jank-scrolling.swift

import SwiftUI

struct ContentView: View {
  let items = [0, 1, 2, 3, 4]

  @State private var position = ScrollPosition(idType: Int.self)
  @State private var showPage: Bool = true

  let height = 300.0
  let width = 300.0

  var body: some View {
    NavigationStack {
      VStack {
        Text("This scrolls nicely.")
        Text("It's at the navigation root.")

        demoView

        Spacer()

        Button(action: {
          showPage = true
        }) {
          Text("Go to broken version")
        }
        .buttonStyle(.bordered)
        .navigationDestination(isPresented: $showPage) {
          VStack {
            Text("This studders when scrolling.")
            Text("It's in a navigationDestination.")

            demoView

            Spacer()
          }
        }

        Spacer()
      }
    }
  }

  @ViewBuilder var demoView: some View {
    let _ = Self._printChanges()

    ScrollView(.vertical) {
      LazyVStack(spacing: 0) {
        ForEach(items, id: \.self) { _ in
          Text("Scroll me")
            .frame(width: width, height: height)
            .border(.pink)
        }
      }
      .scrollTargetLayout()
    }
    .frame(width: width, height: height)
    .border(.blue)
    .scrollPosition($position)
  }
}

#Preview {
  ContentView()
    .modelContainer(for: Item.self, inMemory: true)
}