Updating EnvironmentObject Variable by Assignment in Button - swiftui

Question

I have a throwaway project I am using to try to familiarize myself with SwiftUI. Essentially, I have various types of apples, that I have made available through an EnvironmentObject variable. The project parallels the Landmarks tutorial that I have been through, but I am expanding on the use of objects such as steppers and buttons, etc.
I am currently attempting to have a button, when pressed, save the UUID of a certain variety of apple and send it back to the original view. It is not working, and I am not sure why. It seems like a problem of the environmentObject assignment not escaping the closure for the action:. Have have set print statements and Text views to display the values of the variables at certain points. While it seems to set the variable in the closure, it doesn't escape the closure and the variable is never really updated.
func scene(
_ scene: UIScene,
willConnectTo session: UISceneSession,
options connectionOptions: UIScene.ConnectionOptions
) {
if let windowScene = scene as? UIWindowScene {
let window = UIWindow(windowScene: windowScene)
window.rootViewController = UIHostingController(rootView: ContentView().environmentObject(UserData()))
self.window = window
window.makeKeyAndVisible()
}
}
struct AppleData: Codable, Hashable, Identifiable {
let id: UUID
var appleType: String
var numberOfBaskets: Int
var numberOfApplesPerBasket: [Int]
var fresh: Bool
static let `default` = Self(id: UUID(uuidString: "71190FD1-C8E0-4A65-996E-9CE84D200FBA")!,
appleType: "appleType",
numberOfBaskets: 1,
numberOfApplesPerBasket: [0],
fresh: true) // for purposes of automatic preview
func image(forSize size: Int) -> Image {
ImageStore.shared.image(name: appleType, size: size)
}
}
let appleData: [AppleData] = load("apples.json")
var appleUUID: UUID?
func load<T: Decodable>(_ filename: String, as type: T.Type = T.self) -> T {
... // Code Omitted For Brevity
}
final class UserData: ObservableObject {
let willChange = PassthroughSubject<UserData, Never>()
var apples = appleData {
didSet {
willChange.send(self)
}
}
var appleId = appleUUID {
didSet {
willChange.send(self)
}
}
}
struct ContentView : View {
#EnvironmentObject private var userData: UserData
var body: some View {
NavigationView {
List {
ForEach(appleData) { apple in
NavigationLink(
destination: AppleDetailHost(apple: apple).environmentObject(self.userData)
) {
Text(verbatim: apple.appleType)
}
}
Text("self.userData.appleId: \(self.userData.appleId?.uuidString ?? "Nil")")
}
... // Code Omitted For Brevity
}
}
struct AppleDetail : View {
#EnvironmentObject var userData: UserData
#State private var basketIndex: Int = 0
var apple: AppleData
var totalApples: Int {
apple.numberOfApplesPerBasket.reduce(0, +)
}
var body: some View {
VStack {
... // Code Omitted For Brevity
}
Button(action: {
print("self.userData.appleId: \(self.userData.appleId?.uuidString ?? "Nil")")
self.userData.appleId = self.apple.id
print("self.userData.appleId: \(self.userData.appleId?.uuidString ?? "Nil")")
}) {
Text("Use Apple")
}
Text("self.apple.id: \(self.apple.id.uuidString)")
Text("self.userData.appleId: \(self.userData.appleId?.uuidString ?? "Nil")")
}
... // Code Omitted For Brevity
}
The output of the print statements in the Button in AppleDetail is:
self.userData.appleId: Nil
self.userData.appleId: 28EE7739-5E5A-4CA4-AFF5-7A6BFE025250
The Text view that shows self.userData.appleId in ContentView is always Nil. Any help would be greatly appreciated.

Answer 1

In beta 5, the ObservableObject no longer uses willChange. It uses objectWillChange instead. In addition, it also autosynthesizes the subject, so you do not have to write it yourself (although you could overwrite it if you want).
On top of that, there's a new property wrapper (#Published), that will make changes on a property to have the publisher emit. No need to manually call .send(), as it will be done automatically. So if in your code, you rewrite your UserData class like this, it will work fine:
final class UserData: ObservableObject {
#Published var apples = appleData
#Published var appleId = appleUUID
}