Calculate equation in Swift

Hello every one i am fairly new to Swift and I have an app where I need to get a users input and put it into an equation to show on a different view controller. Im having trouble entering this equation as follows...

masterMix.waterVolumeLabel.text = numberOfSamplesTextField(50 - dNTPsVolumeLabel.text - forwardPrimerLabel.text - reversePrimerLabel.text - dnaPolymeraseLabel.text - volumeOfTemplateDNAtextfield.text - masterMix.bufferVolumeLabel)

The total from inside the parentheses need to be multiplied by numberOfSamplesTextField

How would i write this in swift? The equation is inside prepare for segue.

import UIKit
class SelectAttributesViewController: UIViewController, UIPickerViewDelegate, UIPickerViewDataSource, UITextFieldDelegate {
@IBOutlet weak var kitPickerView: UIPickerView!
@IBOutlet weak var reactionVolumeLabel: UILabel!
@IBOutlet weak var numberOfSampleTextField: UITextField!
@IBOutlet weak var volumeOfTemplateDNATextField: UITextField!
@IBOutlet weak var slider: UISlider!
@IBOutlet weak var calculateButton: UIButton!
let kits = ["kit 1", "Kit 2"]
let pArray = [10,20,50]
override func viewDidLoad() {
super.viewDidLoad()
self.numberOfSampleTextField.delegate = self
self.volumeOfTemplateDNATextField.delegate = self
kitPickerView.dataSource = self
kitPickerView.delegate = self
//slider.addTarget(self, action: "reactionVolumeSlider", for: .valueChanged)
let tap = UITapGestureRecognizer(target: self.view, action: #selector(UIView.endEditing(_:)))
view.addGestureRecognizer(tap)
// Do any additional setup after loading the view.
}
func pInterval() {
slider.minimumValue = 0
slider.maximumValue = Float(pArray.count)
slider.isContinuous = false
}
@IBAction func reactionVolumeSlider(_ sender: UISlider) {
print(Int(sender.value))
let currentValue = pArray[Int(sender.value)]
reactionVolumeLabel.text = "\(currentValue) μL"
}
func numberOfComponents(in pickerView: UIPickerView) -> Int {
return 1
}
func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
return kits.count
}
func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
if row == 0{ print(kits[row])
}else if row == 1{
createAlert(title: "Kit not available", message: "More kits will be added soon!")
calculateButton.isEnabled = false
}
}
func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
return kits[row]
}
func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
guard let oldText = textField.text, let r = Range(range, in: oldText) else {
return true
}
let newText = oldText.replacingCharacters(in: r, with: string)
let isNumeric = newText.isEmpty || (Double(newText) != nil)
let numberOfDots = newText.components(separatedBy: ".").count - 1
let numberOfDecimalDigits: Int
if let dotIndex = newText.firstIndex(of: ".") {
numberOfDecimalDigits = newText.distance(from: dotIndex, to: newText.endIndex) - 1
} else {
numberOfDecimalDigits = 0
}
return isNumeric && numberOfDots <= 1 && numberOfDecimalDigits <= 2
}
func createAlert (title: String, message: String){
let alert = UIAlertController(title: title, message: message, preferredStyle: UIAlertController.Style.alert)
alert.addAction(UIAlertAction(title: "Ok", style: UIAlertAction.Style.default, handler: { (Action) in
alert.dismiss(animated: true, completion: nil)
}))
self.present(alert, animated: true, completion: nil)
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
let masterMix = segue.destination as! MasterMixTableViewController
masterMix.loadViewIfNeeded()
// The line below is where I tried to implement this function
// masterMix.waterVolumeLabel!.text = 
masterMix.bufferVolumeLabel.text = String(Double(numberOfSampleTextField.text!)! * 10)
masterMix.dNTPsVolumeLabel.text = numberOfSampleTextField!.text // done
masterMix.forwardPrimerLabel.text = String(Double(numberOfSampleTextField.text!)! * 2.5) //done
masterMix.reversePrimerLabel.text = String(Double(numberOfSampleTextField.text!)! * 2.5) //done
masterMix.dnaPolymeraseLabel.text = String(Double(numberOfSampleTextField.text!)! * 0.5) //done
//answer.text = String(Int(entry.text)! * 2)
}
@IBAction func calculatePressed(_ sender: Any) {
if numberOfSampleTextField.text != ""{
performSegue(withIdentifier: "masterMixSegue", sender: self)
}
}
}

There's some issues with what you're trying to do. First you shouldn't be setting the content of a view in your destination view controller in prepareForSegue. You can calculate the value, and then pass it as Phillip suggested. First you'll have to calculate it. One other issue is that you can't run mathematical operators on text, which is what it looks like you're trying to do. You can cast a String into an Int or a Double, and it will return as optional just in case the text doesn't actually contain a number. It would be safest to always conditionally unwrap, but I think for your case you could do something like add an extension on String to return either the non-optional double value of the text, or zero if it's nil (that way it wouldn't have any impact on the result). So add this to your project outside of any classes:

extension String {
func doubleValue() -> Double {
return Double(self) ?? 0
}
}

Now in your first VC, you can add this function below to do your calculation. I'm going to assume that you left some code out, because in the code you provided you haven't declared a lot of these different labels and textFields (dNTPsVolumeLabel, forwardPrimerLabel, etc). So assuming you already have those as a part of your first VC, something like this should work fine:

func getWaterVolumeLabelText() -> String? {
numberOfSamplesTextField.text?.doubleValue() * (50.0 - dNTPsVolumeLabel.text?.doubleValue() - forwardPrimerLabel.text?.doubleValue() - reversePrimerLabel.text?.doubleValue() - dnaPolymeraseLabel.text?.doubleValue() - volumeOfTemplateDNAtextfield.text?.doubleValue() - bufferVolumeLabel.text?.doubleValue())
}

Now you have a function that will run your calculation for you when the segue is fired. All you have to do is pass it to the destination ViewController. The easiest way to do this would be to just add a string property in your destination view controller, something like this:

class MasterMixTableViewController: UIViewController{
// This is would be your label in your destination view controller
@IBOutlet weak var waterVolumeLabel: UILabel!
// Add this
public var waterVolumeText: String?
override func viewWillAppear(_ animated: Bool) {
// Here you can do whatever with the passed-in string
waterVolumeLabel.text = waterVolumeText
}
}

Now go back to the prepare for segue method in your SelectAttributesViewController and just change it to this:

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
let masterMix = segue.destination as! MasterMixTableViewController
masterMix.loadViewIfNeeded()
// This will pass the value along
masterMix.waterVolumeText = getWaterVolumeLabelText()
}