iPhone Duo 开发者适配：SwiftUI 按窗口宽度选界面框架

import SwiftUI
 
enum ShellLayout {
    static func usesSplit(horizontalSizeClass: UserInterfaceSizeClass?) -> Bool {
        UIDevice.current.userInterfaceIdiom == .pad || horizontalSizeClass == .regular
    }
}

struct RootView: View {
    @Environment(\.horizontalSizeClass) private var horizontalSizeClass
    @State private var shellSelection = ShellSelection()
 
    var body: some View {
        Group {
            if ShellLayout.usesSplit(horizontalSizeClass: horizontalSizeClass) {
                PadRootView()      // 带侧边栏的 NavigationSplitView
            } else {
                MainTabView()      // 标签栏
            }
        }
        .environment(shellSelection)
    }
}

import Observation
 
@Observable
final class ShellSelection {
    var section: String?
}

struct MainTabView: View {
    @Environment(ShellSelection.self) private var shell: ShellSelection?
    @State private var selection: AppTab = .today
 
    var body: some View {
        content
            .onAppear(perform: restoreSection)
            .onChange(of: selection) { _, new in shell?.section = new.rawValue }
    }
 
    private func restoreSection() {
        guard let raw = shell?.section else { return }
        // "日记本"这类分区在标签栏里没有，就回到"今天"
        selection = AppTab(rawValue: raw) ?? .today
    }
}

.toolbar(UIDevice.current.userInterfaceIdiom == .pad ? .automatic : .hidden, for: .navigationBar)

private struct SplitShellKey: EnvironmentKey {
    static let defaultValue = false
}
 
extension EnvironmentValues {
    var isSplitShell: Bool {
        get { self[SplitShellKey.self] }
        set { self[SplitShellKey.self] = newValue }
    }
}
 
// 在 PadRootView 中：
NavigationSplitView { sidebar } detail: {
    detail(for: selection)
        .environment(\.isSplitShell, true)
}
 
// 在页面中：
@Environment(\.isSplitShell) private var isSplitShell
// ...
.toolbar(isSplitShell ? .automatic : .hidden, for: .navigationBar)

#if DEBUG
static func applyOrientationFlag() {
    let args = CommandLine.arguments
    guard let i = args.firstIndex(of: "-orientation"), i + 1 < args.count else { return }
    for (step, name) in args[i + 1].split(separator: ",").enumerated() {
        let mask: UIInterfaceOrientationMask = name == "portrait" ? .portrait : .landscapeRight
        DispatchQueue.main.asyncAfter(deadline: .now() + Double(step + 1) * 4) {
            for scene in UIApplication.shared.connectedScenes.compactMap({ $0 as? UIWindowScene }) {
                scene.requestGeometryUpdate(.iOS(interfaceOrientations: mask))
            }
        }
    }
}
#endif