presentedWindowStyle is not windowStyle

This post is mostly to herald a pretty good Apple bug report response, which as we know is a too-rare event. But it might also help others with this confusing SwiftUI API.

What’s the difference between presentedWindowStyle(_:) and windowStyle(_:)?

Well, one does something, the other doesn’t, basically.

I tried using the former, and observed that it never has any effect. I filed FB14892608 about it, a month ago. While the long delay isn’t great, the response I got today was actually pretty helpful:

We’re sorry you ran into trouble with that API.

To adjust the style of a window group’s windows, you have a couple of options. If all of the windows in the group should have the same style, then using the windowStyle() scene modifier is what you want:

struct MyApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
        }
        .windowStyle(.hiddenTitleBar)
    }
}

If you need to adjust the style on an individual basis using state for that window, there are also some related view modifiers:
struct MyApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
                .toolbar(removing: .title)
                .toolbarBackgroundVisibility(.hidden, for: .windowToolbar)
        }
    }
}

A simple apology followed by clear and specific instructions on how to actually achieve what I wanted. I genuinely applaud Apple – or perhaps I should more specifically thank the individual(s) within DTS that actually provided this response. Either way, it was a very pleasant surprise.

---

Now, it still leaves unanswered the question of what presentedWindowStyle(_:) is supposed to be for, and in what situations it actually does anything. So not a perfect reply, per se, but really the proper solution for that is either:

1. Fix the API to not have such confusingly similar modifiers.
2. Improve the documentation to:
   • Explicitly point out the other, similarly-named modifier.
   • Distinguish them.

Currently the documentation is just:

Sets the style for windows created by this scene.

windowStyle(_:) documentation

Versus:

Sets the style for windows created by interacting with this view.

presentedWindowStyle(_:) documentation

The latter might technically convey something important here, in the created by interacting with this view part, but so much in SwiftUI is modifiers stuck haphazardly in weird and arbitrary places, that I’m been conditioned to ignore the fact that I’m often applying modifiers to views that don’t actually affect those views. And for all I know in SwiftUI parlance views do “create” and/or “interact” with their parent windows (a lot about SwiftUI is backwards, part of its nature as a declarative API).

Especially if that’s the first candidate API you stumble across, when searching for a way to style a window, it’s very easy to presume it’s the right API. Why would there be multiple APIs for styling the window; why would you continue searching after finding one?

Similarly, the presentedWindowStyle(_:) variant is the only one that appears in Xcode’s auto-complete if you try to add the modifier to your main view, which is both where you sometimes have to add window-level modifiers and also just a really easy mistake to make (instead of adding the modifier to the WindowGroup, one indentation level up).

Lastly, it doesn’t help that I can’t find any situation in which presentedWindowStyle(_:) has any effect, even knowing it’s not intended to style the parent window. One might assume it’s somehow related to sheets or somesuch, but apparently not? Presumably I’m overlooking some use-case – or maybe it doesn’t actually do anything on macOS, only iDevices? I welcome clues or tips.