Question

For example, I ask this question and click “Post your question” and stay in the current page. Now I may click the “refresh” button of my browser to see new answers. But I find that on my website, if I click the “refresh” button, a duplicated question will be published. How to avoid this problem?
I am using PHP.

Answer 1

It is common practice after a POST request, to redirect to the same page to avoid this problem.

Lets say you are on /ask_question.php

Your opening <form> tag might look like this:

<form action="/ask_question.php" method="post">

Now, in your /ask_question.php do something like this:

if( isset($_POST['new-question'])){
    // Do your processing here

    // On success:
    header('Location: /ask_question.php');
    exit(); // End the request
}

Update It is important to only redirect after a valid $_POST request has been handled. I test for a form field named new-question but you should use any form field name that has to be present for the $_POST to succeed

This processes their posted data, then on success, redirects back to the same page. The only difference now, is that when they click refresh, no information will be posted.

Note Just make sure nothing is echo‘ed out prior to the header call.