ASJColoredScrollIndicators

The stock UIScrollView provides limited options to customize its scroll indicators, with a sole enum UIScrollViewIndicatorStyle that may prove lacking. It makes sense sometimes to paint the indicators as per the app's theme to give it a little extra. This small utility provides a UIScrollView category with a lightweight solution to apply a color to the scroll indicators.

After coming across JTSScrollIndicator and looking at its implementation, I felt there could be an easier way to do this. My implementation gets a hold of the scroll indicator objects themselves and paints them to the desired color. I feel this is a much more simple and direct approach.

Installation

CocoaPods is the preferred way to install this library. Add this command to your Podfile:

pod 'ASJColoredScrollIndicators'

Usage

Import ASJColoredScrollIndicators.h and set this property to any UIScrollView:

@property (nullable, strong, nonatomic) UIColor *scrollIndicatorColor UI_APPEARANCE_SELECTOR;

Paints both the horizontal and vertical scroll indicators to the desired color.

You may also set the property via UIAppearance to set the color globally:

[UIScrollView appearance].scrollIndicatorColor = [UIColor blueColor];

Since this is a category on UIScrollView, it works with all subclasses:

• UITableView
• UICollectionView
• UITextView

How it works

UIScrollView's scroll indicators are not publicly available. Looking at its subviews, we find two UIImageViews that appear to be the indicators. Each has either their width or height 2.5 pts. Interestingly, no matter whether your view scrolls in both directions, the vertical and horizontal indicator objects are present.

So it would seem that modifying these UIImageViews would do the job. But no! What I found is that these objects are changed when the scrolling is active; their memory addresses were different. This happens every time. You could check the indicators in scrollViewDidScroll: or scrollViewWillBeginDragging, the addresses there are the same, but not the same when the UIScrollView initially loaded.

When this was clear, the rest was pretty simple. I tried to change the background color of those UIImageViews but the effect was not nice; there still was some transparency. I ended up removing the image's color information and setting a background color to the UIImageView with some rounding to shape it look like a default indicator. Voilà!

This color change is done exactly once, when the UIScrollView is about to be scrolled for the very first time.

Note: Since iOS 13, the indicators are no longer UIImageViews but a private subclass of UIView called _UIScrollViewScrollIndicator.

Credits

• To Shashank Pali for his perseverence to unite this functionality under a single category.

To-do

• Add UICollectionView and UITextView.
• Find a way to combine the four in one class.

License

ASJColoredScrollIndicators is available under the MIT license. See the LICENSE file for more info.