The document discusses using events in Symfony applications to decouple classes and increase flexibility, describing how to connect events to listeners, dispatch events, and pass data, as well as some potential issues like lack of notification ordering and increased debugging complexity with events. Examples are provided of using events for actions on state changes, file system operations, and loose coupling of Symfony plugins.

1. Using symfony events to create clean
class interfaces
by Dennis Benkert

2. Dennis Who?!
2

3. Dennis Who?!
2

4. Dennis Who?!
2

5. Dennis Who?!
2

6. Dennis Who?!
2

7. Agenda
3

8. Agenda
Code Coupling
3

9. Agenda
Code Coupling
Event Basics
3

10. Agenda
Code Coupling
Event Basics
Events in Code
3

11. Agenda
Code Coupling
Event Basics
Events in Code
Usage Examples
3

12. Agenda
Code Coupling
Event Basics
Events in Code
Usage Examples
Problems of Events
3

13. Code Coupling
4

14. In the beginning it‘s all so cleaned up...
... but over time things start to change
5

15. „Coupling is the single greatest problem in large
software systems“
- Ted Faison
6

16. „You don‘t want to achieve consistency by making the
classes tightly coupled, because that reduces their
reuseability“
- Gang of Four
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17. Separation of Concerns
8

18. Separation of Concerns
8

19. Separation of Concerns
8

20. Separation of Concerns
8

21. Separation of Concerns
8

22. Separation of Concerns
8

23. Separation of Concerns
8

24. Separation of Concerns
8

25. Separation of Concerns
8

26. Separation of Concerns
Events, DI, ...
8

27. Event Basics
9

28. Event Connection
Event Dispatcher
Software Components
10

29. Event Connection
Event Dispatcher
Software Components
10

30. Event Connection
Event Dispatcher
connect
(registration.complete) .
Software Components
10

31. Event Connection
Event Dispatcher
connect
(registration.complete) .
Software Components
10

32. Event Connection
Event Dispatcher
connect
connect (registration.complete)
(registration.complete) .
Software Components
10

33. Basic Event Notification
11

34. Basic Event Notification
11

35. Basic Event Notification
notify
11

36. Basic Event Notification
notify
(registration.complete)
11

37. Basic Event Notification
notify
(registration.complete)
11

38. Basic Event Notification
notify
(registration.complete)
notification
11

39. Basic Event Notification
notify
(registration.complete)
notification
11

40. Basic Event Notification
notify
(registration.complete)
notification
11

41. Basic Event Notification
notify
(registration.complete)
notification
notification
11

42. Basic Event Notification
notify
(registration.complete)
notification
notification
11

43. More Event Notifications
12

44. More Event Notifications
12

45. More Event Notifications
filter
12

46. More Event Notifications
filter
(blog_post.render)
12

47. More Event Notifications
filter
(blog_post.render)
12

48. More Event Notifications
filter
(blog_post.render)
notification
12

49. More Event Notifications
filter
(blog_post.render)
notification
12

50. More Event Notifications
filter
(blog_post.render)
notification
12

51. More Event Notifications
filter
(blog_post.render)
returnValue
notification
12

52. More Event Notifications
filter
(blog_post.render)
returnValue
notification
12

53. More Event Notifications
filter
(blog_post.render)
returnValue notification
notification
12

54. More Event Notifications
filter
(blog_post.render)
returnValue notification
notification
12

55. More Event Notifications
filter
(blog_post.render)
returnValue notification
notification
12

56. More Event Notifications
filter
(blog_post.render)
returnValue
returnValue notification
notification
12

57. More Event Notifications
filter
(blog_post.render)
returnValue
returnValue notification
notification
12

58. More Event Notifications
returnValue
filter
(blog_post.render)
returnValue
returnValue notification
notification
12

59. More Event Notifications
13

60. More Event Notifications
13

61. More Event Notifications
notifyUntil
13

62. More Event Notifications
notifyUntil
(registration.complete)
13

63. More Event Notifications
notifyUntil
(registration.complete)
13

64. More Event Notifications
notifyUntil
(registration.complete)
notification
13

65. More Event Notifications
notifyUntil
(registration.complete)
notification
13

66. More Event Notifications
notifyUntil
(registration.complete)
notification
13

67. More Event Notifications
notifyUntil
(registration.complete)
returnValue
notification
13

68. More Event Notifications
notifyUntil
(registration.complete)
returnValue
notification
13

69. More Event Notifications
returnValue
notifyUntil
(registration.complete)
returnValue
notification
13

70. More Event Notifications
returnValue
notifyUntil
(registration.complete)
returnValue
notification
13

71. More Event Notifications
returnValue
notifyUntil
(registration.complete)
returnValue
notification
13

72. More Event Notifications
returnValue
notifyUntil
(registration.complete)
returnValue
notification
13

73. More Event Notifications
returnValue
notifyUntil
(registration.complete)
returnValue
notification
13

74. Events in Code
14

75. Events in Code
class frontendConfiguration extends sfApplicationConfiguration
{
public function configure()
{
$this->dispatcher->connect('registration.complete',
array(SomeClass, 'listenToRegistrationComplete'));
// [...]
}
}
15

