3.7. Observer¶
3.7.1. Purpose¶
To implement a publish/subscribe behaviour to an object, whenever a “Subject” object changes it’s state, the attached “Observers” will be notified. It is used to shorten the amount of coupled objects and uses loose coupling instead.
3.7.2. Examples¶
- a message queue system is observed to show the progress of a job in a GUI
3.7.3. Note¶
PHP already defines two interfaces that can help to implement this pattern: SplObserver and SplSubject.
3.7.4. UML Diagram¶
3.7.5. Code¶
You can also find these code on GitHub
User.php
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namespace DesignPatterns\Behavioral\Observer;
/**
* Observer pattern : The observed object (the subject)
*
* The subject maintains a list of Observers and sends notifications.
*
*/
class User implements \SplSubject
{
/**
* user data
*
* @var array
*/
protected $data = array();
/**
* observers
*
* @var \SplObjectStorage
*/
protected $observers;
public function __construct()
{
$this->observers = new \SplObjectStorage();
}
/**
* attach a new observer
*
* @param \SplObserver $observer
*
* @return void
*/
public function attach(\SplObserver $observer)
{
$this->observers->attach($observer);
}
/**
* detach an observer
*
* @param \SplObserver $observer
*
* @return void
*/
public function detach(\SplObserver $observer)
{
$this->observers->detach($observer);
}
/**
* notify observers
*
* @return void
*/
public function notify()
{
/** @var \SplObserver $observer */
foreach ($this->observers as $observer) {
$observer->update($this);
}
}
/**
* Ideally one would better write setter/getter for all valid attributes and only call notify()
* on attributes that matter when changed
*
* @param string $name
* @param mixed $value
*
* @return void
*/
public function __set($name, $value)
{
$this->data[$name] = $value;
// notify the observers, that user has been updated
$this->notify();
}
}
|
UserObserver.php
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 | <?php
namespace DesignPatterns\Behavioral\Observer;
/**
* class UserObserver
*/
class UserObserver implements \SplObserver
{
/**
* This is the only method to implement as an observer.
* It is called by the Subject (usually by SplSubject::notify() )
*
* @param \SplSubject $subject
*/
public function update(\SplSubject $subject)
{
echo get_class($subject) . ' has been updated';
}
}
|
3.7.6. Test¶
Tests/ObserverTest.php
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namespace DesignPatterns\Behavioral\Observer\Tests;
use DesignPatterns\Behavioral\Observer\UserObserver;
use DesignPatterns\Behavioral\Observer\User;
/**
* ObserverTest tests the Observer pattern
*/
class ObserverTest extends \PHPUnit_Framework_TestCase
{
protected $observer;
protected function setUp()
{
$this->observer = new UserObserver();
}
/**
* Tests the notification
*/
public function testNotify()
{
$this->expectOutputString('DesignPatterns\Behavioral\Observer\User has been updated');
$subject = new User();
$subject->attach($this->observer);
$subject->property = 123;
}
/**
* Tests the subscribing
*/
public function testAttachDetach()
{
$subject = new User();
$reflection = new \ReflectionProperty($subject, 'observers');
$reflection->setAccessible(true);
/** @var \SplObjectStorage $observers */
$observers = $reflection->getValue($subject);
$this->assertInstanceOf('SplObjectStorage', $observers);
$this->assertFalse($observers->contains($this->observer));
$subject->attach($this->observer);
$this->assertTrue($observers->contains($this->observer));
$subject->detach($this->observer);
$this->assertFalse($observers->contains($this->observer));
}
/**
* Tests the update() invocation on a mockup
*/
public function testUpdateCalling()
{
$subject = new User();
$observer = $this->getMock('SplObserver');
$subject->attach($observer);
$observer->expects($this->once())
->method('update')
->with($subject);
$subject->notify();
}
}
|