Most Elgg programmers are by now familiar with extending or replacing existing views, or providing new views for new objects etc.

But what if you just wanted to make a simple tweak to an existing view – for example to replace all instances of rude words in a feed article, or to turn passive links into active ones?

Well, fortunately Elgg provides a post processing hook for views which can do just that.

After every view has been generated, the framework will trigger a plugin hook called “‘display’, ‘view’”. This hook is passed a parameter ‘view’ which contains the name of the view being processed (eg. object/blog).

The contents of the view are passed in the $returnvalue variable which you can perform any processing on before returning it from the hook.

I have just uploaded a Trac tags plugin to the Elgg community site which provides a good example of this.

The Trac tags plugin is a tiny plugin which uses the views post processing hook to turn Trac links (e.g. #xxxxx for tickets and [xxxxx] for changesets) into active links into your repository, and here’s how – first we register the hook:

function tractags_init()
{
....
// Register our post processing hook
register_plugin_hook('display', 'view', 'tractags_rewrite');


// define views we want to rewrite codes on (means we don't have to process *everything*)
$CONFIG->tractags_views = array(
'object/thewire',
'object/blog'
);

....
}

Then in our handler looks something like this:

function tractags_rewrite($hook, $entity_type, $returnvalue, $params)
{
global $CONFIG;

$view = $params['view'];

if (($view) && (in_array($view, $CONFIG->tractags_views)))
{
// Search and replace ticket numbers
$returnvalue = preg_replace_callback('/(#)([0-9]+)/i',
create_function(
'$matches',
'
global $CONFIG;

return "<a href=\"{$CONFIG->trac_baseurl}ticket/{$matches[2]}\">{$matches[0]}</a>";
'
), $returnvalue);

// Search and replace changesets
$returnvalue = preg_replace_callback('/(\[)([0-9]+)(\])/i',
create_function(
'$matches',
'
global $CONFIG;

return "<a href=\"{$CONFIG->trac_baseurl}changeset/{$matches[2]}\">{$matches[0]}</a>";
'
), $returnvalue);

return $returnvalue;
}
}

I’m sure you will be able to come up with some much more interesting uses!

Image from the Trac project.