UIScrollView不能滚动

        UIScrollview手动写的代码，滚动的相关属性都设了，可它就是不能滚动。原来是因为ContentSize跟初始化时的frame都设成了一样大。应该是frame高度要小于ContentSize的。

scrollView = [[UIScrollView alloc] initWithFrame:CGRectMake(0, 50, self.frame.size.width, self.frame.size.height)];
        scrollView.pagingEnabled = YES;
        [scrollView setScrollEnabled:YES];
        [scrollView setShowsHorizontalScrollIndicator:NO];
        [scrollView setShowsVerticalScrollIndicator:NO];
        [scrollView setContentSize:CGSizeMake(self.frame.size.width, 980)];
//        scrollView.delegate = self;
        [self addSubview:scrollView];