Purple warning – “Publishing changes”

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)
	}
	}

view raw habitView.swift hosted with ❤ by GitHub