a.使用objc_allocateClassPair创建一个类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添加一个成员变量

    NSUInteger size;

    NSUInteger alignment;

    NSGetSizeAndAlignment("*", &size, &alignment);

    class_addIvar(kclass, "expression", size, alignment, "*");

    注:

    1.type定义参考:https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/ObjCRuntimeGuide/Articles/ocrtTypeEncodings.html

    2."*"星号代表字符(),iOS字符为4位，并采用4位对齐kclass

c.使用class_addMethod添加成员方法

    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定义参考:https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/ObjCRuntimeGuide/Articles/ocrtTypeEncodings.html

    2."v@:@",解释v-返回值void类型,@-self指针id类型,:-SEL指针SEL类型,@-函数第一个参数为id类型

    3."@@:",解释@-返回值id类型,@-self指针id类型,:-SEL指针SEL类型,

d.注册到运行时环境

    objc_registerClassPair(kclass);

e.实例化类

    id instance = [[kclass alloc] init];

f.给变量赋值

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

g.获取变量值

    void * value = NULL;

    object_getInstanceVariable(instance, "expression", &value); 

h.调用函数

    [instance performSelector:@selector(getExpressionFormula)];