76. Events in Code
class frontendConfiguration extends sfApplicationConfiguration
{
public function configure()
{
$this->dispatcher->connect('registration.complete',
array(SomeClass, 'listenToRegistrationComplete'));
// [...]
}
}
15

77. Events in Code
Event Name
class frontendConfiguration extends sfApplicationConfiguration
{
public function configure()
{
$this->dispatcher->connect('registration.complete',
array(SomeClass, 'listenToRegistrationComplete'));
// [...]
}
}
15

78. Events in Code
Event Name
class frontendConfiguration extends sfApplicationConfiguration
{
public function configure()
{
$this->dispatcher->connect('registration.complete',
array(SomeClass, 'listenToRegistrationComplete'));
// [...]
}
}
15

79. Events in Code
Event Name
class frontendConfiguration extends sfApplicationConfiguration
{
public function configure()
{
$this->dispatcher->connect('registration.complete',
array(SomeClass, 'listenToRegistrationComplete'));
// [...]
}
}
Callable
(can be static or non-static)
15

80. Events in Code
$this->dispatcher->notify(new sfEvent($user, 'registration.complete'));
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81. Events in Code
$this->dispatcher->notify(new sfEvent($user, 'registration.complete'));
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82. Events in Code
Notification Type
$this->dispatcher->notify(new sfEvent($user, 'registration.complete'));
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83. Events in Code
Notification Type
$this->dispatcher->notify(new sfEvent($user, 'registration.complete'));
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84. Events in Code
Notification Type
$this->dispatcher->notify(new sfEvent($user, 'registration.complete'));
Subject
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85. Events in Code
Notification Type
$this->dispatcher->notify(new sfEvent($user, 'registration.complete'));
Subject
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86. Events in Code
Event Name
Notification Type
$this->dispatcher->notify(new sfEvent($user, 'registration.complete'));
Subject
16

87. Events in Code
class SomeClass
{
public static function listenToRegistrationComplete(sfEvent $event)
{
$user = $event->getSubject();
// [...]
}
}
17

88. Events in Code
class SomeClass
{
public static function listenToRegistrationComplete(sfEvent $event)
{
$user = $event->getSubject();
// [...]
}
}
17

89. Events in Code
Registered Method
(called via notfiy)
class SomeClass
{
public static function listenToRegistrationComplete(sfEvent $event)
{
$user = $event->getSubject();
// [...]
}
}
17

90. Events in Code
Registered Method
(called via notfiy)
class SomeClass
{
public static function listenToRegistrationComplete(sfEvent $event)
{
$user = $event->getSubject();
// [...]
}
}
17

91. Events in Code
Registered Method
(called via notfiy)
class SomeClass
{
public static function listenToRegistrationComplete(sfEvent $event)
{
$user = $event->getSubject();
// [...]
}
}
Event as Parameter
17

92. Events in Code
Registered Method
(called via notfiy)
class SomeClass
{
public static function listenToRegistrationComplete(sfEvent $event)
{
$user = $event->getSubject();
// [...]
}
}
Event as Parameter
17

93. Events in Code
Registered Method
(called via notfiy)
class SomeClass
{
public static function listenToRegistrationComplete(sfEvent $event)
{
$user = $event->getSubject();
// [...]
}
}
Passed Subject
Event as Parameter
17

94. Events in Code
$returnValue = $this->dispatcher->filter(new sfEvent($blogPost,
'blog_post.render'), $blogPost->getBody());
18

95. Events in Code
$returnValue = $this->dispatcher->filter(new sfEvent($blogPost,
'blog_post.render'), $blogPost->getBody());
18

96. Events in Code
Notification Type
$returnValue = $this->dispatcher->filter(new sfEvent($blogPost,
'blog_post.render'), $blogPost->getBody());
18

97. Events in Code
Notification Type
$returnValue = $this->dispatcher->filter(new sfEvent($blogPost,
'blog_post.render'), $blogPost->getBody());
18

