Add border for dots in UIPageControl

Swift 4. You can assign borderColor and then observe currentPage property to change dots' border:

class CustomPageControl: UIPageControl {

    var borderColor: UIColor = .clear

    override var currentPage: Int {
        didSet {
            updateBorderColor()
        }
    }

    func updateBorderColor() {
        subviews.enumerated().forEach { index, subview in
            if index != currentPage {
                subview.layer.borderColor = borderColor.cgColor
                subview.layer.borderWidth = 1
            } else {
                subview.layer.borderWidth = 0
            }
        }
    }

}

I am using SMPageControl. It's a really awesome Framework written in Objective-C, so it's capable with Swift 2 and Swift 3.

The usage is completely simple:

pod 'SMPageControl'

Then in your PageViewController:

import SMPageControl

class MyController: UIPageViewController {

     var pageControl = SMPageControl()

     override func viewDidLoad() {
        super.viewDidLoad()

        stylePageControl()
    }

private func stylePageControl() {

    pageControl = SMPageControl(frame: CGRect(x: 0, y: self.view.frame.size.height - 50, width: self.view.frame.size.width, height: 50))
    pageControl.numberOfPages = yourPageControllerArray.count

//  the first (first) picture is the item in the bar, that is unused
//  the second (currentFirst) is an item that we use, when this is the current active page
//  in this example, we don't have dots, but we use "pictues" as dots

    let first = UIImage(named: "pageHome")?.imageWithColor(UIColor.grayColor())
    let currentFirst = first?.imageWithColor(UIColor.whiteColor())

    pageControl.setImage(first, forPage: 0)
    pageControl.setCurrentImage(currentFirst, forPage: 0)

    let second = UIImage(named: "pageMusic")?.imageWithColor(UIColor.grayColor())
    let currentSecond = second?.imageWithColor(UIColor.whiteColor())

    pageControl.setImage(second, forPage: 1)
    pageControl.setCurrentImage(currentSecond, forPage: 1)

    pageControl.indicatorMargin = 30.0 // this is the space between the dots

    self.view.addSubview(pageControl)
}

UIImage Extension I've used:

extension UIImage {

    func imageWithColor(color1: UIColor) -> UIImage {
        UIGraphicsBeginImageContextWithOptions(self.size, false, self.scale)
        color1.setFill()

        let context = UIGraphicsGetCurrentContext()! as CGContextRef
        CGContextTranslateCTM(context, 0, self.size.height)
        CGContextScaleCTM(context, 1.0, -1.0);
        CGContextSetBlendMode(context, CGBlendMode.Normal)

        let rect = CGRectMake(0, 0, self.size.width, self.size.height) as CGRect
        CGContextClipToMask(context, rect, self.CGImage!)
        CGContextFillRect(context, rect)

        let newImage = UIGraphicsGetImageFromCurrentImageContext()! as UIImage
        UIGraphicsEndImageContext()

        return newImage
    }

}

The result looks like this:

Now we could of course use colored dots as the images, (blank colored as unused and color-filled as used) then we would have the asked result.

Just add this two lines and add the desired image !!

pageControl.currentPageIndicatorTintColor  = UIColor.init(patternImage: UIImage(named: "slider_selected")!)

pageControl.pageIndicatorTintColor =  UIColor.init(patternImage: UIImage(named: "slider")!)

Please try this custom subclassing of UIPageControl. iOS 14 allows setting indicator image with SFSymbol.

class BorderedPageControl: UIPageControl {

    var selectionColor: UIColor = .black
    
    override var currentPage: Int {
        didSet {
            updateBorderColor()
        }
    }
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        currentPageIndicatorTintColor = selectionColor
    }
    
    required init?(coder: NSCoder) {
        super.init(coder: coder)
    }
    
    func updateBorderColor() {
        if #available(iOS 14.0, *) {
            let smallConfiguration = UIImage.SymbolConfiguration(pointSize: 8.0, weight: .bold)
            let circleFill = UIImage(systemName: "circle.fill", withConfiguration: smallConfiguration)
            let circle = UIImage(systemName: "circle", withConfiguration: smallConfiguration)
            for index in 0..<numberOfPages {
                if index == currentPage {
                    setIndicatorImage(circleFill, forPage: index)
                } else {
                    setIndicatorImage(circle, forPage: index)
                }
            }
            pageIndicatorTintColor = selectionColor
        } else {
            subviews.enumerated().forEach { index, subview in
                if index != currentPage {
                    subview.layer.borderColor = selectionColor.cgColor
                    subview.layer.borderWidth = 1
                } else {
                    subview.layer.borderWidth = 0
                }
            }
        }
    }
}

Swift 5 version

func customPageControl(dotFillColor: UIColor, dotBorderColor: UIColor, dotBorderWidth: CGFloat) {
    for (pageIndex, dotView) in self.subviews.enumerated() {
        dotView.backgroundColor = currentPage == pageIndex ? dotFillColor : .clear
        dotView.layer.cornerRadius = dotView.frame.size.height / 2
        dotView.layer.borderColor = dotBorderColor.cgColor
        dotView.layer.borderWidth = dotBorderWidth
    }
}

Luke Rogers's solution, written in objective-c:

-(UIImage *) outlinedEllipse:(CGSize)size color: (UIColor*) lineColor width:(CGFloat) lineWidth {
        UIGraphicsBeginImageContextWithOptions(size, false, 0.0);

        CGContextRef context = UIGraphicsGetCurrentContext();
        if (context == NULL) {
            return NULL;
        }

        CGContextSetStrokeColorWithColor(context, lineColor.CGColor);
        CGContextSetLineWidth(context, lineWidth);
        // Inset the rect to account for the fact that strokes are
        // centred on the bounds of the shape.

        CGRect rect = CGRectInset(CGRectMake(0, 0, 7.0f, 7.0f), lineWidth * 0.5, lineWidth * 0.5);
        CGContextAddEllipseInRect(context, rect);
        CGContextStrokePath(context);

        UIImage* image = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
        return image;
}

Modern Luke Rogers (elk_cloner says it's not modern enough for ios14)

extension UIImage
{
// https://stackoverflow.com/questions/35842040/add-border-for-dots-in-uipagecontrol
    // modernized Luke Rogers
    class func outlinedEllipse(size: CGSize, color: UIColor, lineWidth: CGFloat = 1.0) -> UIImage? {

        let renderer = UIGraphicsImageRenderer(size: size)
        let image = renderer.image { context in

            color.setFill()
            
            context.cgContext.setLineWidth(lineWidth)
            // Inset the rect to account for the fact that strokes are
            // centred on the bounds of the shape.
            let rect = CGRect(origin: .zero, size: size).insetBy(dx: lineWidth * 0.5, dy: lineWidth * 0.5)
            context.cgContext.strokeEllipse(in: rect)
        }
        return image
    }
    
}