How to remember checkbox input in PHP Forms

Question

For usability purposes I like to set up my form fields this way:

<?php

$username = $_POST['username'];
$message  = $_POST['message'];

?>

<input type="text" name="username" value="<?php echo $username; ?>" />

<textarea name="message"><?php echo $message; ?></textarea>

This way if the user fails validation, the form input he entered previously will still be there and there would be no need to start from scratch.

My problem is I can't seem to keep check boxes selected with the option that the user had chosen before (when the page refreshes after validation fails). How to do this?

Answer 1

<input type="checkbox" name="somevar" value="1" <?php echo $somevar ? 'checked="checked"' : ''; ?>/>

Also, please consider sanitising your inputs, so instead of:

$somevar = $_POST['somevar'];

...it is better to use:

$somevar = htmlspecialchars($_POST['somevar']);

Answer 2

My first suggestion would be to use some client-side validation first. Maybe an AJAX call that performs the validation checks before continuing.

If that is not an option, then try this:

<input type="checkbox" name="subscribe" <?php echo (isset($_POST['subscribe'])?'checked="checked"':'') ?> />

So if subscribe is = 1, then it should select the box for you.

Answer 3

When the browser submits a form with a checked checkbox, it sends a variable with the name from the name attribute and a value from the value attribute. If the checkbox is not checked, the browser submits nothing for the checkbox. On the server side, you can handle this situation with array_key_exists(). For example:

<?php
$checkedText = array_key_exists('myCheckbox', $_POST) ? ' checked="checked"' : '';
?>
<input type="checkbox" name="myCheckbox" value="1"<?php echo $checkedText; ?> />

Using array_key_exist() avoids a potential array index undefined warning that would be issued if one tried to access $_POST['myCheckbox'] and it didn't exist.

Answer 4

You may add this to your form:

<input type="checkbox" name="mycheckbox" <?php echo isset($_POST['mycheckbox']) ? "checked='checked'" : "" ?> />

isset checks if a variable is set and is not null. So in this code, checked will be added to your checkbox only if the corresponding $_POST variable has a value..