第十篇、让UIScrollView的滚动条常显

UIScrollView滚动条一直显示

1.我们知道滚动条是一个UIImageView, 滚动条隐藏是因为设置了alpha属性为0, 所有我们写一个UIImageView的分类

#define noDisableVerticalScrollTag 836913

#define noDisableHorizontalScrollTag 836914

@implementation UIImageView (WLScrollView)

- (void)setAlpha:(CGFloat)alpha

{

if (self.superview.tag == noDisableVerticalScrollTag) {

   if (alpha == 0 && self.autoresizingMask == UIViewAutoresizingFlexibleLeftMargin) {

       if (self.frame.size.width < 10 && 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 == 0 && self.autoresizingMask == UIViewAutoresizingFlexibleTopMargin) {

       if (self.frame.size.height < 10 && 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];

}

@end

2.写完分类之后, 我们在初始化UIScrollView的时候设置UIScrollView的tag为836913

3.要在UIScrollView数据绑定之后, 调用以下方法

- (void)flashScrollIndicators;             // displays the scroll indicators for a short time. This should be done whenever you bring the scroll view to front.

即调用以下方法

[scrollView reloadData];

[scrollView flashScrollIndicators];