Swift passing calculated data back to previous view controller - ios

Question

I am creating my first simple budgeting app. Basically, I take a few user inputs like monthly income & savings goal. Then they click "start", & the app calculates stuff such as, their daily budget etc.
Here I'm running into trouble. After all the calculations, I display "how much you can spend each day" (e.g. $20 a day), which I pass forward through segues from their original inputs on the original screen.
Now, in this VC (UserInfoVC) I created a button which lets them add how much money they spent today. So when they click this "add money spent" button, I open a new VC (AddSubtractMoney) where I present a calculator where they can enter how much they spent today (i.e. $12) and click submit.
I run their input compared to their daily budget to get a New daily budget.
Now, I'm having trouble passing this updated number backwards, to display it on the previous VC on the label "dailySpendingLimitLabel". I know segues are not the best way to go about passing data backwards.
I've tried closures, but I end up getting lost in the syntax, and protocols and delegates (it's my 2nd month coding).
Is there a simple way to achieve passing this data back to the previous VC and populating the data in that previous display label?
Below is the code.
The First snippet is from the UserInfoVC where I display their originally entered data that I segued through. The Second snippet is from the AddSubtractMoney class where I placed the calculator and created an object "newestUpdate" inside a function that allows me to calculate the number they entered on the calculator minus their old daily budget. To arrive at a new budget which I want to present backwards to the UserInfoVC.
class UserInfoViewController : ViewController {
var userNamePassedOver : String?
var userDailyBudgetPassedOver : Double = 99.0
var userDailySavingsPassedOver : Double = 778.00
var userMonthlyEarningsPassedOver : Double?
var userDesiredSavingsPassedOver : Double?
var newAmountPassedBack : Double = 0.0
#IBOutlet weak var dailySavingsNumberLabel: UILabel!
#IBOutlet weak var userNameLabel: UILabel!
#IBOutlet weak var dailySpendingLimitLabel: UILabel!
override func viewDidLoad() {
super.viewDidLoad()
userNameLabel.text = userNamePassedOver
dailySpendingLimitLabel.text = String(format: "%.2f", userDailyBudgetPassedOver)
dailySavingsNumberLabel.text = String(format: "%.2f", userDailySavingsPassedOver)
}
#IBAction func addSubtractMoneyPressed(_ sender: UIButton) {
performSegue(withIdentifier: "addOrSubtractMoney", sender: self)
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == "addOrSubtractMoney"{
let addOrSubtractMoneyVC = segue.destination as! AddSubtractMoney
addOrSubtractMoneyVC.dailyBudgetPassedThrough = userDailyBudgetPassedOver
}
}
}
extension UserInfoViewController: AddSubtractMoneyDelegate {
func calculatedValue(value: Double) {
dailySpendingLimitLabel.text = String(userDailyBudgetPassedOver - value)
}
}
import UIKit
protocol AddSubtractMoneyDelegate {
func calculatedValue(value: Double)
}
class AddSubtractMoney: UIViewController {
#IBOutlet weak var outputLabel: UILabel!
var runningNumber = ""
var finalNumberPassedOver : Double?
var amountPassedBackToUserInfo : Double = 0.0
var dailyBudgetPassedThrough : Double = 0.0
var delegate: AddSubtractMoneyDelegate?
override func viewDidLoad() {
super.viewDidLoad()
outputLabel.text = "0"
// Do any additional setup after loading the view.
}
#IBAction func buttonPressed(_ sender: UIButton) {
runningNumber += "\(sender.tag)"
outputLabel.text = runningNumber
}
#IBAction func submitNewInfo(_ sender: UIButton) {
// FIX FIX
AddSubtractMoneyController.addToMoneySpentArray(amountISpent: outputLabel.text!)
sendBackUpdatedNumber()
dismiss(animated: true, completion: nil)
}
#IBAction func allClearedPressed(_ sender: UIButton) {
runningNumber = ""
outputLabel.text = "0"
}
// THIS LINE PRODUCES THE CORRECT INPUT IN OUTPUT CONSOLE WHEN I PRINT- BUT I CANT FIGURE HOW TO TRANSFER IT BACK TO PREVIOUS VC
func sendBackUpdatedNumber(){
let newestUpdate = UserInfo(whatYouSpentToday: runningNumber, oldDailyBudgetPassed: dailyBudgetPassedThrough)
amountPassedBackToUserInfo = dailyBudgetPassedThrough - Double(runningNumber)!
newestUpdate.goalToSaveDaily = amountPassedBackToUserInfo
print(amountPassedBackToUserInfo)
self.delegate?.calculatedValue(value: amountPassedBackToUserInfo)
}
}

