How to save user preference of dark or light mode - swift

Question

I have these buttons in my app so user can switch from light to dark mode in the app, how can I save this preference so whichever mode the user selected will still be active the next time they open the app?
I'm on Xcode 14.2
Code example please.
#IBAction func darkButton(_ sender: Any) {
overrideUserInterfaceStyle = .dark
}
#IBAction func lightButton(_ sender: Any) {
overrideUserInterfaceStyle = .light
}
Full code below
import UIKit
class ViewController: UIViewController {
// All Input Texts
#IBOutlet weak var machineODInputText: UITextField!
#IBOutlet weak var pipeODInputText: UITextField!
#IBOutlet weak var pipeLengthInputText: UITextField!
#IBOutlet weak var driveLengthInputText: UITextField!
#IBOutlet weak var muckUpInputText: UITextField!
#IBOutlet weak var jackingSpeedInputText: UITextField!
#IBOutlet weak var weightOfBenoBagInputText: UITextField!
#IBOutlet weak var noOfBenoBagsInputText: UITextField!
#IBOutlet weak var benoQtyForTanksInputText: UITextField!
#IBOutlet weak var noOfBenoBagsPerPalletInputText: UITextField!
// All Result Texts
#IBOutlet weak var lubricationPumpSpeedResult: UILabel!
#IBOutlet weak var volumePerMeterResult: UILabel!
#IBOutlet weak var volumePerPipeResult: UILabel!
#IBOutlet weak var volumeForDriveResult: UILabel!
#IBOutlet weak var benoQtyForLubricationResult: UILabel!
#IBOutlet weak var benoQtyForDriveResult: UILabel!
#IBOutlet weak var noOfPalletsForDriveResult: UILabel!
// All Buttons
#IBAction func lightButton(_ sender: Any) {
overrideUserInterfaceStyle = .light
UserDefaults.standard.set("light", forKey: "mode")
}
#IBAction func darkButton(_ sender: Any) {
overrideUserInterfaceStyle = .dark
UserDefaults.standard.set("dark", forKey: "mode")
}
#IBAction func calculateButton(_ sender: Any) {
let formatter = NumberFormatter()
formatter.numberStyle = .decimal
formatter.maximumFractionDigits = 0
let formatter2 = NumberFormatter()
formatter2.numberStyle = .decimal
formatter2.maximumFractionDigits = 2
let pi = Double.pi / 4
let TBMOD = (Double(machineODInputText.text!) ?? 1) / 1000.0
let pipeOD = (Double(pipeODInputText.text!) ?? 1) / 1000.0
let muckup = (Double(muckUpInputText.text!) ?? 2.5)
let advanceSpeed = (Double(jackingSpeedInputText.text!) ?? 1)
let volPerPipe = (Double(pipeLengthInputText.text!) ?? 1)
let volForDrive = (Double(driveLengthInputText.text!) ?? 1)
let noOfBenoBagsForLub = (Double(noOfBenoBagsInputText.text!) ?? 1)
let weightOfEachBenoBag = (Double(weightOfBenoBagInputText.text!) ?? 1)
let amountOfBenoBagsInTamks = (Double(benoQtyForTanksInputText.text!) ?? 1)
let noOfBenoBagsPerPallet = (Double(noOfBenoBagsPerPalletInputText.text!) ?? 1)
// Calculate Volume per Meter (Ltr per meter)
let volPerMtrResults1 = ((pi * (TBMOD) * (TBMOD)) - (pi * (pipeOD) * (pipeOD))) * muckup * 1000
let volPerMtrResult = formatter.string (from: NSNumber(value: volPerMtrResults1))
volumePerMeterResult.text = volPerMtrResult
// Calculate Lubrication Pump Capacity (Ltr per min)
let pumpCapacityResults1 = (advanceSpeed / 1000) * volPerMtrResults1
let lubPerMtrResult = formatter.string(from: NSNumber(value: pumpCapacityResults1))
lubricationPumpSpeedResult.text = lubPerMtrResult
// Calculate Volume per pipe (M³ per pipe)
let volPerPipeResults1 = (volPerMtrResults1 / 1000) * volPerPipe
let volPerPipeResult = formatter2.string(from: NSNumber(value: volPerPipeResults1))
volumePerPipeResult.text = volPerPipeResult
// Calculate Volume for drive (M³ for drive)
let volPerDriveResults1 = (volPerMtrResults1 / 1000) * volForDrive
let volPerDriveResult = formatter.string(from: NSNumber(value: volPerDriveResults1))
volumeForDriveResult.text = volPerDriveResult
// Calculate Amount of beno for lubrication
let ammountOfBenoForLubResults1 = noOfBenoBagsForLub * volPerDriveResults1 * weightOfEachBenoBag
let ammountOfBenoForLubResult = formatter.string(from: NSNumber(value: ammountOfBenoForLubResults1))
benoQtyForLubricationResult.text = ammountOfBenoForLubResult
// Calculate beno quantity for drive
let amountOfBenoForDriveResults1 = ammountOfBenoForLubResults1 + (amountOfBenoBagsInTamks * 1000)
let amountOfBenoForDriveResult = formatter.string(from: NSNumber(value: amountOfBenoForDriveResults1))
benoQtyForDriveResult.text = amountOfBenoForDriveResult
