Swiftui Using a calculated value from 1 view in another view - view

Question

I am relatively new to Swiftui and am currently working on my second App which is much more complex that the first.
I have hit a wall on one particular requirement which I have been trying to resolve for a few days now and I am now going round in circles having used numerous videos and articles about State/Binding/ObservableObject etc.
I am developing a scoring App for Golf where the user will go through each hole in turn and enter their scores, various calculations will be done and displayed in the view. One of them is the total points scored. When they move onto the second hole the same process will be followed but there is one additional calculation which requires to add together the total points from Hole 1 and Hole 2. The various methods I have tried have either ended up in a value of 0 or more error messages that I care to remember and certainly too many to include in here!!
I would appreciate any help, I have included my code below (cut down for the purpose of this post) including some notes to explain what I need to do which I hope are clear. If anyone can adapt my code to something that works that would be great as I can then see how it all fits together.
Thanks in advance
START VIEW
// This screen is simply used to start a round. It will take you to Hole 1 and from there the navigationlink in Hole 1 will take you to Hole 2 and so on.
import SwiftUI
struct ContentView: View {
var body: some View {
NavigationView {
NavigationLink(destination: Hole1View()) {
Text("Start Round")
.frame(width: 300, height: 30)
.font(.system(size: 18, weight: .bold, design: .rounded))
.lineLimit(1)
.multilineTextAlignment(.center)
.padding(18)
.background(Color.yellow)
.foregroundColor(Color.blue)
.cornerRadius(10)
.border(Color.blue, width: 10)
.cornerRadius(1)
}
}
}
}
struct ContentView_Previews : PreviewProvider {
static var previews: some View {
ContentView()
}
}
HOLE 1 VIEW
// On this view you will enter various information and there will be various calculations to include in the View. One of the calculations is to calculate a value (Hole1totalpoints) which will be required in calculations in the next view.
import SwiftUI
struct Hole1View: View {
#State private var hole1gross = 0
var hole1totalpoints: Int {
let hole1points = hole1gross * 3
return hole1points
}
var body: some View {
// On this view you will enter various information and there will be various calculations to include in the View. One of the calculations is to calculate a value (Hole1totalpoints) which will be required in calculations in the next view.
Stepper("\(hole1gross)", value: $hole1gross, in: 0...15)
.frame(width: 300, height: 35, alignment: .leading)
.font(.system(size: 16, weight: .bold, design: .rounded))
.minimumScaleFactor(0.6)
.multilineTextAlignment(.leading)
.lineLimit(2)
Text("Calculated Value \(hole1totalpoints)")
NavigationLink(destination: Hole2View()) {
Text("Go to hole 2")
}
}
}
struct Hole1View_Previews: PreviewProvider {
static var previews: some View {
Hole1View()
}
}
HOLE 2 VIEW
// On this view you will enter various information and there will be various calculations to include in the View. One of the calculations is to calculate a value (Hole2totalpoints). One of the calculations needs to include the value hole1totalpoints from the previous view (Hole1View) to calculate the total points from the 2 views (hole1totalpoints+hole2totalpoints) which can be used in the View.
import SwiftUI
struct Hole2View: View {
#State private var hole2gross = 0
#State private var hole2totpoints = 0
var hole2totalpoints: Int {
let hole1points = hole2gross * 2
return hole1points
}
var body: some View {
Stepper("\(hole2gross)", value: $hole2gross, in: 0...15)
.frame(width: 300, height: 35, alignment: .leading)
.font(.system(size: 16, weight: .bold, design: .rounded))
.minimumScaleFactor(0.6)
.multilineTextAlignment(.leading)
.lineLimit(2)
Text("Calculated Value \(hole2totalpoints)")
}
}
struct Hole2View_Previews: PreviewProvider {
static var previews: some View {
Hole2View()
}
}

Answer 1

You can accomplish this with #ObservableObject or an #EnvironmentObject. I've chosen to show it here with passing an #ObservableObject via props, but you could easily change this to just injecting my ScoreManager object at the top with environmentObject as well:
struct ContentView: View {
#ObservedObject var scoreManager = ScoreManager()
var body: some View {
NavigationView {
NavigationLink(destination: Hole1View(scoreManager: scoreManager)) {
Text("Start Round")
.frame(width: 300, height: 30)
.font(.system(size: 18, weight: .bold, design: .rounded))
.lineLimit(1)
.multilineTextAlignment(.center)
.padding(18)
.background(Color.yellow)
.foregroundColor(Color.blue)
.cornerRadius(10)
.border(Color.blue, width: 10)
.cornerRadius(1)
}
}
}
}
class ScoreManager : ObservableObject {
#Published var hole1gross = 0
var hole1totalpoints: Int {
let hole1points = hole1gross * 3
return hole1points
}
#Published var hole2gross = 0
#Published var hole2totpoints = 0
var hole2totalpoints: Int {
//do any calculations here relating to hole 1 points, since you have access to both
let hole1points = hole2gross * 2
return hole1points
}
var hole1AndHole2Points : Int {
hole1totalpoints + hole2totalpoints
}
}
struct Hole1View: View {
#ObservedObject var scoreManager : ScoreManager
var body: some View {
Stepper("\(scoreManager.hole1gross)", value: $scoreManager.hole1gross, in: 0...15)
.frame(width: 300, height: 35, alignment: .leading)
.font(.system(size: 16, weight: .bold, design: .rounded))
.minimumScaleFactor(0.6)
.multilineTextAlignment(.leading)
.lineLimit(2)
Text("Calculated Value \(scoreManager.hole1totalpoints)")
NavigationLink(destination: Hole2View(scoreManager: scoreManager)) {
Text("Go to hole 2")
}
}
}
struct Hole2View: View {
#ObservedObject var scoreManager : ScoreManager
var body: some View {
Stepper("\(scoreManager.hole2gross)", value: $scoreManager.hole2gross, in: 0...15)
.frame(width: 300, height: 35, alignment: .leading)
.font(.system(size: 16, weight: .bold, design: .rounded))
.minimumScaleFactor(0.6)
.multilineTextAlignment(.leading)
.lineLimit(2)
Text("Calculated Value \(scoreManager.hole2totalpoints)")
Text("Both holes: \(scoreManager.hole1AndHole2Points)")
}
}
ContentView now creates a ScoreManager. It gets passed down through the other views in the NavigationLinks. The other views end up with the same version of that object (it isn't getting recreated in the new views -- they all have the same reference to the original). Then, in the original, you have access to all the scores you want. I created hole1AndHole2Points which I think does what you're describing. You can see the value reflected in the last Text item on Hole 2.
If you wanted to go the environment object route, the code will be very similar. More reading on that system: https://www.hackingwithswift.com/quick-start/swiftui/how-to-use-environmentobject-to-share-data-between-views