runtime运行时之方法method

a Method is a combination of a selector and an implement

method 组成结构体

runtime之方法(method)

runtime 参考https://developer.apple.com/library/mac/documentation/Cocoa/Reference/ObjCRuntimeRef/

a Method is a combination of a selector and an implement

method 组成结构体

runtime 处理method相关方法

方法的invoke objc_msgSend(receiver, selector, arg1, arg2, …)

typedef struct objc_selector *SEL;a Selector is the name of the method used to identity 方法的签名ID
比如 setObject:forKey: setName:age: 这些形式的字符串就代表了sel的标识，但根据这些不知道这个方法参数的类型是什么
SEL aSelector = @selector(doSomething:) or SEL aSelector = NSSelectorFromString(@”doSomething:”)

method_types 方法的参数类型和返回值类型 比如方法setName:age:的参数是这样 v16@0:4@8i12 那些数字可能代表地址的偏移量

Implement -> id (*IMP)(id, SEL, …) 函数指针变量，指向方法实现代码块的入口地址

Implementation - the actual executable code block of a method. it’s a function pointer (an IMP).

a selector is like a key in in a hash table(NSDictionary) , and the value is the IMP of the method
class的方法列表其实是一个字典，key为selectors，IMPs为value。一个IMP是指向方法在内存中的实现

利用runtime提供的method系列方法，可以很明显的知道可以将两个方法的实现exchange，这就是所谓的swizzle

swizzle : swizzling allows you to replace a method in an existing class with one of your own making . This approach can lead to a lot of unexpected behavior ,so it should be used very sparingly.

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