1、定义C函数：

void dynamicMethodIMP(idself, SEL _cmd)

{

    NSLog(@"蜗牛也疯狂");

}

2、重写函数+(BOOL)resolveInstanceMethod:(SEL)sel

+(BOOL)resolveInstanceMethod:(SEL)sel

{

    class_addMethod([selfclass], sel, (IMP)dynamicMethodIMP,"v@:");

    return [superresolveInstanceMethod:sel];

}

3、使用：

 SEL select =NSSelectorFromString(@"resolveThisMethodDynamically");

    [classresolveInstanceMethod:select];

    [[class instance] performSelector:select];