Passing one StateObject class of one view to another StateObject class of a different view in SwiftUI - class

Question

I have two views each with their own class. The first view has an #StateObject of class "DataClass" that initializes a simple struct DataStruct:
struct View1 : View {
#StateObject var dataToPass = DataClass()
var body: some View {
NavigationView{
ZStack{
NavigationLink(destination: View2(data: dataToPass)){
Text("Navigation Link to View2")
}
}
}
}
}
struct dataStruct {
var variable1 : String
var variable2 : String
}
class DataClass : ObservableObject {
var data : dataStruct
init(){
data = dataStruct(variable1: "1", variable2: "2")
}
}
I'm trying to keep this same instance of the DataClass/dataStruct and pass it on to View2 and its View2Class:
struct View2: View {
#ObservedObject var data : DataClass
#StateObject var game = View2Class(data: data)
var body: some View {
Text("Hello")
}
}
class View2Class : ObservableObject {
#ObservedObject var data : DataClass
init(data : DataClass){
self.data = data
}
}
I want it so that there is only ever one instance/initialization of dataStruct and thus dataClass and View2Class has access to it. View2Class must remain a StateObject. As of right now I am getting an error on the declaration of View2's StateObject: "Cannot use instance member 'data' within property initializer; property initializers run before 'self' is available."
I'm sure it is an easy conceptual fix that I am not understanding right now. Thank you!

Answer 1

To fix the error ("Cannot use instance member 'data'...") try something like this:
struct View1 : View {
#StateObject var dataToPass = DataClass()
var body: some View {
NavigationView{
ZStack{
NavigationLink(destination: View2(data: dataToPass, game: View2Class(data: dataToPass))){
Text("Navigation Link to View2")
}
}
}
}
}
// ...
struct View2: View {
#ObservedObject var data: DataClass
#StateObject var game: View2Class
var body: some View {
Text("Hello")
}
}

Answer 2

You cannot use data to declare game, because data is not "available" before View2 is setup. That is the reason you get the error.
Try this approach, using #Published in the ObservableObject classes,
and passing DataStruct from DataClass to your View2Class with a function in
.onAppear {...}:
struct DataStruct {
var variable1: String
var variable2: String
}
class DataClass: ObservableObject {
#Published var data = DataStruct(variable1: "1", variable2: "2")
}
struct View2: View {
#ObservedObject var dataClass: DataClass
#StateObject var game = View2Class()
var body: some View {
Text("Hello")
.onAppear {
game.setData(dataClass.data)
}
}
}
class View2Class: ObservableObject {
#Published var data: DataStruct?
func setData(_ data: DataStruct){
self.data = data
}
}

Answer 3

#StateObject is used to declare a source of truth with a lifetime automatically tied to a view that requires reference type semantics (i.e. needs to perform tasks other than simply holding data where #State would be more suitable). It doesn't make sense to pass data into one because it is no longer a source of truth because it now has a dependency on another object - the problem is the object doesn't know when the data being passed in has changed (Which SwiftUI supports natively with its View struct and body method). I would suggest redesigning your data flow to be more SwiftUI compatible, there are some great WWDC data flow talks like this one.