How to initialize derived variables in body methods in SwiftUI (or alternate approach) - binding

Question

I'm trying to figure out the right way to initialized derived variables in the body method for a SwiftUI view. An example would the string value for an editable integer which would then be edited in a TextField. The integer could for example be part of an #ObservedObject. I cannot figure out any remotely clean way to do this.
I've looked into using custom initializers but this does not seem like the right thing to do. I'm not even sure this code would be run at the appropriate time.
I've also tried using the .onAppear method for TextField, but this method does not appear to be re-executed when the view is rebuilt.
simplified example:
final class Values : ObservableObject {
#Published var count: Int = 0;
}
var sharedValues = Values()
struct ContentView : View {
#ObservedObject var values = sharedValues
var body: some View {
VStack {
Button(
action: { self.add() },
label: { Text("Plus")}
)
InnerView()
}
}
func add() { values.count += 1 }
}
struct InnerView : View {
#ObservedObject var values = sharedValues
#State private var text = ""
var body: some View {
// text = String(value.count) - what I want to do
TextField("", text: $text, onEditingChanged: updateCount)
.textFieldStyle(RoundedBorderTextFieldStyle())
}
func updateCount(updated: Bool) { /* this isn't important in this context */}
}
I would hope to be able to update sharedValues externally and see the update in MyView. In this example, I would want pressing the button to update the text field with the updated text value. But I can't figure a way to have the string representation of the count value computed at the appropriate point in the execution of the code.
I've tried multiple approaches to achieving this type of result, but have come up short.

Answer 1

I'm not sure if I'm understanding your question correctly, but if you are just trying to be able to change a number with a button, have the number be displayed in a text field, and then be able to edit it there, you don't need an ObserverableObject or multiple views.
Here is an example of how you can do it:
struct ContentView: View {
#State var count = 0
#State var countStr = ""
var body: some View {
VStack {
Button(action: {
self.count += 1
self.countStr = "\(self.count)"
}) {
Text("Plus")
}
TextField("", text: $countStr, onEditingChanged: updateCount)
}
}
func updateCount(updated: Bool) { /* this isn't important in this context */ }
}

Answer 2

Use value init method of TextField. This take the value as 2 way Binding. So it automatically update count from both text field and buttons.
import SwiftUI
import Combine
final class Values : ObservableObject {
#Published var count: Int = 0;
}
var sharedValues = Values()
struct AndrewVoelkel : View {
#ObservedObject var values = sharedValues
var body: some View {
HStack {
InnerView()
VStack{
Button(
action: { self.add() },
label: { Text("+")}
)
Button(
action: { self.sub() },
label: { Text("-")}
)
}.font(.headline)
}.padding()
}
func add() { values.count += 1 }
func sub() { values.count -= 1 }
}
struct InnerView : View {
#ObservedObject var values = sharedValues
var body: some View {
TextField("", value: $values.count, formatter: NumberFormatter())
.textFieldStyle(RoundedBorderTextFieldStyle())
}
}