Fortunately the application is now an open source project available on Google Code and it was only a short matter of time before someone came up with a fix – thank you Howard.

One plugin I recommend that everyone should add to their WordPress installation is the Google XML Sitemaps plugin.

This plugin will automatically generate an XML sitemap of your posts and pages and ping supporting search engines to notify them that the sitemap has been updated.

But the best thing about this plugin for other plugin developers is it provides hooks so you can ‘borrow’ it’s functionality so that your plugin can add additional pages into the XML sitemap that is generated.

So if you’re a WordPress plugin developer, read on…

How to add pages to the XML sitemap

To illustrate how to implement the XML Sitemaps hook, I will base the example on the WP e-Commerce plugin (please note, I originally implemeted this with version 3.6.12 of the WP e-Commerce plugin so it may not work with more recent versions). We will create a function that will add all of this plugin’s product pages into the XML sitemap produced by Google XML Sitemaps.

The Google XML Sitemaps plugin provides the hook “sm_buildmap” which gets triggered whenever the plugin re-builds the sitemap file. We are going to create a function “wp_ecommerce_sm” which will get called by this hook.

So, here’s the function code:

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function wp_ecommerce_sm() {
   global $wpdb;
   if ( class_exists('GoogleSitemapGenerator') ) {
      $generatorObject = &GoogleSitemapGenerator::GetInstance();
      $sql = "SELECT DISTINCT * FROM `" . $wpdb->prefix . "product_list` WHERE `active` IN('1') ORDER BY `id` DESC";
      $product_list = $wpdb->get_results($sql, ARRAY_A);
      foreach ( $product_list as $product ) {
         $purchase_link = wpsc_product_url($product['id']);
         $purchase_link = str_replace('&', '&', $purchase_link);
         if ($generatorObject != null) $generatorObject->AddUrl($purchase_link, time(), "daily", 0.5);
      }
   }
}
add_action("sm_buildmap", "wp_ecommerce_sm");

The main points to note in this function are…

Check that the Google XML Sitemaps exists (is installed):

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if ( class_exists('GoogleSitemapGenerator') ) {

Get an instance of the Google XML Sitemap plugin:

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$generatorObject = &GoogleSitemapGenerator::GetInstance();

Loop through all our additional pages that we want to add to the sitemap, in this case the WP e-Commerce product pages:

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$sql = "SELECT DISTINCT * FROM `" . $wpdb->prefix . "product_list` WHERE `active` IN('1') ORDER BY `id` DESC";
$product_list = $wpdb->get_results($sql, ARRAY_A);
foreach ( $product_list as $product ) {
   // Add pages to sitemap here
}

And within our loop, add our pages like this:

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if ($generatorObject != null) $generatorObject->AddUrl($purchase_link, time(), "daily", 0.5);

And lastly we need to add the hook to call this function whenever the XML sitemap is rebuilt:

add_action("sm_buildmap", "wp_ecommerce_sm");

Is that all there is to it?

Well, not really. Your still have to trigger the sitemap to re-build to include your new pages. You can do this manually by going to your XML Sitemaps setting page and clicking the link to rebuild to force the sitemap to re-build. Ideally however you would try to get your plugin to do this automatically whenever you add/edit/delete one of your pages. I couldn’t find an obvious hook to easily do this so that is something I would like to see adding in a future version of the Google XML Sitemaps plugin.

Download

Download the above code packaged as a WordPress plugin using the link below:

Loading XML files in Flash over an SSL Connection fails in Internet Explorer if the Pragma:no-cache or Cache-control:no-cache HTTP headers are set on the XML file. By default, all dynamically generated files are returned by the server with the Pragma:no-cache header so that they are not cached by the browser.

To ensure that Flash loads the XML successfully, you should use the following function in PHP near the top of your code:

session_cache_limiter('private_no_expire');