Aura Signal
The Aura Signal package is a SignalSlots/EventHandler implementation for PHP. With it, we can invoke handlers ("slots" or "hooks") whenever an object sends a signal ("notification" or "event") to the signal manager.
Basic Usage
Instantiating the Signal Manager
First, instantiate the signal Manager
class. The easiest way to do this is to call the Aura.Signal/scripts/instance.php
script.
<?php
$signal = require '/path/to/Aura.Signal/scripts/instance.php';
Adding Signal Handlers
Before we can send a signal to the Manager
, we will need to add a handler for it. To add a handler, specify:
-
The class expected to be sending the signal. This can be
'*'
for "any class", or a fully-qualified class name. -
The name of the signal.
-
A closure or callback to handle the signal.
For example, to add a closure that will be executed every time an object of the class Vendor\Package\Example
sends a signal called 'example_signal'
:
<?php
$signal->handler(
'Vendor\Package\Example',
'example_signal',
function ($arg) { echo $arg; }
);
Signals By Class
To send a signal, the sending class must have an instance of the Manager
. The class should call the send()
method with the originating object (itself), the signal being sent, and arguments to pass to the signal handler.
For example, we will define the Vendor\Package\Example
class, and have it send a signal to the Manager
.
<?php
namespace Vendor\Package;
use Aura\Signal\Manager as SignalManager;
class Example
{
protected $signal;
public function __construct(SignalManager $signal)
{
$this->signal = $signal;
}
public function doSomething($text)
{
echo $text;
$this->signal->send($this, 'example_signal', $text);
}
}
Now whenever we call the doSomething()
method, it will send the 'example_signal'
to the Manager
, and the Manager
will invoke the handler for that signal.
Signal Inheritance
If a class sends a signal, and no handler has been set for it, then the Manager
will do nothing. However, if a handler has been set for a parent class, and one of its child classes sends a signal handled for the parent, the Manager
will handle that signal for the child as well.
For example, if we have these two classes, and call doSomethingElse()
on each of them ...
<?php
namespace Vendor\Package;
use Aura\Signal\Manager as SignalManager;
class ExampleChild extends Example
{
public function doSomethingElse($text)
{
echo $text . $text . $text;
$this->signal->send($this, 'example_signal', $text);
}
}
class ExampleOther
{
protected $signal;
public function __construct(SignalManager $signal)
{
$this->signal = $signal;
}
public function doSomethingElse($text)
{
echo $text . $text . $text;
$this->signal->send($this, 'example_signal', $text)
}
}
... then the Manager
will handle the signal from ExampleChild
because its parent has a handler for it. The Manager
will not handle the signal for ExampleOther
because no handlers for it or its parents have been added to the Manager
.
Signals By Object
It is possible to tie a handler to an object instance, so that only signals sent from that specific object will be handled. To do so, pass the object instance as the $sender
for the handler.
<?php
/**
* @var Aura\Signal\Manager $signal
*/
$object = new Vendor\Package\ExampleChild($signal);
$signal->handler(
$object,
'example_signal',
function ($arg) { echo "$arg!!!";}
);
If that specific object instance sends the example_signal
then the handler will be triggered, but no other instance of ExampleChild
will trigger the handler when it sends the same signal. This is useful for setting signal handlers from within an object that contains its own callback; for example:
<?php
namespace Vendor\Package;
use Aura\Signal\Manager as SignalManager;
class ExampleAnotherChild extends Example
{
public function __construct(SignalManager $signal)
{
parent::__construct();
$this->signal = $signal;
$this->signal->handler($this, 'preAction', [$this, 'preAction']);
$this->signal->handler($this, 'postAction', [$this, 'postAction']);
}
public function action()
{
$this->signal->send($this, 'preAction');
$this->doSomething( __METHOD__ );
$this->signal->send($this, 'postAction');
}
public function preAction()
{
// happens before the main action() logic
}
public function postAction()
{
// happens after the main action() logic
}
}
When ExampleAnotherChild::action()
is called, the code:
-
Sends a
'preAction'
signal to theManager
, which in turn calls thepreAction()
method on the object -
Calls the
doSomething()
method on the object (n.b., remember that thedoSomething()
method sends an'example_signal'
of its own to theManager
) -
Sends a
'postAction'
signal to theManager
, which in turn calls thepostAction()
method on the object.
