Event

The 'Event' class allows you to register handlers for named events. It also allows you to invoke ('fire') the events on demand. This provides you with a mechanism for sending signals or sharing data between loosely coupled blocks of code. It also allows you to configure 'hooks' within a code base so you can easily extend or override the behaviour of an application.

Usage

Bind and Fire

Use the bind method to register a handler (a callback function) for an event.

Each execution of the method will add an additional callback. The callbacks are executed in the order they are defined.

Event::bind('router.match', function() {
  return "The event 'router.match' was called.";
});

Event::bind('router.match', function() {
  // Log data...
  return "Routing data was logged.";
});

Use the fire method to trigger all callback functions for an event. The method returns an array containing the responses from all of the event handlers (even empty responses).

// Trigger the 'router.match' event:
$responses = Event::fire('router.match');

// Result:
$responses = array(
  "The event 'router.match' was called.",
  "Routing data was logged."
);

To only execute a callback once, irrespective of the number of times the event is fired, when registering an event handler, call the bind method with a third argument of TRUE:

// Only execute this handler once.
Event::bind('router.match', function() {
  return "The event 'router.match' was called.";
}, TRUE);

// Execute this handler every time.
Event::bind('router.match', function() {
  // Log data...
  return "Routing data was logged.";
});

Now if the event is fired twice, the first handler will only be called once:

// Trigger the 'router.match' event twice:
$one = Event::fire('router.match');
$two = Event::fire('router.match');

// Results:
$one = array(
  "The event 'router.match' was called.",
  "Routing data was logged."
);

$two = array(
  "Routing data was logged."
);

You can easily pass data to the registered callback functions when firing an event:

// Register a handler that expects two parameters:
Event::bind('log', function($log, $data) {
  // Write $data to a $log.
});

// Pass data to the event handler:
Event::fire('log', array('log.txt', 'Something happened.'));

Append and Insert

The append method is an alias for the bind method; both add event handlers to the end of the list of existing handlers.

The insert method takes the same parameters as bind, but adds the event handler to the start of the queue, ensuring it is executed before any of the other callback functions.

First and Until

The first method triggers all callback functions for an event and returns only the first response (even if it is empty). As the method returns only a single value, the result is not wrapped in an array.

// Returns: "The event 'router.match' was called."
$response = Event::first('router.match');

The until method is very similar to the first method, but it returns the first non-empty response.

Bound, Fired and Reset

Use the bound method to check if any handlers are registered for an event:

// Returns: TRUE.
$bound = Event::bound('router.match');

Use the names method to retrieve all events that have any handlers registered:

// Returns: Array
$bound_events = Event::names();

Use the fired method to check if an event has fired:

// Fire the event:
Event::fire('router.match');

// Returns: TRUE.
$fired = Event::fired('router.match');

Use the reset method to clear the flag indicating an event has fired. If called without an argument, all event counters are reset.

// Clear the 'fire' count for the event:
Event::reset('router.match');

// Returns: FALSE.
$times = Event::fired('router.match');

Rebind and Unbind

The rebind method takes the same parameters as bind, but it will overwrite all existing handlers defined for an event with a new callback function.

The unbind method deregisters the handlers for an event:

// Remove all callback functions bound to the event:
Event::unbind('router.match');

// Returns NULL as all handlers have been removed:
Event::fire('router.match');

If called without an argument, the unbind method will remove the handlers for all events.