self and super in objc

Obj-C中的self与super

twitter:@vonbo

11年1月24日星期一

输出结果？


输出结果？


输出结果？

self class is Derivedsuper class is Derived


obj-c的方法调用• [self class] or [super class]

• self 是类的隐藏的参数，指向当前当前调用方法的对象

• super是一个“编译器指示符”，它和self指向的是相同的消息接收者，不同的是，super告诉编译器，当调用class的方法时，要去调用父类的方法，而不是本类里的


C函数方法调用 -1

• Sending Messages

• When it encounters a method invocation, the compiler might generate a call to any of several functions to perform the actual message dispatch, depending on the receiver, the return value, and the arguments.

• You can use these functions to dynamically invoke methods from your own plain C code, or to use argument forms not permitted by NSObject’s perform… methods. These functions are declared in /usr/include/objc/objc-runtime.h.


C函数方法调用 -2• objc_msgSend sends a message with a simple

return value to an instance of a class.

• objc_msgSend_stret sends a message with a data-structure return value to an instance of a class.

• objc_msgSendSuper sends a message with a simple return value to the superclass of an instance of a class.

• objc_msgSendSuper_stret sends a message with a data-structure return value to the superclass of an instance of a class.uperclass of an instance of a class.


objc_msgSend

• 函数定义：• id objc_msgSend(id theReceiver, SEL

theSelector, ...)

• [self class]：

• theReceiver -> self

• SEL -> class


objc_msgSendSuper

• 函数定义：• id objc_msgSendSuper(struct objc_super

*super, SEL op, ...)

• [super class]

• objc_super -> some struct?

• SEL -> class


objc_super

struct objc_super {

id receiver;

Class superClass;

}


objc_msgSendSuper

• [super class]：

• 构建objc_super结构体，receiver = self，superClass = Base

• 调用objc_msgSendSuper方法，通过objc_super -> superClass找到selector

• 将此selector作用到objc_super -> receiver上


That is ...• [self class]

• objc_msgSend(receiver, class)

• receiver = Derived, “class” selector is from NSObject

• [super class]

• objc_msgSendSuper(objc_super, class)

• ==> objc_msgSend(objc_super -> receiver, class)

• receiver = Derived, “class” selector is from NSObject

• NSObject的这个class方法，就是返回receiver的class


That is ...

• [self class]

• objc_msgSend(receiver, class)

• receiver = Derived, class method is from NSObject

• [super class]

• objc_msgSendSuper(objc_super, class)

• ==> objc_msgSend(objc_super -> receiver, class)

• receiver = Derived, class method from NSObject

• NSObject的这个class方法，就是返回receiver的class

So ... [self class] ‘s output is Derived [super class] ‘s output is Derived too !


How to get super class’s name?

• [self superclass]

• NSLog(@"super class is %@", [self superclass]);

• The output is “Base” !


The End


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self and super in objc