UIScrollView - how is showsHorizontalScrollIndicator calculated? - ios

Question

If showsHorizontalScrollIndicator is enabled, a small horizontal indicator is displayed at the bottom of the UIScrollView. I was wondering if anyone could tell me how this is calculated. The reason being, I want to display a custom indicator in a horizontal navigation system if there is content left/right, show/hiding when content is available.

Answer 1

I just use scrollView.contentOffset.x. If you want to know what page you are on, you divide by your page width (assuming you have a standard width). So
int currentPage=(int)scrollView.contentOffset.x/SCREEN_WIDTH; for example. Now if you want to display a position indicator, like in the iOS homepage, you can do it in a loop in
-(void)scrollViewDidScroll:(UIScrollView *)sender something like
currentPage=(int)scrollView.contentOffset.x/SCREEN_WIDTH;
for(int i=0; i<pageCount; i++){
if(i==currentPage)//display a filled in 'o'
else //display an empty 'o'
}
Oh, BTW, -(void)scrollViewDidScroll:(UIScrollView *)sender is not called when the UIScrollView is initially loaded, so you perhaps should call it yourself (in order to display the indicator before the user has scrolled). You can also use scrollView.contentOffset.y off course, so you could easily adapt this to show a '+' shaped arrangement of 'o's, hinting at content above and below also.

Answer 2

I used the following solution. Not the prettiest, but it seems to work. Requires UIScrollViewDelegate.
-(void)scrollViewDidScroll:(UIScrollView *)sender
{
[NSObject cancelPreviousPerformRequestsWithTarget:self];
[self scrollViewDidEndScrollingAnimation:subNavigation];
}
-(void)scrollViewDidEndScrollingAnimation:(UIScrollView *)scrollView
{
[NSObject cancelPreviousPerformRequestsWithTarget:self];
if (scrollView.contentOffset.x <= 0) {
[self scrollViewReachedLeftBound];
} else if (scrollView.contentOffset.x >= 300) {
[self scrollViewReachedRightBound];
} else {
[leftArrow setHidden:NO];
[rightArrow setHidden:NO];
}
}
- (void)scrollViewReachedLeftBound
{
[leftArrow setHidden:YES];
[rightArrow setHidden:NO];
}
- (void)scrollViewReachedRightBound
{
[leftArrow setHidden:NO];
[rightArrow setHidden:YES];
}