If there are class-based handlers for ExampleAnotherChild
class or its parents, those will also be executed. This means we can set up combinations of handlers to be applied to classes overall, along with handlers that are tied to specific objects.
Advanced Usage
Handler Position Groups
By default, all Handler
objects will be appended to the Manager
stack, and will be processed the order they were added. Sometimes you will need a Handler
to be processed in a different order; for example, before or after all others. If so, you can pass a $position
value when adding a Handler
to the Manager
. (The default $position
for Handler
objects is 5000.)
<?php
// add a closure at position 1000, which means it will be processed
// before all handlers at the default position 5000.
$closure = function() {
echo "Before all others.";
return "First closure";
};
$signal->handler('Vendor\Package\ExampleChild', 'example_signal', $closure, 1000);
// add a closure at position 9000, which means it will be processed
// after all handlers at the default position 5000.
$closure = function() {
echo "After all others.";
return "Second closure";
};
$signal->handler('Vendor\Package\ExampleChild', 'example_signal', $closure, 1000);
Handler
objects added at a position will still be appended within that position group.
Result Inspection
After a signal has been sent, we can review the results returned by every handler for that signal.
<?php
// send a signal
$this->signal->send($this, 'example_signal');
// get the result collection
$results = $this->signal->getResults();
// go through each result ...
foreach ($results as $result) {
// ... and echo the value returned by the Handler callback
echo $result->value;
}
The getResults()
method returns a ResultCollection
of Result
objects, each of which has these properties:
-
$origin
: The object that sent the signal. -
$sender
: The sender expected by theHandler
. -
$signal
: The signal that was sent by the origin. -
$value
: The value returned by theHandler
callback.
If you need only the last result, you can call getLast()
on the ResultCollection
object.
<?php
// send a signal and retain the results from each Handler
$results = $this->signal->send($this, 'example_signal');
// get the last result
$result = $results->getLast();
// and echo the value returned by the last Handler callback
echo $result->value;
Stopping Signal Processing
Sometimes it will be necessary to stop processing signal handlers. If a handler callback returns the aura\signal\Manager::STOP
constant, then no more handlers for that signal will be processed.
First we define the handlers; note that the second one returns the STOP
constant:
<?php
// add signal handlers
$signal->handler(
'Vendor\Package\Example',
'mock_signal',
function() { return 'first'; }
);
$signal->handler(
'Vendor\Package\Example',
'mock_signal',
function() { return \Aura\Signal\Manager::STOP; }
);
$signal->handler(
'Vendor\Package\Example',
'mock_signal',
function() { return 'third'; }
);
Then, from inside an object, we send a signal:
<?php
$results = $this->signal->send($this, 'mock_signal');
// Or you can get via
// $results = $this->signal->getResults();
Normally, $results
would have three entries. In this case it has only two, because the second handler returned \aura\signal\Manager::STOP
. As such, the third handler was never executed. You can call ResultCollection::isStopped()
to see if the Manager
stopped processing handlers in this way.
<?php
if ($results->isStopped()) {
$result = $results->getLast();
echo "Processing for signal 'mock_signal' stopped "
. "by handler for " . $result->sender;
}
Setting Handlers at Construction
It is possible to set the Handler
definitions for a Manager
at construction time. This allows us to use one or more config files to define the Handler
stack for a Manager
.
Given this file at /path/to/signal_handlers.php
...
<?php
return [
// first handler, with a closure
[
'Vendor\Package\Example',
'mock_signal',
function() { return 'foo'; },
],
// second handler, with a static callback
[
'Vendor\Package\Example',
'mock_signal',
['Vendor\Package\SomeClass', 'someMethod'],
],
// third handler, with a closure and position
[
'Vendor\Package\Example',
'mock_signal',
function() { return 'baz'; },
1000,
],
];
... we can configure a Manager
like so:
<?php
namespace Aura\Signal;
$handlers = require '/path/to/signal_handlers.php';
$signal = new Manager(
new HandlerFactory,
new ResultFactory,
new ResultCollection,
$handlers
);
That is the equivalent of calling $signal->handler()
three times to add each handler.
Thanks
Thanks to Richard "Cyberlot" Thomas for the original suggestion, Galactic Void for bringing it back up, and Matthew Weier O'Phinney.