SwiftUI Sheet Crash with Occasional Warning about Modifying State - macos

Question

I have a SwiftUI button that, when clicked, a sheet displays a confirmation modal. When a button is clicked in that modal to confirm, I make a save to Core Data.
I'm getting one or all of a few nasty results:
The sheet just hangs and becomes unresponsive.
I get a warning: "Modifying state during view update, this will cause undefined behavior".
I get a crash.
Obviously I'm modifying the state becomes I'm deleting a thing, but I'm unclear on how to do this right.
Here is my view where I click delete:
struct MyView: View{
#State var showDeleteModal = false
var body: some View{
Button("Delete"){
showDeleteModal.toggle()
}
.sheet(isPresented: self.$showDeleteModal) {
ModalView(confirm: {
self.showDeleteModal.toggle()
//Save the object in my Core Data stuff
model.saveThing(thing: thing)
})
}
}
}
And here's my modal that has a callback function to confirm the deletion:
struct ModalView: View {
var confirm:() -> Void
var body: some View {
Button("Confirm"){
confirm()
}
}
}
How do I hide the modal and make the save (which removes the view from the screen) without interfering with SwiftUI's state?

Answer 1

I'd suggest using sheet(isPresented:onDismiss:content:) and calling model.saveThing in onDismiss:
struct MyView: View {
#State var showDeleteModal = false
var body: some View {
Button("Delete") {
showDeleteModal.toggle()
}
.sheet(isPresented: self.$showDeleteModal, onDismiss: onDismiss) {
ModalView()
}
}
func onDismiss() {
model.saveThing(thing: thing)
}
}
Then you can dismiss the sheet without knowing the parent's state - just use #Environment(\.presentationMode):
struct ModalView: View {
#Environment(\.presentationMode) private var presentationMode
var body: some View {
Button("Confirm") {
presentationMode.wrappedValue.dismiss()
}
}
}
Note: as sheet can be closed without interacting with the confirm button, you can detect how it was closed using another #State variable - see:
SwiftUI: How to show an alert after a sheet is closed?