Answer 1

My suggestion is to use a callback closure. It's less code and easier to handle than protocol / delegate.
In AddSubtractMoney declare a callback variable and call it in sendBackUpdatedNumber passing the Double value
class AddSubtractMoney: UIViewController {
// ...
var callback : ((Double)->())?
// ...
func sendBackUpdatedNumber(){
let newestUpdate = UserInfo(whatYouSpentToday: runningNumber, oldDailyBudgetPassed: dailyBudgetPassedThrough)
amountPassedBackToUserInfo = dailyBudgetPassedThrough - Double(runningNumber)!
newestUpdate.goalToSaveDaily = amountPassedBackToUserInfo
print(amountPassedBackToUserInfo)
callback?(amountPassedBackToUserInfo)
}
}
In prepare(for segue assign the closure to the callback variable and add the code to be executed on return
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == "addOrSubtractMoney"{
let addOrSubtractMoneyVC = segue.destination as! AddSubtractMoney
addOrSubtractMoneyVC.callback = { result in
print(result)
// do something with the result
}
addOrSubtractMoneyVC.dailyBudgetPassedThrough = userDailyBudgetPassedOver
}
}

Answer 2

Using delegate
if segue.identifier == "addOrSubtractMoney" {
let addOrSubtractMoneyVC = segue.destination as! AddSubtractMoney
addOrSubtractMoneyVC.dailyBudgetPassedThrough = userDailyBudgetPassedOver
addOrSubtractMoneyVC.delegate = self
}
}
You need to add delegate property in AddSubtractMoney class
var delegate: AddSubtractMoneyDelegate?
Create Protocol in AddSubtractMoney class
protocol AddSubtractMoneyDelegate {
func calculatedValue(value: Double)
}
And respond to delegate
func sendBackUpdatedNumber(){
let newestUpdate = UserInfo(whatYouSpentToday: runningNumber, oldDailyBudgetPassed: dailyBudgetPassedThrough)
amountPassedBackToUserInfo = dailyBudgetPassedThrough - Double(runningNumber)!
newestUpdate.goalToSaveDaily = amountPassedBackToUserInfo
print(amountPassedBackToUserInfo)
self.delegate.calculatedValue(value: amountPassedBackToUserInfo)
}
Now you need to implement this delegate method in class where delegate is set.
Here in UserInfoViewController class delegate is set so you need to implement its delegate method
extension UserInfoViewController: AddSubtractMoneyDelegate {
func calculatedValue(value: Double) {
//set label here
}
}

Answer 3

You could possibly also use an unwind segue to pass back the data.

Answer 4

If you don't under stand flow behind delegate(protocol oriented), you can simply go through below code. it only works if both class
But it is not a good practice
Learn about protocol, closure, or Notification Center broadcasting for mostly used, flexible and reusable coding methods.
UserInfoViewController
class UserInfoViewController : ViewController {
fun receiveBackUpdatedNumber(numberString:String){
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == "addOrSubtractMoney"{
let addOrSubtractMoneyVC = segue.destination as! AddSubtractMoney
addOrSubtractMoneyVC.userInfoViewController = self
}
}
}
}
AddSubtractMoney
class AddSubtractMoney: UIViewController {
var userInfoViewController: UserInfoViewController!
var updatedNumber = ""
func sendBackUpdatedNumber(){
self.userInfoViewController.receiveBackUpdatedNumber(numberString: updatedNumber)
}
}
If you are confirtable you can go with protocols.. protocols insist a class to compulsory implement a method, which make code more reusable and independent.
In Above method we are passing instance of current viewcontroller(UserInfoViewController) to next viewcontroller(AddSubtractMoney) on performing segue, So by that we can access any properties of function in UserInfoViewController from AddSubtractMoney. So it make easy to pass data from AddSubtractMoney to -> UserInfoViewController