macOS Settings UI with Liquid Glass

This skill produces a native macOS settings window that follows Apple's macOS 26 design guidelines. The result is a sidebar + detail NavigationSplitView with liquid glass window chrome, back/forward toolbar navigation, grouped Form sections with transparent backgrounds, and proper scroll edge effects.

Architecture Overview

The settings UI is composed of 3 layers:

1. Window Controller (SettingsWindowController.swift) — An NSWindowController that creates the NSWindow programmatically with .fullSizeContentView. This is what gives the window rounded liquid glass corners. You cannot get this effect from a SwiftUI Window scene.
2. Root View (SettingsView.swift) — A NavigationSplitView with a sidebar list and detail pane. Includes back/forward navigation history in the toolbar, which also forces the creation of an NSToolbar (required for the liquid glass title bar treatment).
3. Detail Panes (one file per tab) — Each pane uses Form { Section(...) { ... } }.formStyle(.grouped).scrollContentBackground(.hidden).

Why NSWindowController Instead of SwiftUI Window Scene

SwiftUI's declarative Window scene does not expose the NSWindow style mask. The .fullSizeContentView flag must be set at window creation time for macOS 26 to render the liquid glass chrome (rounded corners, translucent sidebar, blurred title bar). Trying to inject it later via NSViewRepresentable is unreliable because SwiftUI resets the window's configuration.

The NSWindowController approach also lets you control the toolbar style, frame autosave, minimum size, and delegate lifecycle directly.

Critical Modifiers

Every detail pane MUST have these three modifiers on its Form:

.formStyle(.grouped)
.scrollContentBackground(.hidden)
.contentMargins(.top, 8, for: .scrollContent)

• .formStyle(.grouped) — gives the native inset rounded-rect section appearance
• .scrollContentBackground(.hidden) — makes the form background transparent so the liquid glass window chrome shows through. Without this, you get an opaque white/dark background that breaks the glass effect.
• .contentMargins(.top, 8) — adds breathing room between the toolbar and the first section

The sidebar List MUST have:

.listStyle(.sidebar)
.scrollEdgeEffectStyleSoftIfAvailable()  // macOS 26 progressive blur at scroll edges
.navigationTitle("Settings")

The NavigationSplitView MUST have:

NavigationSplitView(columnVisibility: .constant(.all))  // sidebar always visible
// ...
.navigationTitle("Settings")
.navigationSplitViewStyle(.balanced)

Reference Implementation

Read the reference files for complete, working code:

• references/SettingsWindowController.swift — The window controller (copy as-is, adapt the activation policy calls to your app)
• references/SettingsView.swift — The root view with sidebar, detail routing, and navigation history
• references/ExampleDetailPane.swift — A template detail pane showing common control patterns (Toggle, Picker, Slider, LabeledContent)

Step-by-Step: Adding Settings to a New App

1. Create the Tab Enum

Define your settings categories. Each case needs a title and SF Symbol icon:

enum SettingsTab: String, CaseIterable, Identifiable {
    case general
    case appearance
    case about

    var id: Self { self }

    var title: String {
        switch self {
        case .general: "General"
        case .appearance: "Appearance"
        case .about: "About"
        }
    }

    var systemImage: String {
        switch self {
        case .general: "gearshape"
        case .appearance: "paintbrush"
        case .about: "info.circle"
        }
    }
}

2. Create the Window Controller

Copy references/SettingsWindowController.swift into your project. Adapt:

• The initial contentRect size (default 700x540 is good for most apps)
• The minSize (default 620x460)
• The activation policy calls (AppActivationPolicy.enter()/leave()) — if your app isn't a menu-bar-only app, remove these

3. Create the Root Settings View

Copy references/SettingsView.swift. Adapt:

• The SettingsTab enum cases to match your categories
• The SettingsDetailView switch to return your panes

4. Create Detail Panes

For each tab, create a pane file. Use this template:

import SwiftUI

struct GeneralSettingsPane: View {
    @AppStorage("someKey") private var someValue = false

    var body: some View {
        Form {
            Section("Section Name") {
                Toggle("Toggle label", isOn: $someValue)
            }
        }
        .formStyle(.grouped)
        .scrollContentBackground(.hidden)
        .contentMargins(.top, 8, for: .scrollContent)
    }
}

5. Open Settings from Your App

From a menu bar, button, or anywhere:

SettingsWindowController.show(tab: .general)

Do NOT use a SwiftUI Window scene. Do NOT use openWindow(id:). The window controller handles everything.

6. Remove Any SwiftUI Window Scene

If you previously had a Window("Settings", id: "SETTINGS") scene in your App struct, remove it entirely. The SettingsWindowController replaces it.

Common Control Patterns Inside Form Sections

Toggle with description:

Toggle(isOn: $value) {
    VStack(alignment: .leading, spacing: 2) {
        Text("Primary label")
        Text("Description text explaining what this does.")
            .font(.caption)
            .foregroundStyle(.secondary)
    }
}
.toggleStyle(.switch)

Picker (dropdown):

Picker("Label", selection: $value) {
    Text("Option A").tag(OptionEnum.a)
    Text("Option B").tag(OptionEnum.b)
}
.pickerStyle(.menu)

Picker (segmented):

Picker("Label", selection: $value) {
    ForEach(SomeEnum.allCases) { item in
        Text(item.title).tag(item)
    }
}
.pickerStyle(.segmented)

Slider with value label:

LabeledContent("Size") {
    HStack(spacing: 12) {
        Slider(value: $size, in: 24...96, step: 2)
            .frame(width: 180)
        Text("\(Int(size)) pt")
            .monospacedDigit()
            .foregroundStyle(.secondary)
            .frame(width: 46, alignment: .trailing)
    }
}

Button row:

HStack(spacing: 8) {
    Button("Action") { doSomething() }
        .controlSize(.small)
    Button("Reset") { reset() }
        .controlSize(.small)
        .disabled(isDefault)
}

Menu-Bar-Only Apps

If your app uses NSApp.setActivationPolicy(.accessory) (no Dock icon), you need activation policy management so the settings window brings the app to the foreground. The reference SettingsWindowController calls AppActivationPolicy.enter() on show and .leave() on close. Implement this as a simple reference-counting wrapper:

@MainActor
enum AppActivationPolicy {
    private static var count = 0

    static func enter() {
        count += 1
        NSApp.setActivationPolicy(.regular)
        NSApp.activate(ignoringOtherApps: true)
    }

    static func leave() {
        count = max(0, count - 1)
        guard count == 0 else { return }
        Task { @MainActor in
            NSApp.setActivationPolicy(.accessory)
        }
    }
}

If your app always shows in the Dock, remove the AppActivationPolicy calls from the window controller and just use NSApp.activate(ignoringOtherApps: true) in showWindow.

macOS Version Compatibility

The scrollEdgeEffectStyle(.soft) API is macOS 26+ only. Always wrap it in an availability check:

private extension View {
    @ViewBuilder
    func scrollEdgeEffectStyleSoftIfAvailable() -> some View {
        if #available(macOS 26.0, *) {
            scrollEdgeEffectStyle(.soft, for: .all)
        } else {
            self
        }
    }
}

The rest of the pattern (NSWindowController with .fullSizeContentView, grouped Form, NavigationSplitView) works on macOS 14+.