My lightning keynote talk at the ACCU 2011 software development conference. This talks about three Objective C language features and how they came together to solve a problem in a "simple" and "elegant" way.

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