Decrease the value of the variable containing the current time with UISlider - ios

Question

I don't know how to make the current time value (returned by the dateFormatter variable) change when scrolling the slider.
I tried to convert the dateFormatter variable to double but without success.
var c: Double
c = Double(dateFormatter.string(from: Date())
I would like to decrease the value of the time -1 hour for each shift of the slider thumb.
The changeTime function has to take care of changing the time value when moving the slider.
#IBOutlet weak var sliderTime: UISlider!
#IBOutlet var labelTime: UILabel!
var timer = Timer()
var dateFormatter = DateFormatter()
override func viewDidLoad()
{
dateFormatter.timeStyle = .short
labelTime.text = dateFormatter.string(from: Date())
timer = Timer.scheduledTimer(timeInterval: 60, target: self, selector: #selector(updateTimeLabel), userInfo: nil, repeats: true);
}
#objc func updateTimeLabel() {
labelTime.text = dateFormatter.string(from: Date())
}
#IBAction func changeTime(_ sender: Any) {
}

Answer 1

Swift 5
Whenever you update the date, decrease the number of hours dedicated by slider from the current date, try this:
class ViewController: UIViewController
{
#IBOutlet weak var simpleSlider: UISlider!
#IBOutlet weak var dateLabel: UILabel!
var timer = Timer()
var currentSliderStep: Int = 0
var dateFormatter = DateFormatter()
override func viewDidLoad()
{
dateFormatter.timeStyle = .short
labelTime.text = dateFormatter.string(from: Date())
timer = Timer.scheduledTimer(timeInterval: 60, target: self, selector: #selector(updateTimeLabel), userInfo: nil, repeats: true);
}
#objc func updateTimeLabel()
{
let newDate = Calendar.current.date(byAdding: .hour, value: -currentSliderStep, to: Date())!
labelTime.text = dateFormatter.string(from: newDate)
}
#IBAction func sliderMoved(sender: AnyObject)
{
let value = simpleSlider.value
let step: Float = 1
let roundedValue = round(value / step) * step
currentSliderStep = Int(roundedValue)
}
}
Note: With the Slider, the "Primary Action Triggered" event is triggered when it is adjusted. This is the perfect event to handle (link this event to sliderMoved).