CustomSegmentedControl.swift

//: Playground - noun: a place where people can play

import UIKit
import PlaygroundSupport

class Responder: NSObject {
    @objc func segmentedControlValueChanged(_ sender: UISegmentedControl) {
        UIView.animate(withDuration: 0.3) {
            buttonBar.frame.origin.x = (segmentedControl.frame.width / CGFloat(segmentedControl.numberOfSegments)) * CGFloat(segmentedControl.selectedSegmentIndex)
        }
    }
}

let responder = Responder()

// Container view
let view = UIView(frame: CGRect(x: 0, y: 0, width: 400, height: 100))
view.backgroundColor = .white

let segmentedControl = UISegmentedControl()
// Add segments
segmentedControl.insertSegment(withTitle: "One", at: 0, animated: true)
segmentedControl.insertSegment(withTitle: "Two", at: 1, animated: true)
segmentedControl.insertSegment(withTitle: "Three", at: 2, animated: true)
// First segment is selected by default
segmentedControl.selectedSegmentIndex = 0

segmentedControl.backgroundColor = .clear
segmentedControl.tintColor = .clear
segmentedControl.setTitleTextAttributes([
    NSAttributedStringKey.font : UIFont(name: "DINCondensed-Bold", size: 18),
    NSAttributedStringKey.foregroundColor: UIColor.lightGray
    ], for: .normal)

segmentedControl.setTitleTextAttributes([
    NSAttributedStringKey.font : UIFont(name: "DINCondensed-Bold", size: 18),
    NSAttributedStringKey.foregroundColor: UIColor.orange
    ], for: .selected)

// This needs to be false since we are using auto layout constraints
segmentedControl.translatesAutoresizingMaskIntoConstraints = false

let buttonBar = UIView()
// This needs to be false since we are using auto layout constraints
buttonBar.translatesAutoresizingMaskIntoConstraints = false
buttonBar.backgroundColor = UIColor.orange

// Add the segmented control to the container view
view.addSubview(segmentedControl)
view.addSubview(buttonBar)

// Constrain the segmented control to the top of the container view
segmentedControl.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
// Constrain the segmented control width to be equal to the container view width
segmentedControl.widthAnchor.constraint(equalTo: view.widthAnchor).isActive = true
// Constrain the height of the segmented control to an arbitrarily chosen value
segmentedControl.heightAnchor.constraint(equalToConstant: 40).isActive = true

// Constrain the top of the button bar to the bottom of the segmented control
buttonBar.topAnchor.constraint(equalTo: segmentedControl.bottomAnchor).isActive = true
buttonBar.heightAnchor.constraint(equalToConstant: 5).isActive = true
// Constrain the button bar to the left side of the segmented control
buttonBar.leftAnchor.constraint(equalTo: segmentedControl.leftAnchor).isActive = true
// Constrain the button bar to the width of the segmented control divided by the number of segments
buttonBar.widthAnchor.constraint(equalTo: segmentedControl.widthAnchor, multiplier: 1 / CGFloat(segmentedControl.numberOfSegments)).isActive = true

segmentedControl.addTarget(responder, action: #selector(responder.segmentedControlValueChanged(_:)), for: UIControlEvents.valueChanged)

PlaygroundPage.current.liveView = view