Applying Even/Odd Classes – Alternate class to each LI foreach

I am trying to give an alternate class to each LI foreach.

i.e.

<li class="odd">
text
</li>
<li class="even">
text
</li>
<li class="odd">
text
</li>
<li class="even">
text
</li>
This is my code:

$toggle = ($toggle=="alignleft"?"alignright":"alignleft");

<ul>
<?php foreach ($this->item->extra_fields as $key=>$extraField): ?>
<?php if($extraField->value): ?>
<li class="<?php echo $toggle; ?>>
Text here
</li>
<?php endif; ?>
<?php endforeach; ?>
</ul>