Objective C Runtime

Learn the runtime that powers our app

Transcript

1. Objective C Runtime
   Khoa Pham
   2359Media
   

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2. Today
   ● self = [super init]
   ● objc_msgSend
   ● ObjC Runtime
   ● How to use the Runtime API
   ● Use cases
   

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3. self = [super init]
   ETPAnimal *cat = [ETPAnimal cat];
   NSInteger recordCount = [ETPCoreDataManager
   recordCount];
   

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4. self = [super init]
   @interface ETPCat : ETPAnimal
   @end
   ETPCat *cat = [[ETPCat alloc] init]
   

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5. self = [super init]
   - (id)init
   {
   self = [super init];
   if (self) {
   // ETPCat does it own initialization here
   }
   return self;
   }
   

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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
   

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7. self = [super init]
   ETPCat *cat = [ETPCat alloc] // 0x1111111a
   [cat init] // 0x1111111b
   [cat meomeo] // 0x1111111a
   

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8. self = [super init]
   Demo
   

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9. objc_msgSend
   ETPCat *cat = [[ETPCat alloc] init]
   [cat setName:@”meo”]
   objc_msgSend(cat, @selector(setName:), @”meo”)
   

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10. objc_msgSend
    Demo
    

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11. objc_msgSend
    

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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
    

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13. @selector
    Demo
    

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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.
    

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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.
    

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16. Objective C Runtime
    Dynamic feature
    Object oriented capability
    

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17. Objective C Runtime
    Features
    ● Class elements (categories, methods, variables,
    property, …)
    ● Object
    ● Messaging
    ● Object introspection
    

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18. Objective C Runtime
    @interface ETPAnimal : NSObject
    @end
    typedef struct objc_class *Class;
    

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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;
    }
    

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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;
    

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21. Objective C Runtime
    ETPAnimal *animal = [[ETPAnimal alloc] init]
    struct objc_object
    {
    Class isa;
    // variables
    };
    

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22. Objective C Runtime
    id someAnimal = [[ETPAnimal alloc] init]
    typedef struct objc_object
    {
    Class isa;
    } *id;
    

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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
    

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24. Objective C Runtime
    

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26. Objective C Runtime
    Demo
    

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27. Objective C Runtime
    ● Dynamic typing
    ● Dynamic binding
    ● Dynamic method resolution
    ● Introspection
    

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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;
    

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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
    

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30. Objective C Runtime
    Dynamic method resolution
    Provide the implementation of a method dynamically.
    @dynamic
    

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31. Objective C Runtime
    Introspection
    isKindOfClass
    respondsToSelector
    conformsToProtocol
    

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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
    

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33. Use cases
    Method swizzle (IIViewDeckController)
    JSON Model (Torin ‘s BaseModel)
    Message forwarding
    Meta programming
    

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34. Use cases
    Method swizzle
    

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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));
    

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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
    }
    

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37. Use cases
    JSON Model (Torin ‘s BaseModel)
    updateWithDictionary
    class_copyIvarList
    ivar_getName
    

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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”}];
    

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39. Message forwarding
    

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40. Use cases
    Meta programming
    ● Dynamic method naming
    ● Validation
    ● Template
    ● Mocking
    

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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
    

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42. Thank you
    Q&A
    

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