Updating .sheet size at runtime in SwiftUI

gistfile1.swift

import SwiftUI

extension PresentationDetent {
    static let small = PresentationDetent.height(200)
}

struct Item: Identifiable, Hashable {
    let title: String

    var id: String { title }
}

let data: [Item] = [
    .init(title: "Hello"),
    .init(title: "world"),
]

struct SheetContentDetailView: View {
    let item: Item
    let onDismiss: () -> Void

    var body: some View {
        VStack {
            Button(action: { onDismiss() }, label: {
                Text("Close")
            })

            HStack {
                Text("Title:")
                Text(item.title)
                    .font(.title)
            }
        }
    }
}

struct SheetContentListView: View {
    @Binding var selectedItem: Item?

    @State var selection: Item?

    var body: some View {
        List(data, id: \.self, selection: $selection) { item in
            VStack(alignment: .leading) {
                Text(item.title)
                    .font(.headline)
                    .foregroundStyle(.primary)
                Text("Subtitle")
                    .font(.subheadline)
                    .foregroundStyle(.secondary)
            }.tint(.primary)
        }
        .onChange(of: selection) { oldValue, newValue in
            withAnimation {
                selectedItem = selection
            }
        }
    }
}

struct SheetView: View {
    @Binding var isPresented: Bool
    @Binding var selectedDetent: PresentationDetent

    @State var detailItem: Item?

    var body: some View {
        if let detailItem {
            SheetContentDetailView(
                item: detailItem,
                onDismiss: {
                    self.detailItem = nil
                    selectedDetent = .small
                }
            )
            .transition(.push(from: .bottom))
            .onAppear {
                if selectedDetent == .small {
//                    selectedDetent = .medium
                }
            }
        } else {
            SheetContentListView(selectedItem: $detailItem)
        }
    }
}

struct ContentView: View {
    @State private var isShowingSheet = false

    @State var currentDetent: PresentationDetent = .small

    var body: some View {
        VStack {
            Button("Show Sheet") {
                isShowingSheet = true
            }
        }
        .sheet(
            isPresented: $isShowingSheet,
            onDismiss: {
                currentDetent = .medium
            }
        ) {
            SheetView(
                isPresented: $isShowingSheet,
                selectedDetent: $currentDetent
            )
            .presentationDetents([.medium, .small], selection: $currentDetent)
            .presentationBackgroundInteraction(.enabled)
        }
    }
}

#Preview {
    ContentView()
}