Introduction
One of the real challenges in building any type of framework, core or application is making it possible for the developers to hook into the business logic at specific points. Since PHP is not event based, nor it works with interrupts you have to come up an alternative.
The test case
Lets assume we are the main developers of a webshop framework. Programmers can use our framework to build complete webshops. Programmers can manage the orders that are placed on the webshop with the order class. The order class is part of our framework and we don’t want it to be extended by any programmer. However we don’t want to limit to programmers in their possibilities to hook into the orders process.
For example programmers should be able to send an email to the webshopowner if an order changes from one specific delivery status to another. This functionality is not part of the default behavior in our framework and is custom for the progammers webshop implementation.
Like said before, PHP doesn’t provide interrupts or real events so we need to come up with another way to implement hooks into our application. Lets take a look at the observer pattern.
Implementing the Observer pattern
The observer pattern is a design-pattern that describes a way for objects to be notified to specific state-changes in objects of the application.
For the first implementation we can use SPL. The SPL provides in two simple objects:
SPLSubject
- attach (new observer to attach)
- detach (existing observer to detach)
- notify (notify all observers)
SPLObserver
- update (Called from the subject (i.e. when it’s value has changed).
iOrderRef = $iOrderRef;
// Get order information from the database or an other resources
$this->iStatus = Order::STATUS_SHIPPED;
}
/**
* Attach an observer
*
* @param SplObserver $oObserver
* @return void
*/
public function attach(SplObserver $oObserver)
{
$sHash = spl_object_hash($oObserver);
if (isset($this->aObservers[$sHash])) {
throw new Exception('Observer is already attached');
}
$this->aObservers[$sHash] = $oObserver;
}
/**
* Detach observer
*
* @param SplObserver $oObserver
* @return void
*/
public function detach(SplObserver $oObserver)
{
$sHash = spl_object_hash($oObserver);
if (!isset($this->aObservers[$sHash])) {
throw new Exception('Observer not attached');
}
unset($this->aObservers[$sHash]);
}
/**
* Notify the attached observers
*
* @param string $sEvent, name of the event
* @param mixed $mData, optional data that is not directly available for the observers
* @return void
*/
public function notify()
{
foreach ($this->aObservers as $oObserver) {
try {
$oObserver->update($this);
} catch(Exception $e) {
}
}
}
/**
* Add an order
*
* @param array $aOrder
* @return void
*/
public function delete()
{
$this->notify();
}
/**
* Return the order reference number
*
* @return int
*/
public function getRef()
{
return $this->iOrderRef;
}
/**
* Return the current order status
*
* @return int
*/
public function getStatus()
{
return $this->iStatus;
}
/**
* Update the order status
*/
public function updateStatus($iStatus)
{
$this->notify();
// ...
$this->iStatus = $iStatus;
// ...
$this->notify();
}
}
/**
* Order status handler, observer that sends an email to secretary
* if the status of an order changes from shipped to delivered, so the
* secratary can make a phone call to our customer to ask for his opinion about the service
*
* @package Shop
*/
class OrderStatusHandler implements SplObserver
{
/**
* Previous orderstatus
* @var int
*/
protected $iPreviousOrderStatus;
/**
* Current orderstatus
* @var int
*/
protected $iCurrentOrderStatus;
/**
* Update, called by the observable object order
*
* @param Observable_Interface $oSubject
* @param string $sEvent
* @param mixed $mData
* @return void
*/
public function update(SplSubject $oSubject)
{
if(!$oSubject instanceof Order) {
return;
}
if(is_null($this->iPreviousOrderStatus)) {
$this->iPreviousOrderStatus = $oSubject->getStatus();
} else {
$this->iCurrentOrderStatus = $oSubject->getStatus();
if($this->iPreviousOrderStatus === Order::STATUS_SHIPPED && $this->iCurrentOrderStatus === Order::STATUS_DELIVERED) {
$sSubject = sprintf('Order number %d is shipped', $oSubject->getRef());
//mail('secratary@example.com', 'Order number %d is shipped', 'Text');
echo 'Mail sended to the secratary to help her remember to call our customer for a survey.';
}
}
}
}
$oOrder = new Order(26012011);
$oOrder->attach(new OrderStatusHandler());
$oOrder->updateStatus(Order::STATUS_DELIVERED);
$oOrder->delete();
?>
There are several problems with the implementation above. To most important disadvantage is that we have only one update method in our observer. In this update method we don’t know when and why we are getting notified, just that something happened. We should keep track of everything that happens in the subject. (Or use debug_backtrace… just joking, don’t even think about using it that way ever!).
Taking it a step further, events
Lets take a look at the next example, we will extend the Observer implementation with some an additional parameter for the eventname that occured.
Finishing up, optional data
iOrderRef = $iOrderRef;
// Get order information from the database or something else...
