Objective C Runtime

Learn the runtime that powers our app

Transcript

1. Objective C Runtime Khoa Pham 2359Media
2. Today • self = [super init] • objc_msgSend • ObjC Runtime • How to use the Runtime API • Use cases
3. self = [super init] ETPAnimal *cat = [ETPAnimal cat]; NSInteger recordCount = [ETPCoreDataManager recordCount];
4. self = [super init] @interface ETPCat : ETPAnimal @end ETPCat *cat = [[ETPCat alloc] init]
5. self = [super init] - (id)init { self = [super init]; if (self) { // ETPCat does it own initialization here } return self; }
6. self = [super init] [super init] calls the superclass implementation of init with the (hidden) self argument. It can do one of these things + set some properties on self, and return self + return a different object (factory, singleton) + return nil
7. self = [super init] ETPCat *cat = [ETPCat alloc] // 0x1111111a [cat init] // 0x1111111b [cat meomeo] // 0x1111111a
8. self = [super init] Demo
9. objc_msgSend ETPCat *cat = [[ETPCat alloc] init] [cat setName:@”meo”] objc_msgSend(cat, @selector(setName:), @”meo”)
10. objc_msgSend Demo
11. objc_msgSend
12. @selector SEL selector1 = @selector(initWithName:) SEL selector2 = @selector(initWithFriends1Name::) typedef struct objc_selector *SEL Read more at Objective C Runtime Reference -> Data Structure -> Class definition Data structure -> SEL
13. @selector Demo
14. Objective C Runtime The Objective-C Runtime is a Runtime Library, it's a library written mainly in C & Assembler that adds the Object Oriented capabilities to C to create Objective-C.
15. Objective C Runtime Source code http://www.opensource.apple. com/source/objc4/objc4-532/runtime/objc-class.mm There are two versions of the Objective-C runtime— “modern” and “legacy”. The modern version was introduced with Objective-C 2.0 and includes a number of new features.
16. Objective C Runtime Dynamic feature Object oriented capability
17. Objective C Runtime Features • Class elements (categories, methods, variables, property, …) • Object • Messaging • Object introspection
18. Objective C Runtime @interface ETPAnimal : NSObject @end typedef struct objc_class *Class;
19. Objective C Runtime (old) struct objc_class { Class isa; Class super_class OBJC2_UNAVAILABLE; const char *name OBJC2_UNAVAILABLE; long version OBJC2_UNAVAILABLE; long info OBJC2_UNAVAILABLE; long instance_size OBJC2_UNAVAILABLE; struct objc_ivar_list *ivars OBJC2_UNAVAILABLE; struct objc_method_list **methodLists OBJC2_UNAVAILABLE; struct objc_cache *cache OBJC2_UNAVAILABLE; struct objc_protocol_list *protocols OBJC2_UNAVAILABLE; }
20. Objective C Runtime typedef struct class_ro_t { const char * name; const ivar_list_t * ivars; } class_ro_t typedef struct class_rw_t { const class_ro_t *ro; method_list_t **methods; struct class_t *firstSubclass; struct class_t *nextSiblingClass; } class_rw_t;
21. Objective C Runtime ETPAnimal *animal = [[ETPAnimal alloc] init] struct objc_object { Class isa; // variables };
22. Objective C Runtime id someAnimal = [[ETPAnimal alloc] init] typedef struct objc_object { Class isa; } *id;
23. Objective C Runtime Class is also an object, its isa pointer points to its meta class The metaclass is the description of the class object
24. Objective C Runtime
26. Objective C Runtime Demo
27. Objective C Runtime • Dynamic typing • Dynamic binding • Dynamic method resolution • Introspection
28. Objective C Runtime Dynamic typing Dynamic typing enables the runtime to determine the type of an object at runtime id cat = [[ETPCat alloc] init] - (void)acceptAnything:(id)anything;
29. Objective C Runtime Dynamic binding Dynamic binding is the process of mapping a message to a method at runtime, rather than at compile time
30. Objective C Runtime Dynamic method resolution Provide the implementation of a method dynamically. @dynamic
31. Objective C Runtime Introspection isKindOfClass respondsToSelector conformsToProtocol
32. How to use the Runtime API Objective-C programs interact with the runtime system to implement the dynamic features of the language. • Objective-C source code • Foundation Framework NSObject methods • Runtime library API
33. Use cases Method swizzle (IIViewDeckController) JSON Model (Torin ‘s BaseModel) Message forwarding Meta programming
34. Use cases Method swizzle
35. Use cases Method swizzle (IIViewDeckController) SEL presentVC = @selector(presentViewController:animated:completion:); SEL vdcPresentVC = @selector(vdc_presentViewController:animated:completion:); method_exchangeImplementations(class_getInstanceMethod(self, presentVC), class_getInstanceMethod(self, vdcPresentVC));
36. Use cases Method swizzle (IIViewDeckController) - (void)vdc_presentViewController:(UIViewController *)viewControllerToPresent animated:(BOOL) animated completion:(void (^)(void))completion { UIViewController* controller = self.viewDeckController ?: self; [controller vdc_presentViewController:viewControllerToPresent animated:animated completion: completion]; // when we get here, the vdc_ method is actually the old, real method }
37. Use cases JSON Model (Torin ‘s BaseModel) updateWithDictionary class_copyIvarList ivar_getName
38. Use cases JSON Model (Torin ‘s BaseModel) @interface ETPItem : BaseModel @property (nonatomic, copy) NSString * ID; @property (nonatomic, copy) NSString *name; @end ETPItem *item = [[ETPItem alloc] init]; [item updateWithDictionary:@{@”ID”: @”1”, @”name”: @”item1”}];
39. Message forwarding
40. Use cases Meta programming • Dynamic method naming • Validation • Template • Mocking
41. Reference 1. http://cocoasamurai.blogspot.com/2010/01/understanding-objective-c-runtime.html 2. http://www.slideshare.net/mudphone/what-makes-objective-c-dynamic 3. http://www.cocoawithlove.com/2009/04/what-does-it-mean-when-you-assign-super.html 4. http://nshipster.com/method-swizzling/ 5. http://stackoverflow.com/questions/415452/object-orientation-in-c 6. http://stackoverflow.com/questions/2766233/what-is-the-c-runtime-library 7. http://gcc.gnu.org/onlinedocs/gcc/Modern-GNU-Objective-C-runtime-API.html 8. http://www.opensource.apple.com/source/objc4/objc4-532/runtime/objc-class.mm 9. http://www.friday.com/bbum/2009/12/18/objc_msgsend-part-1-the-road-map/ 10. https://www.mikeash.com/pyblog/friday-qa-2010-01-29-method-replacement-for-fun-and-profit.html 11. Pro Objective C, chapter 7, 8, 9 12. Effective Objective C, chapter 2 13. http://wiki.gnustep.org/index.php/ObjC2_FAQ
42. Thank you Q&A