The document outlines various approaches and issues in Objective-C programming, specifically focusing on the use of categories, associated references, and blocks. It presents examples of the AVAudioPlayer class and discusses the need for new instance variables and language features to enhance functionality. The author emphasizes the importance of these programming concepts, although no definitive conclusions are drawn.

1. THREE
OBJECTIONABLE
THINGS
PETE GOODLIFFE ACCU 2011, Oxford, UK

2. @petegoodliffe
pete@goodliffe.net
goodliffe.blogspot.com
www.goodliffe.net
PETE
PROG
GOOD LIFFE
RAMMER / AUTHOR / C OLUMNIST / TEACHER CO NSCIENTIOUS CODER

5. 3

6. why?

7. GOODLIFFE // PAY ATTENTION!
15 minutes!

8. ASPIDISTRA #1

10. ✔ Play theme tune
(AVAudioPlayer)
✘ Fade in/out

11. Objective-C

12. Objective-C
categories
associative references
blocks

13. ROMAN TRAVELOGUE#2

14. PROBLEM#1
a nice API

15. categories
(because one interface is never enough)

16. AVAudioPlayer *player = … ;
[player play];
[player stop];

17. AVAudioPlayer *player = … ;
[player play];
[player stop];
[player playWithFadeDuration:1.0];
[player stopWithFadeDuration:1.0];

18. @interface AVAudioPlayer
{
…
}
- (id) initWithContentsOfURL:(NSURL*)url;
- (void) play;
- (void) stop;
@end

19. @interface AVAudioPlayer
{
…
}
- (id) initWithContentsOfURL:(NSURL*)url;
- (void) play;
- (void) stop;
- (void) playWithFadeDuration:(float)secs;
- (void) stopWithFadeDuration:(float)secs;
@end

20. @interface AVAudioPlayer (Fades)
- (void) playWithFadeDuration:(float)secs;
- (void) stopWithFadeDuration:(float)secs;
@end

21. @implementation AVAudioPlayer (Fades)
- (void) playWithFadeDuration:(float)secs
{
// magic happens here
}
- (void) stopWithFadeDuration:(float)secs
{
// clever stuff in here
}
@end

22. AVAudioPlayer *player = … ;
[player play];
[player stop];
[player playWithFadeDuration:1.0];
[player stopWithFadeDuration:1.0];
✔

23. THIS IS NOT A
SUBLIMINAL
MESSAGE

24. EQUIDISTANT CAMOMILE#4

25. PROBLEM#2
we need some new
instance variables

26. associative references
(a posh name for cheating)

27. static const char volumeLevelKey = ‘Q’;
NSNumber number = [NSNumber numberWithFloat:1.0];
objc_setAssociatedObject(self,
&volumeLevelKey,
&variable,
OBJ_ASSOCIATION_RETAIN_NONATOMIC);

28. NSNumber *number =
(NSNumber*)objc_getAssociatedObject(self, &volumeLevelKey);

29. @interface AVAudioPlayer (Fades)
- (void) playWithFadeDuration:(float)secs;
- (void) stopWithFadeDuration:(float)secs;
@property float fadeVolume;
@end

30. - (void) fadeVolume
{
// gibberish in here
}
- (void) setFadeVolume
{
// cobblers in here
}
✔
float fadeVolume = player.fadeVolume;

31. A TRAVESTY OF PYLON#6

32. PROBLEM#3
we need to use another
fancy language feature

33. blocks
(because C++ isn’t the only cool language)

34. PROBLEM#3
when a fade has
completed, do
“something”

35. typedef void (^FadeCompleteBlock)();

36. typedef void (^FadeCompleteBlock)();
- (void) fadeToVolume:(float)volume
withDuration:(float)secs
andThen:(FadeCompleteBlock)action

37. typedef void (^FadeCompleteBlock)();
- (void) fadeToVolume:(float)volume
withDuration:(float)secs
andThen:(FadeCompleteBlock)action
[player fadeToVolume:0.0
withDuration:1.0
andThen:^{
[player stop];
player.volume = 1.0;
}];

38. TRANSCENDENTAL SHOE #7

39. the morale of the story
(there is none)

40. QA &
Pete Goodliffe @petegoodliffe pete@goodliffe.net

41. @petegoodliffe
pete@goodliffe.net
goodliffe.blogspot.com
www.goodliffe.net

42. i knew you’d want another
[UIView animateWithDuration:0.5
animations:^{
imageView.layer.opacity = 0.1;
}
completion:^(BOOL finished){
[imageView removeFromSuperview];
}

43. BUMPH DULL, but important
THIS DOCUMENT WAS CREATED BY PETE GOODLIFFE
IT IS COPYRIGHT // © 2011 PETE GOODLIFFE
>> ALL RIGHTS RESERVED
>> ALL THOUGHTS ARE OWNED
>> PHOTOS AND IMAGES ARE MOSTLY
SOURCED FROM THE WEB
THANK YOU FOR READING // I HOPE IT WAS USEFUL
Version 1.0 2011-04-04