Easy theme switching?

Somebody contacted me to ask about this code, and how to get it working. I've made some changes, more for my own benefit such as changing $tema to $style etc.

Thanks to ufku for his original example code.

The code that goes inside the module, called access_theme.module
Call it whatever you want but match the function names in the module too.

<?php
// $Id$
/**
 * Implementation of hook_help().
 */
function access_theme_help($section) {
  switch ($section) {
    case 'admin/help#access_theme':
      return t('This module enables the switching of a theme for non authenticated users. It can be used to present an accessible theme (text only?) as a text link.');
    case 'admin/modules#description':
      return t('A module to easily switch themes');
    // OPTIONAL: Add additional cases for other paths that should display help text.
  }
}

/**
 * Implementation of hook_init().
 */
function access_theme_init() {
//switch theme
if (($style=$_GET['style']) && $style!=$_SESSION['style']) {//if it isnt the current theme.
  $themes = list_themes();// get avaliable themes.
  if ($themes[$style]) {//theme is valid.
    $_SESSION['style'] = $style;
  }
}
//set theme
if ($_SESSION['style'] && $_SESSION['style']!=$GLOBALS['user']->theme) {
  $GLOBALS['custom_theme'] = $_SESSION['style'];
}
}

Put it in your module folder and enable it.

I then created a custom block because I needed to hard code some access keys. It does the job for me.
I created a new block (input type php), inserted the code below. I enabled the block in a region in this case a custom region called 'support links'.

<ul id="navlist">
<li><a href="/" title="Home" accesskey="1">Home</a></li>
	<?php
	//'clubmark' is the name of the graphic theme I created
	//'text_only' is the name of the errrrrr text only theme I created
	//I use nofollow on the theme switcher links to prevent indexing of duplicate pages for text only (just a thought)
	$switch = $GLOBALS['theme']=='clubmark' ? 'text_only' : 'clubmark';//get the theme which is not in use.
	$uri = str_replace('&style='.$GLOBALS['theme'], '', request_uri());//clean uri to prevent multiple style=... strings
	if ( $GLOBALS['theme']=='text_only' )
	{
		$style = '<a href="'.$uri.'&style='.$switch.'" title="'.t('select graphic theme').'" rel="nofollow">Graphic Version</a>';
	}
	else
	{
		$style = '<a href="'.$uri.'&style='.$switch.'" title="'.t('select text only theme').'" rel="nofollow">Text Only Version</a>';
	}
	?>
<li><?php print $style; ?></li>
<li><a href="/accessibility" title="Accessibility options for this site" accesskey="0">Accessibility</a></li>
<li><a href="/search" title="Advanced search options" accesskey="4">Search</a></li>
<li><a href="/contact-us" title="Contact Clubmark or give feedback on this site" accesskey="9">Contact Us</a></li>
<li><a href="/faq" title="Frequently Asked Questions about Clubmark Accreditation" accesskey="5">FAQ</a></li>
<li><a href="/sitemap" title="Sitemap links for this site" accesskey="3">Sitemap</a></li>
<li><a href="/terms-and-conditions" title="Terms and conditions for using clubmark.org.uk" accesskey="8">Terms &amp; Conditions</a></li>
</ul>

Alternatively you can place the following code somewhere in each theme page.tpl.php
This puts the link in the Primary Nav, but it doesn't change the text link - should be easy enough to adapt though, using the if else statement from above.

<?php 
$switch = $GLOBALS['theme']=='clubmark' ? 'text_only' : 'clubmark';//get the theme which is not in use.
$uri = str_replace('&style='.$GLOBALS['theme'], '', request_uri());//clean uri to prevent multiple style=... strings
$style = '<a href="'.$uri.'&style='.$switch.'" title="'.t('select different theme').'"><div style="background: url('.$base_path.'modules/zzhack/'.$switch.'.png) no-repeat 50% 50%; width: 20px;">swiitch style</div></a>';
@array_unshift($primary_links, $style);
?>

The text only module is basically a duplication of my graphic theme with some preg_replace to strip out images and replace with the alt text.

eg. in block.tpl.php

<h2><?php print $block->subject; ?></h2>
<div class="content">
<?php
$pattern = '/<img[^>]*?((alt="(.*?)".*?>)|>)/i';
$replacement = '(Image: $3)';
print preg_replace($pattern, $replacement, $block->content);
?>
</div>

In use on a site:
http://www.clubmark.org.uk

Mark