SwiftUI sheet dimension turns into 0 when altering theme (iOS 16 bug?)

I am caught with a bizarre SwiftUI bug. I’ve a sheet that is presupposed to dimension itself based mostly on its content material (utilizing PreferenceKey + GeometryReader). Every little thing works positive till I attempt to change the consumer interface type utilizing overrideUserInterfaceStyle.

Once I change the theme like this, the sheet dimension immediately turns into 0 and onPreferenceChange is not even referred to as. This solely occurs on iOS 16.

You’ll be able to see the issue within the display screen recordings.

iOS 16.4
iOS 18.1

import SwiftUI

fileprivate struct IntrinsicContentSizePreferenceKey: PreferenceKey {
    static let defaultValue: CGSize = .zero
    
    static func scale back(worth: inout CGSize, nextValue: () -> CGSize) {
        worth = nextValue()
    }
}

fileprivate struct FittedPresentationDetentModifier: ViewModifier {
    @State non-public var contentSize: CGSize = .zero

    func physique(content material: Content material) -> some View {
        content material
            .overlay(
                GeometryReader { proxy in
                    Shade.clear.choice(
                        key: IntrinsicContentSizePreferenceKey.self,
                        worth: proxy.dimension
                    )
                }
            )
            .onPreferenceChange(IntrinsicContentSizePreferenceKey.self) { newSize in
                print("→ present dimension: (contentSize)")
                print("→ new dimension: (newSize)")
                guard newSize != .zero else { return }
                contentSize = newSize
            }
            .presentationDetents([.height(contentSize.height)])
            .presentationCornerRadius(32.0)
    }
}

fileprivate extension View {
    func fittedPresentationDetent() -> some View {
        modifier(FittedPresentationDetentModifier())
    }
}

extension View {
    func bottomSheet<Content material: View>(
        isPresented: Binding<Bool>,
        @ViewBuilder content material: @escaping () -> Content material
    ) -> some View {
        self.sheet(isPresented: isPresented) {
            content material()
                .fittedPresentationDetent()
        }
    }
}

i created a pattern mission for testing.

import SwiftUI

struct ContentView: View {
    @State non-public var showSheet = false
    @Setting(.colorScheme) var colorScheme
    
    var isDarkMode: Bool {
        colorScheme == .darkish
    }
    
    var physique: some View {
        NavigationView {
            VStack(spacing: 20) {
                Picture(systemName: isDarkMode ? "moon.fill" : "solar.max.fill")
                    .font(.system(dimension: 60))
                    .foregroundColor(isDarkMode ? .white : .yellow)
                    .padding()
                
                Textual content("Present Theme: (isDarkMode ? "Darkish" : "Gentle")")
                    .font(.headline)
                
                Button(motion: {
                    showSheet.toggle()
                }) {
                    Textual content("Change Theme")
                        .font(.headline)
                        .padding()
                        .background(Shade.blue)
                        .foregroundColor(.white)
                        .cornerRadius(10)
                }
            }
            .navigationTitle("Theme Switcher")
            .bottomSheet(isPresented: $showSheet, content material: {
                ThemeSettingsSheet(isDarkMode: isDarkMode)
            })
        }
    }
}

struct ThemeSettingsSheet: View {
    let isDarkMode: Bool
    @Setting(.dismiss) var dismiss
    
    var physique: some View {
        Toggle(isOn: Binding(
            get: { isDarkMode },
            set: { newValue in
                changeTheme(isDarkMode: newValue)
            }
        )) {
            HStack {
                Picture(systemName: isDarkMode ? "moon.fill" : "solar.max.fill")
                    .foregroundColor(isDarkMode ? .white : .yellow)
                Textual content("Darkish Mode")
            }
        }
        .padding()
    }
    
    non-public func changeTheme(isDarkMode: Bool) {
        guard let windowScene = UIApplication.shared.connectedScenes.first as? UIWindowScene,
              let window = windowScene.home windows.first else { return }
        
        UIView.transition(with: window,
                          length: 0.3,
                          choices: .transitionCrossDissolve,
                          animations: {
            window.overrideUserInterfaceStyle = isDarkMode ? .darkish : .gentle
        }, completion: nil)
    }
}

#Preview {
    ContentView()
}

Anybody run into this? Any workarounds? Thanks!