在用户刷新网页时阻止表单提交

Question

I have a simple counter for the form button clicks which works well but when the user refreshes the page it adds onto the counter again. I would be grateful if someone would help with the coding I have wrote below.

PHP CODE

<?php
if( isset($_POST['clicks']) ) { 
    incrementClickCount();
}

function getClickCount()
{
    return (int)file_get_contents("clickcount.txt");
}

function incrementClickCount()
{
    $count = getClickCount() + 1;
    file_put_contents("clickcount.txt", $count);
}
?>

HTML and PHP FORM CODE

<form action="<?php $_SERVER['PHP_SELF']; ?>" method="post">
            <input type="submit" value="click me!" name="clicks">
        </form> <div>Click Count: <?php echo getClickCount(); ?></div>

Answer 1

为了防止这种情况，您需要实现POST / REDIRECT / GET模式 。

Answer 2

Just redirect the request to the same page after processing the form post. This can be done as follows in PHP:

<?php header('Location: http://www.example.com/'); ?>

If the user refreshes (after this redirect) nothing would be resubmitted.

Answer 3

Afroze has a good point. Using a header refresh will reset all form data, but it forces the page to refresh twice (when the form is first submitted, and second time when the header forces another refresh). There is another method of preventing a "refresh submission" without forcing a second refresh.

Try this (I'll explain the code below):

<?php
    //begin a session
    session_start();

    //generate a MD5 hash from concatenated form $_POST values
    $formDataHash = md5($_POST['clicks'] . $_POST['otherFormContent']);


    //if form has been submitted before, and the data passed from the form
    //is the same as the previous submission, return false (don't do anything)

    if(isset($_SESSION['formData']) && $_SESSION['formData'] == $formDataHash)
    {
        return false;
    }
    else
    {
        //increase click count
        incrementClickCount();

        //store the submission values
        $_SESSION['formData'] = $formDataHash;
    }

The code above will detect a each form submission, but won't process duplicates. It also won't refresh the page twice (which isn't ideal for users with slow connections).