How to refresh a View?

Have a look here: https://developer.apple.com/tutorials/swiftui/creating-a-watchos-app

At step 4 they show how to create a state var to do this.

@main
struct LandmarksApp: App {
  @StateObject private var modelData = ModelData()

   var body: some Scene
      WindowGroup {
        ContentView()
       •environmentObject(modelData)
     }
  }
}

Thanks, but in their Landmarks example the modelData is only ever set once: ModelData.swift:12 = @Published var landmarks: [Landmark] = load("landmarkData.json"). I need to update the data in that model so that it can be used in the content views.

Let's say I have a singleton, and the delegate calls the singleton's methods when it receives data. So:

• The iOS app sends new data to the Watch.
• The Watch delegate receives the new data.
• The delegate calls a method in the singleton to store the information in the group defaults.
• That data is not yet available to the modelData.

How do I get that new data into the modelData?

final class ModelData : ObservableObject {
	@Published var items: [ItemDetail] = getItems()
}

class WatchAppSingleton {
	@EnvironmentObject var modelData: ModelData
...

At this point I can access what's in the modelData, but not write to it.

If I try something like modelData.items = <some new items> Xcode tells me: No ObservableObject of type ModelData found. A View.environmentObject(_:) for ModelData may be missing as an ancestor of this.

Does the line @Published var items: [ItemDetail] = getItems() execute once or multiple times? How do I get it to grab the data again?

I can't be the only person who needs to update the data in their model? Am I just doing it wrong?!

Ah, right, got it...

This:

class WatchAppSingleton {
	@EnvironmentObject var modelData: ModelData

should be this:

class WatchAppSingleton {
    @StateObject var modelData: ModelData = ModelData()

An error message more like this would be great; modelData is marked as an @EnvironmentObject. Did you mean @StateObject?

For anyone coming across this thread, here's how I got it to work. It might not be 100% correct, but it's definitely working here.

Background:

• iOS app in Objective-C with a SwiftUI Watch extension ("Watch App").
• Watch App has a delegate ("WatchAppDelegate") conforming to WKApplicationDelegate and WCSessionDelegate.
• WatchConnectivity session delegate methods are in the WatchAppDelegate.
• WatchAppDelegate also contains my ModelData class. This contains some @Published vars that other Views can see, and will refresh when those values change. The class is also an @ObservableObject.

WatchAppDelegate.swift

// Instantiate the model data here, *once only*. This is your single source of truth.
let modelData: ModelData = ModelData()

class ModelData : ObservableObject {
	@Published var availableItems: [ItemDetail] = defaultsGetAvailableItems() // Gets an array of ItemDetail from the defaults
	@Published var mainItem: ItemDetail = defaultsGetMainItem() // Again, from the defaults
}

class WatchAppDelegate : NSObject, WKApplicationDelegate, WCSessionDelegate, ObservableObject {
	var session: WCSession?
	override init() {
		super.init()
		if(WCSession.isSupported()) {
			if(session == nil) {
				session = WCSession.default // Start the Watch Connectivity session
				session!.delegate = self
				session!.activate()
			}
		}
	}
    // Delegate methods go here, session didReceiveMessage etc.
    ...
}

When the WCSession delegate methods are called and triggered in WatchAppDelegate, the delegate deals with the new data that's come in. So, for example, the iOS app has just sent a message dictionary with, maybe: "newItems" : arrayOfNewItems. The delegate takes those new items and stores them in the defaults.

At that point, you also update the modelData: modelData.availableItems = defaultsGetAvailableItems() and modelData.mainItem = defaultsGetMainItem(). Your one source of truth has been updated with the new data.

Okay, the WatchApp is the @main entry point into the app, and you need to start the delegate in there:

WatchApp.swift

@main
struct WatchApp: App {
	@WKApplicationDelegateAdaptor private var appDelegate: WatchAppDelegate // Launches the delegate, which creates the modelData instance
	var body: some Scene {
		WindowGroup {
			AppContentView(modelData: modelData)
				.environmentObject(modelData) // Give access to modelData to the receiving view (probably, I dunno, but it's necessary)
		}
	}
}

struct AppContentView : View {
	@ObservedObject var modelData: ModelData
	var body: some View {
		VStack {
			if(modelData.availableitems.count == 0) { // If there are no items, display an appropriate view and message
				NoItemsView()
						.environmentObject(modelData)
				} else { // We have items
					ItemsListView()
						.environmentObject(modelData)
				}
...
}

ItemsListView.swift

struct ItemsListView: View {
	@EnvironmentObject var modelData: ModelData // To access the data
    var body: some View {
		VStack {
			NavigationView {
				List {
					// List of items
					ForEach(modelData.availableItems) { item in
						NavigationLink {
							ItemDetailView(item: item)
						} label: {
							TableRowView(item: item)
						}
					}
				}
			}
		}
    }
}

ItemDetailView.swift

struct ItemDetailView: View {
	@EnvironmentObject var modelData: ModelData
	var event: ItemDetail

  // This lets us access the particular item in the array by its index
	var itemIndex: Int {
		modelData.availableItems.firstIndex(where: { $0.id == item.id })!
	}

	var body: some View {
...

Happy to be told what I've done is wrong or bad or bad practice or whatever, but it's working right now...!