$this->iStatus = Order::STATUS_SHIPPED;
}
/**
* Attach an observer
*
* @param Observer_Interface $oObserver
* @return void
*/
public function attachObserver(Observer_Interface $oObserver)
{
$sHash = spl_object_hash($oObserver);
if (isset($this->aObservers[$sHash])) {
throw new Exception('Observer is already attached');
}
$this->aObservers[$sHash] = $oObserver;
}
/**
* Detach observer
*
* @param Observer_Interface $oObserver
* @return void
*/
public function detachObserver(Observer_Interface $oObserver)
{
$sHash = spl_object_hash($oObserver);
if (!isset($this->aObservers[$sHash])) {
throw new Exception('Observer not attached');
}
unset($this->aObservers[$sHash]);
}
/**
* Notify the attached observers
*
* @param string $sEvent, name of the event
* @param mixed $mData, optional data that is not directly available for the observers
* @return void
*/
public function notifyObserver($sEvent, $mData=null)
{
foreach ($this->aObservers as $oObserver) {
try {
$oObserver->update($this, $sEvent, $mData);
} catch(Exception $e) {
}
}
}
/**
* Add an order
*
* @param array $aOrder
* @return void
*/
public function add($aOrder = array())
{
$this->notifyObserver('onAdd');
}
/**
* Return the order reference number
*
* @return int
*/
public function getRef()
{
return $this->iOrderRef;
}
/**
* Return the current order status
*
* @return int
*/
public function getStatus()
{
return $this->iStatus;
}
/**
* Update the order status
*/
public function updateStatus($iStatus)
{
$this->notifyObserver('onBeforeUpdateStatus');
// ...
$this->iStatus = $iStatus;
// ...
$this->notifyObserver('onAfterUpdateStatus');
}
}
/**
* Order status handler, observer that sends an email to secretary
* if the status of an order changes from shipped to delivered, so the
* secratary can make a phone call to our customer to ask for his opinion about the service
*
* @package Shop
*/
class OrderStatusHandler implements Observer_Interface
{
protected $iPreviousOrderStatus;
protected $iCurrentOrderStatus;
/**
* Update, called by the observable object order
*
* @param Observable_Interface $oObservable
* @param string $sEvent
* @param mixed $mData
* @return void
*/
public function update(Observable_Interface $oObservable, $sEvent, $mData=null)
{
if(!$oObservable instanceof Order) {
return;
}
switch($sEvent) {
case 'onBeforeUpdateStatus':
$this->iPreviousOrderStatus = $oObservable->getStatus();
return;
case 'onAfterUpdateStatus':
$this->iCurrentOrderStatus = $oObservable->getStatus();
if($this->iPreviousOrderStatus === Order::STATUS_SHIPPED && $this->iCurrentOrderStatus === Order::STATUS_DELIVERED) {
$sSubject = sprintf('Order number %d is shipped', $oObservable->getRef());
//mail('secratary@example.com', 'Order number %d is shipped', 'Text');
echo 'Mail sended to the secratary to help her remember to call our customer for a survey.';
}
}
}
}
$oOrder = new Order(26012011);
$oOrder->attachObserver(new OrderStatusHandler());
$oOrder->updateStatus(Order::STATUS_DELIVERED);
$oOrder->add();
?>
Now we are able to take action on different events that occur.
Disadvantages
Although this implementation works quite well there are some drawbacks. One of those drawbacks is that we need to dispatch an event in our framework, if we don’t programmers can’t hook into our application. Triggering events everywhere give us a small performance penalty however I do think this way of working gives the programmers a nice way to hook into your application on those spots that you want them to hook in.
Just for the record
Notice that this code is just an example and can still use some improvements, for example: each observer is initialized even it will maybe never be notified, therefore I suggest to make use of lazy in some cases for loading the objects. There are other systems to hook into an application, more to follow!
Гороскоп http://www.istoriamashin.ru .
металлические значки металлические пины значки
Календарь стрижек http://www.inforigin.ru .
Easy object for people on this site https://easygrawvf52.com/
Приобрести диплом института по невысокой стоимости возможно, обращаясь к проверенной специализированной компании. Заказать документ ВУЗа вы сможете у нас в столице. orikdok-2v-gorode-mahachkala-5.ru
вавада казино официальный сайт казино Возможность бесплатно скачать приложение Vavada Casino на телефон – это прекрасная возможность всегда иметь под рукой любимые игры. Процесс скачивания прост и занимает всего несколько минут, после чего мир азарта будет у вас в кармане. Vavada Casino Отзывы
Купить диплом института по невысокой цене возможно, обратившись к надежной специализированной фирме. Заказать документ университета можно в нашей компании в Москве. [url=http://orikdok-1v-gorode-kemerovo-42.ru/]orikdok-1v-gorode-kemerovo-42.ru[/url]
мостбет скачать приложение на андроид бесплатно http://mostbet11008.ru/
Hey just wanted to give you a quick heads up.
The words in your content seem to be running off the screen in Safari.
I’m not sure if this is a formatting issue or
something to do with browser compatibility but I figured I’d post to let you know.
