iPhone Duo App Resizability

import SwiftUI

struct RootView: View {
    @Environment(\.horizontalSizeClass) private var horizontalSizeClass
    @Environment(\.verticalSizeClass) private var verticalSizeClass

    private var isUnfoldedRegular: Bool {
        horizontalSizeClass == .regular && verticalSizeClass == .regular
    }

    var body: some View {
        Group {
            if isUnfoldedRegular {
                // Inner display, unfolded: take advantage of the extra width
                NavigationSplitView {
                    ConversationListView()
                } detail: {
                    ConversationDetailView()
                }
            } else {
                // Outer display, or folded: behave like a standard iPhone
                NavigationStack {
                    ConversationListView()
                }
            }
        }
        // Asymmetric insets around the hinge and camera housings are
        // applied automatically — don't hardcode padding here.
        .safeAreaPadding(.horizontal)
    }
}

struct ConversationListView: View {
    var body: some View { Text("Conversations") }
}

struct ConversationDetailView: View {
    var body: some View { Text("Select a conversation") }
}