// Calculate number of pallets for drive
let ammountOfBenoPerPalletResults1 = amountOfBenoForDriveResults1 / weightOfEachBenoBag / noOfBenoBagsPerPallet
let ammountOfBenoPerPalletResult = formatter2.string(from: NSNumber(value: ammountOfBenoPerPalletResults1))
noOfPalletsForDriveResult.text = ammountOfBenoPerPalletResult
UserDefaults.standard.set(machineODInputText.text, forKey: "TBMOD")
UserDefaults.standard.set(pipeODInputText.text, forKey: "pipeOD")
UserDefaults.standard.set(muckUpInputText.text, forKey: "muckUp")
UserDefaults.standard.set(jackingSpeedInputText.text, forKey: "speed")
UserDefaults.standard.set(pipeLengthInputText.text, forKey: "pipeLength")
UserDefaults.standard.set(driveLengthInputText.text, forKey: "driveLength")
UserDefaults.standard.set(noOfBenoBagsInputText.text, forKey: "noOfBenoBags")
UserDefaults.standard.set(weightOfBenoBagInputText.text, forKey: "weightOfBenoBag")
UserDefaults.standard.set(benoQtyForTanksInputText.text, forKey: "benoQtyForTanks")
UserDefaults.standard.set(noOfBenoBagsPerPalletInputText.text, forKey: "benoBagsPerPallet")
}
// Adding toolbar to top of keyboard with "Done" button (toolbar.swift file)
override func viewDidLoad() {
super.viewDidLoad()
machineODInputText.inputAccessoryView = toolBar()
pipeODInputText.inputAccessoryView = toolBar()
pipeLengthInputText.inputAccessoryView = toolBar()
driveLengthInputText.inputAccessoryView = toolBar()
muckUpInputText.inputAccessoryView = toolBar()
jackingSpeedInputText.inputAccessoryView = toolBar()
weightOfBenoBagInputText.inputAccessoryView = toolBar()
noOfBenoBagsInputText.inputAccessoryView = toolBar()
benoQtyForTanksInputText.inputAccessoryView = toolBar()
noOfBenoBagsPerPalletInputText.inputAccessoryView = toolBar()
}
// load old data into input feilds
override func viewDidAppear(_ animated: Bool) {
if let a = UserDefaults.standard.object(forKey: "TBMOD") as? String {
machineODInputText.text = a
}
if let a = UserDefaults.standard.object(forKey: "pipeOD") as? String {
pipeODInputText.text = a
}
if let a = UserDefaults.standard.object(forKey: "muckUp") as? String {
muckUpInputText.text = a
}
if let a = UserDefaults.standard.object(forKey: "speed") as? String {
jackingSpeedInputText.text = a
}
if let a = UserDefaults.standard.object(forKey: "pipeLength") as? String {
pipeLengthInputText.text = a
}
if let a = UserDefaults.standard.object(forKey: "driveLength") as? String {
driveLengthInputText.text = a
}
if let a = UserDefaults.standard.object(forKey: "noOfBenoBags") as? String {
noOfBenoBagsInputText.text = a
}
if let a = UserDefaults.standard.object(forKey: "weightOfBenoBag") as? String {
weightOfBenoBagInputText.text = a
}
if let a = UserDefaults.standard.object(forKey: "benoQtyForTanks") as? String {
benoQtyForTanksInputText.text = a
}
if let a = UserDefaults.standard.object(forKey: "benoBagsPerPallet") as? String {
noOfBenoBagsPerPalletInputText.text = a
}
// load dark/light mode last selected by user
let mode = UserDefaults.standard.string(forKey: "mode")
if mode == "dark" {
overrideUserInterfaceStyle = .dark
} else {
overrideUserInterfaceStyle = .light
}
machineODInputText.clearsOnBeginEditing = true
pipeODInputText.clearsOnBeginEditing = true
pipeLengthInputText.clearsOnBeginEditing = true
driveLengthInputText.clearsOnBeginEditing = true
muckUpInputText.clearsOnBeginEditing = true
jackingSpeedInputText.clearsOnBeginEditing = true
weightOfBenoBagInputText.clearsOnBeginEditing = true
noOfBenoBagsInputText.clearsOnBeginEditing = true
benoQtyForTanksInputText.clearsOnBeginEditing = true
noOfBenoBagsPerPalletInputText.clearsOnBeginEditing = true
}
}

Answer 1

you can save it in UserDefaults as follows.
#IBAction func darkButton(_ sender: Any) {
overrideUserInterfaceStyle = .dark
UserDefaults.standard.set("dark", forKey: "mode")
}
#IBAction func lightButton(_ sender: Any) {
overrideUserInterfaceStyle = .light
UserDefaults.standard.set("light", forKey: "mode")
}
When reopening the application do as follow.
let mode = UserDefaults.standard.string(forKey: "mode")
if mode == "dark" {
overrideUserInterfaceStyle = .dark
} else {
overrideUserInterfaceStyle = .light
}
Where you need to add the above code depends on your scenario. I suggest to add it inside AppDelegate -> didFinishLaunchingWithOptions.