iOS：KVO

KVO的原理
1，动态生成子类：NSKvoNotifying_xx
2，isa只指向态子类
3，观察的是 setter
4，动态子类重写了很多方法 setter class dealloc _isKVOA
5，移除观察的时候 isa 指向回来
6，动态子类不会销毁

- (void)log:(Class)class
{
    unsigned int count = 0;
    Method *methodList = class_copyMethodList(class, &count);
    for (int i = 0; i < count; i++ ) {
        Method method = methodList[i];
        SEL sel = method_getName(method);
        IMP imp = class_getMethodImplementation(class, sel);
        NSLog(@"%@-%p",NSStringFromSelector(sel),imp);
        
    }
    free(methodList);
}