让UIScrollView、UITableView的滚动条一直显示

先用xcode5.1.1或更低版本创建一个Category，如图：

然后拷贝以下代码到刚创建的UIImageView+ForScrollView.m文件中：

- (void) setAlpha:(float)alpha {

    if (self.superview.tag == noDisableVerticalScrollTag) {
        if (alpha ==  && self.autoresizingMask == UIViewAutoresizingFlexibleLeftMargin) {
            if (self.frame.size.width <  && self.frame.size.height > self.frame.size.width) {
                UIScrollView *sc = (UIScrollView*)self.superview;
                if (sc.frame.size.height < sc.contentSize.height) {
                    return;
                }
            }
        }
    }

    if (self.superview.tag == noDisableHorizontalScrollTag) {
        if (alpha ==  && self.autoresizingMask == UIViewAutoresizingFlexibleTopMargin) {
            if (self.frame.size.height <  && self.frame.size.height < self.frame.size.width) {
                UIScrollView *sc = (UIScrollView*)self.superview;
                if (sc.frame.size.width < sc.contentSize.width) {
                    return;
                }
            }
        }
    }

    [super setAlpha:alpha];
}

在.pch中定义这两个值：

#define noDisableVerticalScrollTag 836913
#define noDisableHorizontalScrollTag 836914

然后在你所用到UIScrollView、UITableView的视图控制器中：

#import "UIImageView+ForScrollView.h"

设置UIScrollView、UITableView：

    UIScrollView *scrollview = [[UIScrollView alloc]initWithFrame:self.view.bounds];
    scrollview.contentSize = CGSizeMake(, );
    scrollview.tag = noDisableVerticalScrollTag;
    [scrollview flashScrollIndicators];
    [self.view addSubview:scrollview];

    //---
    _tableView = [[UITableView alloc]initWithFrame:CGRectMake(, , , )];
    _tableView.delegate = self;
    _tableView.dataSource = self;
    _tableView.showsHorizontalScrollIndicator = YES;
    _tableView.tag = noDisableVerticalScrollTag;
    [_tableView flashScrollIndicators];
    [self.view addSubview:_tableView];

如此即可让UIScrollView、UITableView的滚动条一直显示。