Purple warning - "Publishing changes"

Fri, 21 Oct 2022 00:00:00 +0000

It’s a pretty safe bet that if Xcode is saying there’s an error in my code, that it’s correct, and I am in error - not Xcode. Today I came across a situation where that might not be true.

I think the purple warnings are problems detected at runtime - I’ve heard of thread problems causing purple warnings. The error I was getting was “Publishing changes from within view updates is not allowed, this will cause undefined behavior.”

The error was on two lines in my model where I’d called a method to update the model from a button press in a sub-view function.

After poking around to try and work it out, I found this clear blog post from Donny Wals and it turns out it’s possibly a bug in XCode 14. My situation fitted the description - calling the method from a button in a list, and the temporary workaround of adding a modifier to the button eliminated the warning.

I’m on Xcode 14.0, and I gather from Donny’s post that the problem might have been fixed in newer versions.

Here’s the calling code - a button in a list, with the “fix” on line 25.

 func habitView(habitItem: HabitItem, habitsCollection: Habits) -> some View {
 HStack {
 VStack(alignment: .leading) {
 Text(habitItem.name)
 .font(.headline)
 Text(habitItem.lastDone.formatted(date: .abbreviated, time: .omitted))
 }
 Text(" (\(habitItem.timesDone))")
 .font(.largeTitle)
 Spacer()
 Button {
 if !habitsCollection.markAsDone(habit: habitItem) {
 print("Unexpected error - habit not found in collection:\(habitItem.name)")
 }
 } label: {
 if habitItem.due {
 Image(systemName: "rectangle")
 .font(.system(size: 40))
 } else {
 Image(systemName: "checkmark.rectangle")
 .font(.system(size: 40))
 }

 }
 .buttonStyle(.bordered)
 }
 }

Bug on blog.iankulin.com

Purple warning - "Publishing changes"