98. Events in Code
Notification Type
$returnValue = $this->dispatcher->filter(new sfEvent($blogPost,
'blog_post.render'), $blogPost->getBody());
Raw Value
18

99. Events in Code
Notification Type
$returnValue = $this->dispatcher->filter(new sfEvent($blogPost,
'blog_post.render'), $blogPost->getBody());
Raw Value
18

100. Events in Code
Notification Type
$returnValue = $this->dispatcher->filter(new sfEvent($blogPost,
'blog_post.render'), $blogPost->getBody());
Filtered Value
Raw Value
18

101. Events in Code
class MarkdownParser
{
// [...]
public static function listenToRegistrationComplete(sfEvent $event, $body)
{
$markdownParser = new self();
$parsedBody = $markdownParser->parse($body);
// [...]
return $parsedBody;
}
}
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102. Events in Code
class MarkdownParser
{
// [...]
public static function listenToRegistrationComplete(sfEvent $event, $body)
{
$markdownParser = new self();
$parsedBody = $markdownParser->parse($body);
// [...]
return $parsedBody;
}
}
19

103. Events in Code
Raw Value as Parameter
class MarkdownParser
{
// [...]
public static function listenToRegistrationComplete(sfEvent $event, $body)
{
$markdownParser = new self();
$parsedBody = $markdownParser->parse($body);
// [...]
return $parsedBody;
}
}
19

104. Events in Code
Raw Value as Parameter
class MarkdownParser
{
// [...]
public static function listenToRegistrationComplete(sfEvent $event, $body)
{
$markdownParser = new self();
$parsedBody = $markdownParser->parse($body);
// [...]
return $parsedBody;
}
}
19

105. Events in Code
Raw Value as Parameter
class MarkdownParser
{
// [...]
public static function listenToRegistrationComplete(sfEvent $event, $body)
{
$markdownParser = new self();
$parsedBody = $markdownParser->parse($body);
// [...]
return $parsedBody;
}
}
Filtered Value
19

106. Usage Examples
20

107. Other Usage Examples
skoop
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108. Other Usage Examples
Being able to add extra actions to
specific functionality without having
to alter the existing code.
skoop
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109. Other Usage Examples
snzapka
22

110. Other Usage Examples
I use events mostly with object
states changes, for example to send
email, notify someone, clear cache,
calculate sth.
snzapka
22

111. Other Usage Examples
b00giZm
23

112. Other Usage Examples
I have a centralized "spot" for file
system operations. e.g. when a user
deletes an image from the DB, it
kicks off an event
b00giZm
23

113. Other Usage Examples
helasliban
24

114. Other Usage Examples
Right now I'm using symfony events
for loose coupling of symfony
plugins.
helasliban
24

115. Other Usage Examples
ubermuda
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116. Other Usage Examples
Obfuscate code, totally screwing up
the app's workflow with chain-
binded useless events. o/
ubermuda
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117. Problems of Events
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118. Problems of Events
No Silver Bullet
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119. Problems of Events
No Silver Bullet
Events won‘t help with every problem!
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120. Problems of Events
Use Events for optional coupling
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121. Problems of Events
Use Events for optional coupling
If you need mandatory coupling use DI.
28

122. Problems of Events
No Notification Order
29

123. Problems of Events
No Notification Order
If your listeners need ordering ure doin it rong!
29

124. Problems of Events
Harder debugging
30

125. Problems of Events
Harder debugging
It can get complicated if you do weird things.
30

126. Problems of Events
Harder debugging
It can get complicated if you do weird things.
(Remember ubermuda)
30

127. Problems of Events
Real Setup Hardly Testable
31

128. Problems of Events
Real Setup Hardly Testable
You can never know who connected to an event.
31

129. Problems of Events
Slowness
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130. Problems of Events
Slowness
Every firing starts the Events notification chain.
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131. Thank you!
Give feedback on joind.in, please
http://joind.in/talk/view/1415
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132. Credits
Thanks to:
- Bernhard and Andreas for the reviews and tips.
- Konrad and Samim for the designs and the artworks.
Creative Commons stuff used:
- „Cog, Gear, Settings“ icon by „Visual Pharm“ - http://www.iconfinder.net/icondetails/27879/128/
- „Crying, Man“ icon by Rokey - http://www.iconfinder.net/icondetails/37613/128/
- „Box, Package“ icon by Alessandro Rei - http://www.iconfinder.net/icondetails/6507/128/
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