo "<pre>";
print_r($_POST);
print_r($_SESSION);
echo "</pre>";
?>