ios - How to subtract minutes from a textfield displaying the time

Question

I have been doing a research with no luck on how to perform this operation and I still don’t get quite right the NSdate and the way to perform operations.

I have an app where a timeText(UITextField) is pressed a UIDatPicker pops up and the user can select the time desired with the wheel. Then, once doneBTN(from the toolBar) is pressed it populates the time desired on that textfield.

What I am looking for is to display on Tminus3 (UILabel), Tminus10 (UILabel), Tminus20 (UILabel) respectively, the result of the timeText (selected from the user) minus 3 min (Tminus3), minus 10 min (Tminus10), minus 20min (Tminus20) respectively on each label.

I.e. The user press the timeText and select the time, lets say 11:30. When I press updateBTN I would like to get the value of Tminus3.text = 11:27, Tminus10.text = 11:20, Tminus20.text = 11:10.

This is the initial code.

Thanks in advance

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var timeText: UITextField!
    let timePicker = UIDatePicker()
    
    @IBOutlet weak var Tminus3: UILabel!
    @IBOutlet weak var Tminus10: UILabel!
    @IBOutlet weak var Tminus20: UILabel!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        createTimeP()
    }
    func creteToolB() -> UIToolbar {
        let toolbar = UIToolbar()
        toolbar.sizeToFit()
        
        let doneBTN = UIBarButtonItem(barButtonSystemItem: .done, target: nil, action: #selector(donePressed))
        toolbar.setItems([doneBTN], animated: true)
     
        return toolbar
    }
    func createTimeP() {
        timePicker.preferredDatePickerStyle = .wheels
        timePicker.datePickerMode = .time
        timePicker.locale = NSLocale(localeIdentifier: "UTC") as Locale
        timePicker.minuteInterval = 5
        timeText.inputView = timePicker
        timeText.inputAccessoryView = creteToolB()
        
    }
    
    @objc func donePressed() {
        let timeFormatter = DateFormatter()
        timeFormatter.dateStyle = .none
        timeFormatter.timeStyle = .short
        timeFormatter.dateFormat = "HH:mm"
        self.timeText.text = timeFormatter.string(from: timePicker.date)
        self.view.endEditing(true)
        
    }
    
    @IBAction func **updateBTN**(_ sender: Any) {
    
        
    // from the timeText.text = "HH:mm" get the value —> minus3.text(label) minutes, minus10.text()label minutes, minus20.text(label) minutes.
      
        
    }
    
}

Answer 1

Try this:

import UIKit

class tViewController: UIViewController {

    @IBOutlet weak var timeText: UITextField!
    let timePicker = UIDatePicker()
    
    @IBOutlet weak var Tminus3: UILabel!
    @IBOutlet weak var Tminus10: UILabel!
    @IBOutlet weak var Tminus20: UILabel!

    var selectedDate: Date? = nil
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        createTimeP()
    }
    func creteToolB() -> UIToolbar {
        let toolbar = UIToolbar()
        toolbar.sizeToFit()
        
        let doneBTN = UIBarButtonItem(barButtonSystemItem: .done, target: nil, action: #selector(donePressed))
        toolbar.setItems([doneBTN], animated: true)
     
        return toolbar
    }
    func createTimeP() {
        timePicker.preferredDatePickerStyle = .wheels
        timePicker.datePickerMode = .time
        timePicker.locale = NSLocale(localeIdentifier: "UTC") as Locale
        timePicker.minuteInterval = 5
        timeText.inputView = timePicker
        timeText.inputAccessoryView = creteToolB()
        
    }
    
    @objc func donePressed() {
        let timeFormatter = DateFormatter()
        timeFormatter.dateStyle = .none
        timeFormatter.timeStyle = .short
        timeFormatter.dateFormat = "HH:mm"
        self.timeText.text = timeFormatter.string(from: timePicker.date)
        self.selectedDate = timePicker.date
        self.view.endEditing(true)
        
    }
    
    func getTime(date: Date) -> String {
        let timeFormatter = DateFormatter()
        timeFormatter.dateStyle = .none
        timeFormatter.timeStyle = .short
        timeFormatter.dateFormat = "HH:mm"
        return timeFormatter.string(from: date)
    }
    
    @IBAction func updateBTN(_ sender: Any) {
    
        if let selectedDate = self.selectedDate {
            let tminus3Date = Calendar.current.date(byAdding: .minute, value: -3, to: selectedDate)!
            let tminus10Date = Calendar.current.date(byAdding: .minute, value: -10, to: selectedDate)!
            let tminus20Date = Calendar.current.date(byAdding: .minute, value: -20, to: selectedDate)!
            
            self.Tminus3.text = getTime(date: tminus3Date)
            self.Tminus10.text = getTime(date: tminus10Date)
            self.Tminus20.text = getTime(date: tminus20Date)
        }
        
    }
    
}