The design and style look great though! Hope you get
the issue fixed soon. Many thanks
типография санкт петербург печать спб типография
типография заказать типография дешево
заказать металлические значки металлические значки
“Thanks for breaking this down so clearly! I had no idea how
much gut health impacts overall wellness. Prime Biome sounds like a solid, natural option.”
Hey I know this is off topic but I was wondering if you
knew of any widgets I could add to my blog that automatically tweet my newest twitter updates.
I’ve been looking for a plug-in like this for quite some time and was hoping maybe you would have some experience with something like this.
Please let me know if you run into anything.
I truly enjoy reading your blog and I look forward to your
new updates.
casino online australia http://www.maryvaleqld.com.au .
айфлоу citadel-trade.ru .
new australian casino http://maryvaleqld.com.au/new-online-casinos// .
mostbet casino [url=mostbet11028.ru]mostbet11028.ru[/url]
Когда я увидел этот мир, ощущение было таким, будто я переступил грань реальности. Здесь каждая игра — это не просто волнение, а эмоция, которую ты ощущаешь с каждым кликом.
Интерфейс интуитивен, словно легкое прикосновение направляет тебя от момента к моменту. Транзакции, будь то депозиты или выплаты, проходят быстро, как поток воды, и это вдохновляет. А поддержка всегда готова подхватить, как надежный товарищ, который никогда не разочарует.
Для меня Селектор стал миром, где удовольствие и смысл сплетаются. Здесь каждая минута — это часть истории, которую хочется переживать снова и снова.
типография сайт печать спб типография
типография типография заказать
I love it whenever people get together and share views.
Great website, continue the good work!
мостбет скачать андроид мостбет скачать андроид
типография сайт типография
металлические значки москва металлические значки на заказ
типография сайт типография официальный сайт
заказать металлические значки металлические значки на заказ
Магнитные бури https://topoland.ru .
Календарь стрижек https://www.topoland.ru .
Great information. Lucky me I recently found your blog by accident (stumbleupon).
I’ve book-marked it for later!
Суши роллы
Календарь стрижек http://www.topoland.ru .
Hello it’s me, I am also visiting this website daily, this site is
genuinely good and the visitors are actually sharing pleasant thoughts.
This is very interesting, You are a very skilled blogger.
I have joined your rss feed and look forward to seeking more of your magnificent post.
Also, I have shared your site in my social networks!
mostbet for pc mostbet for pc
быстрая регистрация на мостбет быстрая регистрация на мостбет
magnificent issues altogether, you just received a emblem new reader.
What could you suggest in regards to your put up that you made a few days ago?
Any positive?
ремонт холодильников жетысуский район Дефектовка холодильника Алматы: Выявление всех дефектов и неисправностей.
mostbet aplikace https://www.mostbet11028.ru
mental health support chat http://mental-health5.com/ .
Заказать поке
Very quickly this site will be famous amid all blogging and site-building people, due to it’s pleasant posts
Wassup guys, I’m Marko from Serbia. I wanna tell you about
my insane experience with this new online casino I stumbled
on a few weeks ago.
To be honest, I was living paycheck to paycheck, and now I can’t believe it myself — I scored $1,500,
000 playing mostly sports bets!
Now I’m thinking of buying a boat here in Zagreb, and investing a serious chunk of my winnings into Cardano.
Later I’ll probably move to a better neighborhood and support my family.
Now I’m going by Tomasz from Poland because I honestly feel like a new person. My
life is flipping upside down in the best way.
No cap, what would you guys do if you had this kinda luck?
Are you thinking “damn!” right now?
For real, I never thought I’d get out of debt.
It’s all happening so fast!
Drop your thoughts below!
металлические значки на заказ заказать металлические значки
Бездепозитные бонусы в казино Казино, предлагающие бездепозитные бонусы, словно заботливые хозяева, приглашают гостей в свой дом и предлагают им угощение на пробу. Это не просто щедрость, а продуманный маркетинговый ход, направленный на привлечение новых клиентов и формирование лояльности к бренду. Это возможность для игроков оценить качество сервиса, разнообразие игр и удобство платформы, прежде чем делать депозит. Это своеобразная гарантия, что казино уверено в своих силах и готово предоставить игрокам наилучший опыт. Бездепозитный бонус
мостбет. [url=https://mostbet11014.ru]мостбет.[/url]
займ под залог кредитного авто
zaimpod-pts92.ru/ekb.html
займ под залог птс авто
Great article, just what I was looking for.
I loved as much as you will receive carried out right
here. The sketch is tasteful, your authored subject matter stylish.
nonetheless, you command get bought an nervousness over that you wish be delivering
the following. unwell unquestionably come more formerly again since
exactly the same nearly a lot often inside case you shield this hike.
It is perfect time to make a few plans for the future and it is time to be happy.
I have learn this put up and if I may I want to recommend you few interesting issues or tips.
Maybe you could write subsequent articles
referring to this article. I want to read even more issues approximately it!