a.使用objc_allocateClassPair創(chuàng)建一個(gè)類Class

const char * className = "Calculator";
    Class kclass = objc_getClass(className);
    if (!kclass) 
    {
       Class superClass = [NSObject class]; 
       kclass = objc_allocateClassPair(superClass, className, 0);
    }

b.使用class_addIvar添加一個(gè)成員變量

NSUInteger size;   
NSUInteger alignment;
NSGetSizeAndAlignment("*", &size, &alignment);
class_addIvar(kclass, "expression", size, alignment, "*");
注:
    1.type定義參考:https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/ObjCRuntimeGuide/Articles/ocrtTypeEncodings.html
    2."*"星號(hào)代表字符(),[iOS](http://lib.csdn.net/base/1)字符為4位，并采用4位對(duì)齊kclass

c.使用class_addMethod添加成員方法

class_addMethod(kclass, @selector(setExpressionFormula:), (IMP)setExpressionFormula, "v@:@");
class_addMethod(kclass, @selector(getExpressionFormula), (IMP)getExpressionFormula, "@@:");
static void setExpressionFormula(id self, SEL cmd, id value) {
       NSLog(@"call setExpressionFormula");
    }
static void getExpressionFormula(id self, SEL cmd) {
        NSLog(@"call getExpressionFormula");
    } 
注:
    1.type定義參考:https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/ObjCRuntimeGuide/Articles/ocrtTypeEncodings.html
    2."v@:@",解釋v-返回值void類型,@-self指針id類型,:-SEL指針SEL類型,@-函數(shù)第一個(gè)參數(shù)為id類型
    3."@@:",解釋@-返回值id類型,@-self指針id類型,:-SEL指針SEL類型,

d.注冊(cè)到運(yùn)行時(shí)環(huán)境

objc_registerClassPair(kclass);

e.實(shí)例化類

 id instance = [[kclass alloc] init];

f.給變量賦值

object_setInstanceVariable(instance, "expression", "1+1"); 

g.獲取變量值

void * value = NULL;
object_getInstanceVariable(instance, "expression", &value); 

h.調(diào)用函數(shù)

 [instance performSelector:@selector(getExpressionFormula)];