Delegates allow developers to manipulate input and output and perform other tasks during the generation of back-end and front-end pages.
Delegates are functions in Symphony's core that allow extension developers to intervene at key moments in the generation of a back-end or front-end Symphony page. The delegate will usually provide a contextually relevant PHP object (for instance a page object or an event object) that the developer can then work with and pass back to the system for further processing.
Extensions can subscribe to delegates by declaring a getSubscribedDelegates() function in the extension.driver.php file, like this:
public function getSubscribedDelegates()
{
return array(
array(
'page' => '/delegatepage/',
'delegate' => 'DelegateName',
'callback' => 'extensionFunction'
),
);
}getSubscribedDelegates() is expected to return an array of subscriptions, each of which is an array consisting of three key/value pairs: page, delegate, and callback. The first two values are defined by the delegate itself. The last value is the name of a callback function provided by the extension.
During normal system processing, delegates fire notifyMembers() functions, which allows any subscribed extensions to intervene before processing continues.
Please refer to the API documentation on delegates for a complete list of delegates. Every entry links to the GitHub-hosted copy of the file where the delegate is defined. If you want to know in which version a delegate was first introduced, click through to the file and check the delegate's @since parameter.