Why is it in SwiftUI, when presenting modal view with .sheet, init() is called twice

Question

I am producing the situation on WatchOS with the following code

struct Modal : View {
    @Binding var showingModal : Bool
    
    init(showingModal : Binding<Bool>){
        self._showingModal = showingModal
        print("init modal")
    }
    
    var body: some View {
        Button(action: {
            self.showingModal.toggle()
        }, label: {
            Text("TTTT")
        })
    }
}

struct ContentView: View {
    @State var showingModal = false
    var body: some View {
        Button(action: {
            self.showingModal.toggle()
        }, label: {
            Text("AAAA")
        }).sheet(isPresented: $showingModal, content: {Modal(showingModal: self.$showingModal)})
    }
}

Every time I press the button in the master view to summon the modal with .sheet, Two instances of the modal view are created.

Could someone explain this phenomenon?

Answer 1

I tracked this down in my code to having the following line in my View:

@Environment(\.presentationMode) var presentation

I had been doing it due to https://stackoverflow.com/a/61311279/155186, but for some reason that problem seems to have disappeared for me so I guess I no longer need it.

I've filed Feedback FB7723767 with Apple about this.

Answer 2

It is probably a bug, as of Xcode 11.4.1 (11E503a). Beware, that if for example initializing view models (or anything else for that matter) like so:

.sheet(isPresented: $isEditingModalPresented) {
    LEditView(vm: LEditViewModel(), isPresented: self.$isEditingModalPresented)
}

the VM will be initialized twice.