The document discusses various programming concepts in Objective-C, focusing on performance comparisons between direct property access and accessors, risks associated with each method, and the use of design patterns like categories and associative storage. It highlights how categories can be employed to add methods to existing classes and manage complexity, while associative storage enables adding new properties to classes without subclassing. Additionally, it provides examples of implementing these patterns through code snippets and emphasizes methods for improving functionality across different OS versions.

1. CocoaHeads
14 Mai 2013
mardi 28 mai 13

2. Backelite...
...recrute !mardi 28 mai 13

3. Au programme
• Accessors Vs Direct access to properties
• Design Pattern : Categories
• Design Pattern : Associative Storage
• La chaine Météo!
mardi 28 mai 13

4. iVar : Accessors/Direct access
• Performance ?
• Risks / Limits ?
mardi 28 mai 13

5. property Using setter (ms)
Using Direct Access
(ms)
strong + nonatomic 9 6
weak + nonatomic 30 30
unsafe_unretained +
nonatomic
0,8 0,2
strong + atomic 9 6
iPhone 3GS/iOS5 + 10,000 affectactions. (average based
on several tests.)
iVar : Accessors/Direct access
Performance?
mardi 28 mai 13

6. • Direct affectation don’t use the property
attributes (atomic)
• KVO/KVC needs accessors,
• Don’t use accessor methods in init methods
and dealloc (You may have override your
accessors)
iVar : Accessors/Direct access
Risk / Limits?
mardi 28 mai 13

7. Design Pattern: Categories
• Add new methods to existing classes
#import "IBSHelper.h"
@interface IBSHelper (FileName)
+ (NSString*)filenameForGeolocData;
+ (NSString*)filenameForBrandCodeData;
+ (NSString*)filenameForTradData;
+ (NSString *)currentLanguage;
+ (NSString *)currentLanguageForDownload;
+ (NSURL*)urlForGeolocData;
+ (NSURL*)urlForBrandData;
+ (NSURL*)urlForTradData;
@end
mardi 28 mai 13

8. Design Pattern: Categories
• Organize/split complexity
mardi 28 mai 13

9. Design Pattern: Categories
• Makes easy to support multiple OS versions
@interface UITableView (BkUICore)
- (void) bkRegisterNibName:(NSString *)nibName forCellReuseIdentifier:
(NSString *)identifier;
- (id) bkDequeueReusableCellWithIdentifier:(NSString *)identifier;
@end
@interface UIViewController (BkUICore)
- (void) bkDismissModalViewControllerAnimated:(BOOL)animated;
- (void) bkPresentViewController:(UIViewController *)controller
animated:(BOOL)animated;
@end
mardi 28 mai 13

10. Design Pattern: Categories
• Categories can be used to declare either instance
methods or class methods but are not usually
suitable for declaring additional properties.
One other design pattern can help us !
Associated storage
@interface UITableView (BkUICore)
- (void) bkRegisterNibName:(NSString *)nibName forCellReuseIdentifier:
(NSString *)identifier;
- (id) bkDequeueReusableCellWithIdentifier:(NSString *)identifier;
@end
mardi 28 mai 13

11. Design Pattern: Associative references
http://developer.apple.com/library/mac/#documentation/
Cocoa/Conceptual/ObjCRuntimeGuide/Introduction/
Introduction.html#//apple_ref/doc/uid/TP40008048
Objective-C programs interact with the runtime system at three distinct
levels: through Objective-C source code; through methods defined in the
NSObject class of the Foundation framework; and through direct calls to
runtime functions.
mardi 28 mai 13

12. Design Pattern: Associative references
//nsobjet.h
@interface NSObject
+ (Class)superclass;
+ (Class)class;
- (BOOL)respondsToSelector:(SEL)aSelector;
+ (BOOL)conformsToProtocol:(Protocol *)protocol;
//runtime.h
OBJC_EXPORT Class class_getSuperclass(Class cls)
OBJC_EXPORT Class object_getClass(id obj)
OBJC_EXPORT BOOL class_respondsToSelector(Class cls, SEL sel)
OBJC_EXPORT BOOL class_conformsToProtocol(Class cls, Protocol *protocol)
Some of the NSObject methods simply query the runtime system for information.
These methods allow objects to perform introspection.
mardi 28 mai 13

13. • A way to add simulate new properties to an
existing class !
Design Pattern: Associative references
static const char nibsAssocKey;
@implementation UITableView (BkUICore)
- (void) bkRegisterNibName:(NSString *)nibName forCellReuseIdentifier:(NSString
*)identifier
{
if ([self respondsToSelector:@selector(registerNib:forCellReuseIdentifier:)]) {
[self registerNib:[UINib nibWithNibName:nibName bundle:[NSBundle mainBundle]]
forCellReuseIdentifier:identifier]; //NS_AVAILABLE_IOS(5_0)
} else {
NSMutableDictionary *nibs = objc_getAssociatedObject(self, &nibsAssocKey);
if (nil == nibs) {
nibs = [NSMutableDictionary dictionary];
objc_setAssociatedObject(self, &nibsAssocKey,
nibs, OBJC_ASSOCIATION_RETAIN);
}
[nibs setValue:nibName forKey:identifier];
}
}
@end
mardi 28 mai 13

14. La chaine meteo
Issue : How to add a new property on UINavigationBar
• Subclass UINavigationBar, dumbass !
• Use associated storage !
mardi 28 mai 13

15. La chaine meteo
mardi 28 mai 13

16. Other examples
• UIView + BkBadge
• UIView + BkLoader
....
mardi 28 mai 13

17. Thanks
mardi 28 mai 13