SwiftUI Lifecycle on macOS: present new scene with its own viewmodel

Question

I have a macOS app which I'd like to open several instances of in separate windows. For demonstration purposes, I have this tiny example project here:

import SwiftUI @main struct MultipleWindowsApp: App { var body: some Scene { WindowGroup { MyView() .environmentObject(ViewModel()) .frame(minWidth: 200, minHeight: 200) } } } struct MyView: View { @EnvironmentObject var vm: ViewModel var body: some View { Toggle(isOn: $vm.toggleState, label: { Text("Some Toggle") }) } } class ViewModel: ObservableObject { @Published var toggleState = false }

As it is, a new window created from the menu bar will have a reference to the same ViewModel instance (toggling in one window toggles the other and vice versa). I failed to find a simple answer on how I can have different windows with their own respective viewmodels (please note: I am not handling documents here that need to get saved etc., I am just consuming and visualising an api in my app).

Asperi · Accepted Answer · 2021-01-18 15:45:41Z

Here is a snapshot of Apple API documentation

/// Every window created from the group maintains independent state. For /// example, for each new window created from the group the system allocates new /// storage for any ``State`` or ``StateObject`` variables instantiated by the /// scene's view hierarchy. /// /// You typically use a window group for the main interface of an app that isn't /// document-based. For document-based apps, use a ``DocumentGroup`` instead. @available(iOS 14.0, macOS 11.0, tvOS 14.0, watchOS 7.0, *) public struct WindowGroup<Content> : Scene where Content : View {

so, try the following (cannot test now):

@main struct MultipleWindowsApp: App { var body: some Scene { WindowGroup { MyView() .frame(minWidth: 200, minHeight: 200) } } } struct MyView: View { @StateObject var vm = ViewModel() // << this one !! var body: some View { Toggle(isOn: $vm.toggleState, label: { Text("Some Toggle") }) } }

Awesome, exactly, what I was missing, thanks. So I guess if in my real application I want to use the viewmodel instance as an EnvironmentObject, I just inject it one level lower (in this example in MyView). Very helpful, as always!
I got to this solution as well. The issue is you can’t use commands for your app in macOS when you want to use the model.

Collectives™ on Stack Overflow

SwiftUI Lifecycle on macOS: present new scene with its own viewmodel

1 Answer 1

2 Comments

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Related