Swiftui how to update variable once view is closed - swiftui

Question

I am using SwiftUi 3.0 and I am new to it . I am learning about ObservedObjects . What I am trying to do is update the count of a variable every time that I close a view . This is the entire small app . The screen starts at DataUpdateView view when I click Next View I go to DataUpdateView2 view . Once I close DataUpdateView2 and go back to the original view I want to have the
Text("Score Count \(progress.score)")
score number increase by 1 since in the second view I do a +1 every time that I close that view . Any suggestions would be great
import SwiftUI
class UserProgress: ObservableObject {
#Published var score = 0
}
struct DataUpdateView: View {
#State var nextView = false
#StateObject var progress = UserProgress()
var body: some View {
VStack {
Text("Score Count \(progress.score)")
Text("Next View")
.onTapGesture {
nextView = true
}.fullScreenCover(isPresented: $nextView, content: {
DataUpdateView2()
})
}
}
}
struct DataUpdateView_Previews: PreviewProvider {
static var previews: some View {
DataUpdateView()
}
}
struct DataUpdateView2: View {
#ObservedObject var progress = UserProgress()
#Environment(\.presentationMode) var presentationMode
var body: some View {
Text("Back")
.onTapGesture {
progress.score += 1
self.presentationMode.wrappedValue.dismiss()
}
}
}
struct DataUpdateView2_Previews: PreviewProvider {
static var previews: some View {
DataUpdateView2()
}
}

Answer 1

You're probably not seeing the first view update since both views are instantiating their own UserProgress(). You need to pass the object you already created in the first view along to the second in the initializer
So In DataUpdateView:
.fullScreenCover(isPresented: $nextView, content: {
DataUpdateView2(progress: progress)
})
}
And then in DataUpdateView2:
struct DataUpdateView2: View {
#ObservedObject var progress: UserProgress
#Environment(\.presentationMode) var presentationMode
// ...
}
So now the second view is receiving the object from the first rather than creating its own.

Answer 2

Note: If you are not using an ObservableObject, then take a look at the second part.
In this specific situation, you don't even need a Binding variable, you can just use the .onDisappear method. .onDisappear Documentation.
import SwiftUI
class UserProgress: ObservableObject {
#Published var score = 0
}
struct DataUpdateView: View {
#State var nextView = false
#StateObject var progress = UserProgress()
var body: some View {
VStack {
Text("Score Count \(progress.score)")
Text("Next View")
.onTapGesture {
nextView = true
}.fullScreenCover(isPresented: $nextView, content: {
DataUpdateView2()
})
}
}
}
struct DataUpdateView_Previews: PreviewProvider {
static var previews: some View {
DataUpdateView()
}
}
struct DataUpdateView2: View {
#ObservedObject var progress = UserProgress()
#Environment(\.presentationMode) var presentationMode
var body: some View {
Text("Back")
.onTapGesture{
presentationMode.wrappedValue.dismiss()
print("Dismissed!")
}
.onDisappear{
//This is called when the view disappears.
progress.score += 1
}
}
}
struct DataUpdateView2_Previews: PreviewProvider {
static var previews: some View {
DataUpdateView2()
}
}
Second Part
If you want the variable to update when the view closes, you could use the .onDisappear method and a Binding value. An example implementation of this is below:
struct ViewOne: View{
#State var number = 0
var body: some View{
VStack{
Text("Number: \(number)")
NavigationLink(destination: ViewTwo(variable: $number)){
Text("Go To View Two")
}
}
}
}
struct ViewTwo: View{
#Binding var variable: Int
var body: some View{
//Content of view 2 here
Text("View Two")
.onDisappear{
//This is called when the view disappears
variable += 1
}
}
}

Answer 3

In short you need to use same view model in both views. A possible and seems simplest approach in your code is to inject view model from first view to second via environment object, like
#StateObject var progress = UserProgress()
var body: some View {
VStack {
Text("Score Count \(progress.score)")
Text("Next View")
.onTapGesture {
nextView = true
}.fullScreenCover(isPresented: $nextView, content: {
DataUpdateView2()
.environmentObject(progress) // << here !!
})
and use it internally, like
struct DataUpdateView2: View {
#EnvironmentObject var progress: UserProgress // << injected automatically !!