Like a block's view template, any file in the block's directory can be duplicated in a website's application directory, and will then override that version of the core block. This includes the controller.php file. For example, say you want to change the behavior of the Search block to search just page titles, instead of all the keyword fields on a particular page. The following are the relevant lines of code that will need to be changed:
if (isset($_REQUEST['query'])) {
$ipl->filterByKeywords($_q);
}
This is within the do_search() method. Let's override the core search block controller block type, and change this method to filterByName($_q). First, turn off overrides caching via Dashboard > System & Settings > Optimization > Cache & Speed Settings. Until this is turned off Concrete CMS won't look in the application directory unless it knows it has a file in there.
Next, we create an override directory in application/blocks for the search block. Assuming I'm in my web root directory:
mkdir application/blocks/search
Then, create an empty controller.php in this location. So now now we have an empty file at application/blocks/search/controller.php.
Next, add the proper namespace. Since this is in the Application directory, it looks like this:
<?php
namespace Application\Block\Search;
Then, we add a reference to the core search block controller, which we will be extending:
use Concrete\Block\Search\Controller as SearchBlockController;
Then create the class itself, which extends this search block controller:
class Controller extends SearchBlockController
The entire file now looks like this:
<?php
namespace Application\Block\Search;
use Concrete\Block\Search\Controller as SearchBlockController;
class Controller extends SearchBlockController
{
}
Then, all we have to do is copy the do_search() method from the original core class into this class. All other methods will be inherited from the core search class. Once the method is copied, you can change anything you like this within the class, without having to worry about the other methods in the original core class.