How to turn on high-legibility alternates for system font in iOS?

Question

I would like to activate high-legibility alternate style set for San Francisco font in UITextView, using Swift 3.1.

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Answer 1

I managed to find a solution for activating high-legibility alternates in UITextView.

// TextViewController.swift

import UIKit

class TextViewController: UIViewController, UITextViewDelegate {
    // MARK: - Properties

    @IBOutlet weak var textView: UITextView!

    // MARK: - View Life Cycle

    override func viewDidLoad() {
        super.viewDidLoad()

        configureTextView()
    }

    // MARK: - Configuration

    func configureTextView() {

        // Activate high-legibility alternates for system font.
        let systemFontDescriptor = UIFont.systemFont(ofSize: 17).fontDescriptor
        let highLegibilityFontDescriptor = systemFontDescriptor.addingAttributes(
            [
                UIFontDescriptorFeatureSettingsAttribute:
                [
                    [
                        UIFontFeatureTypeIdentifierKey: kStylisticAlternativesType,
                        UIFontFeatureSelectorIdentifierKey: kStylisticAltSixOnSelector,
                    ],
                ]
            ]
        )
        textView.font = UIFont(descriptor: highLegibilityFontDescriptor, size: 17)
    }
}