iOS Type Encodings

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使用runtime动态给一个对象添加方法的时候我们会发现有个参数不是很理解：那就是第四个 Type Encodings

class_addMethod([self class],sel, (IMP)eat,"v@:");

添加类方法

class_addMethod([self class],sel, (IMP)eat,"v#:");

后来查文档才知道是方法的返回值、参数类型

可如果仅仅这么理解那么就不全面。

通过Clang生成的C++代码查看得知，底层是通过objc_msgSend...函数调用，会默认有两个参数，一个是当前实例对象self 一个是方法_cmd

static void _I_DemoClass_TestFunction(DemoClass * self, SEL _cmd) {

    DemoClass * obj = objc_msgSend(objc_msgSend(objc_getClass("TestClass"), sel_registerName("alloc")), sel_registerName("init"));

}

这样我们就不难理解了为什么通过runtime动态给一个类添加方法的时候 Type Encodings 会多了两个默认的参数self、_cmd

下面是一张type encodings对应表

Table 6-1 Objective-C type encodings

Code

Meaning

c

A char

i

An int

s

A short

l

A long

l is treated as a 32-bit quantity on 64-bit programs.

q

A long long

C

An unsigned char

I

An unsigned int

S

An unsigned short

L

An unsigned long

Q

An unsigned long long

f

A float

d

A double

B

A C++ bool or a C99 _Bool

v

A void

*

A character string (char *)

@

An object (whether statically typed or typed id)

#

A class object (Class)

:

A method selector (SEL)

[array type]

An array

{name=type...}

A structure

(name=type...)

A union

bnum

A bit field of num bits

^type

A pointer to type

?

An unknown type (among other things, this code is used for function pointers)

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