UIScrollView - showing the scroll bar

Question

No, you can't make them always show, but you can make them temporarily flash.

[myScrollView flashScrollIndicators];

They are scroll indicators, not scroll bars. You can't use them to scroll.

my solution for show scroll indicators all the time

#define noDisableVerticalScrollTag 836913
#define noDisableHorizontalScrollTag 836914

@implementation UIImageView (ForScrollView)

- (void) setAlpha:(float)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

UPDATE: This solution cause some issues on 64-bit. For more detail look here

As far as I know, this isn't possible. The only API call which controls displaying the scroll indicator is showsVerticalScrollIndicator and that can only disable displaying the indicator altogether.

You could flashScrollIndicators when the view appears so that the user knows where in the scroll view they are.

This one worked for me:

#define noDisableVerticalScrollTag 836913
#define noDisableHorizontalScrollTag 836914

@implementation UIImageView (ForScrollView) 

- (void) setAlpha:(float)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

I got this snippet from here: http://www.developers-life.com/scrollview-with-scrolls-indicators-which-are-shown-all-the-time.html

Swift 3+

1) Timer

var timerForShowScrollIndicator: Timer?

2) Methods

/// Show always scroll indicator in table view
func showScrollIndicatorsInContacts() {
    UIView.animate(withDuration: 0.001) {
        self.tableView.flashScrollIndicators()
    }
}

/// Start timer for always show scroll indicator in table view
func startTimerForShowScrollIndicator() {
    self.timerForShowScrollIndicator = Timer.scheduledTimer(timeInterval: 0.3, target: self, selector: #selector(self.showScrollIndicatorsInContacts), userInfo: nil, repeats: true)
}

/// Stop timer for always show scroll indicator in table view
func stopTimerForShowScrollIndicator() {
    self.timerForShowScrollIndicator?.invalidate()
    self.timerForShowScrollIndicator = nil
}

3) Use

startTimerForShowScrollIndicator in viewDidAppear

stopTimerForShowScrollIndicator in viewDidDisappear

I want to offer my solution. I don't like the most popular variant with category (overriding methods in category can be the reason of some indetermination what method should be called in runtime, since there is two methods with the same selector). I use swizzling instead. And also I don't need to use tags.

Add this method to your view controller, where you have scroll view (self.categoriesTableView property is a table view where I want to show scroll bars)

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    // Do swizzling to turn scroll indicator always on
    // Search correct subview with vertical scroll indicator image across tableView subviews
    for (UIView * view in self.categoriesTableView.subviews) {
        if ([view isKindOfClass:[UIImageView class]]) {
            if (view.alpha == 0 && view.autoresizingMask == UIViewAutoresizingFlexibleLeftMargin) {
                if (view.frame.size.width < 10 && view.frame.size.height > view.frame.size.width) {
                    if (self.categoriesTableView.frame.size.height < self.categoriesTableView.contentSize.height) {
                        // Swizzle class for found imageView, that should be scroll indicator
                        object_setClass(view, [AlwaysOpaqueImageView class]);
                        break;
                    }
                }
            }
        }
    }
    // Search correct subview with horizontal scroll indicator image across tableView subviews
    for (UIView * view in self.categoriesTableView.subviews) {
        if ([view isKindOfClass:[UIImageView class]]) {
            if (view.alpha == 0 && view.autoresizingMask == UIViewAutoresizingFlexibleTopMargin) {
                if (view.frame.size.height < 10 && view.frame.size.height < view.frame.size.width) {
                    if (self.categoriesTableView.frame.size.width < self.categoriesTableView.contentSize.width) {
                        // Swizzle class for found imageView, that should be scroll indicator
                        object_setClass(view, [AlwaysOpaqueImageView class]);
                        break;
                    }
                }
            }
        }
    }
    // Ask to flash indicator to turn it on
   [self.categoriesTableView flashScrollIndicators];
}

Add new class

@interface AlwaysOpaqueImageView : UIImageView
@end

@implementation AlwaysOpaqueImageView

- (void)setAlpha:(CGFloat)alpha {
    [super setAlpha:1.0];
}

@end

The scroll indicator (vertical scroll indicator in first for cycle and horizontal in second for cycle) will be always at the screen. If you need only one indicator, left only this for cycle in code and remove another one.