近期RAC中給scrollview添加觀察者费坊，接收滑動(dòng)的數(shù)值時(shí)發(fā)現(xiàn)返回的類型為：NSConcreteValue，我們需要轉(zhuǎn)化為我們熟知的CG類型（CGPoint，CGRect等）乐设。以下以CGPoint為例
UIScrollView *scrolView = [[UIScrollView alloc] initWithFrame:CGRectMake(0, 0, 200, 400)];
scrolView.contentSize = CGSizeMake(200, 800);
scrolView.backgroundColor = [UIColor greenColor];
[self.view addSubview:scrolView];
[RACObserve(scrolView, contentOffset) subscribeNext:^(id x) {
//此處接收的打印的x為NSConcreteValue
//如下轉(zhuǎn)為CGPoint類型，若轉(zhuǎn)化為CGRect绎巨，對(duì)應(yīng) [(NSValue *)x CGRectValue]
CGPoint point = [(NSValue *)x CGPointValue];
}];
