运行时创建类

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.html2."*"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.html2."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)];