How to create a left/right audio balance slider and have Voiceover read out custom values?

Question

I created an UISlider in Interface Builder, and want to use that to adjust the L/R audio volume balance between the two channels. This is what it looks like now:  My current code is as follows:

import UIKit

class StreamBalanceTableViewCell: AudioStreamTableViewCell {
static let identifier = "StreamBalanceTableViewCell"

override func awakeFromNib() {
    super.awakeFromNib()

    self.slider.minimumTrackTintColor = .gray
    self.slider.maximumTrackTintColor = .gray
}

@IBOutlet var slider: UISlider!
override func updateUI() {
    self.slider.value = self.audioInterface?.balance ?? 0.0
    self.slider.isEnabled = !(self.audioInterface?.muted ?? true)
}


@IBAction func sliderChanged(_ slider: UISlider) {
    self.audioInterface?.balance = slider.value
}

}

Within Interface Builder, I set the slider value to 0, the minimum to -1 and the maximum to 1, and set the 'User Interaction Enabled', 'Adjustable', and 'Allows Direct Interaction' traits. BUT when I turn Voiceover on, I get values reported in 10% increments, starting at “50%”.

I’d like the slider to behave as it does in this view from the General > Accessibility Settings screen:



In this position, Voiceover reads: “30% left, 70% right”

How do I accomplish what I'm after?

Thanks!!!

Answer 1

You can set the values that VoiceOver speaks with the view properties(via NSObject):

• .accessibilityLabel
• .accessibilityHint
• .accessibilityValue

VoiceOver will speak a slider's .accessibilityValue as the slider moves.

I set the slider to have a min of 0 and a max of 1 so that the value is in percentages, e.g. 0.35 is equivalent to 35%. Then I rounded off to the nearest 10%, so that VoiceOver would speak values like 70% left 30% right as the slider moved.

import UIKit

class ViewController: UIViewController {

    @IBOutlet var slider: UISlider!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        setSliderAccessibilityValue()           
    }

    @IBAction func sliderMoved(sender: Any?) {
        setSliderAccessibilityValue()    
    }

    func setSliderAccessibilityValue() {

        let right_percent = Int(
            round(slider.value * 10)  //=> round(0.2632 * 10) => round(2.632) => 3
        ) * 10  //=> 30
                                                //       30% = right %
        let left_percent = 100 - right_percent  //        |
                                                // left|..V......|right
                                                // balance: 70% left, 30% right
        let accValue = "\(left_percent)% left \(right_percent)% right"           
        slider.accessibilityValue = accValue

    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }
}