【Objective-C Runtime动态加载】---动态创建

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](http://lib.csdn.net/base/1)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)];