Open Radar

 
Sometimes we face issues with LazyVStack and ScrollView on SwiftUI and the view gets completely blank out of nowhere. It stays like that until I do a tiny swipe to scroll, then the view re-appears. I notice that more often with "taller" views inside the LazyVStack.

I see this issue happening on many different scenarios. It was hard to isolate but I could get a reliable way to reproduce it.

You will notice that I'm using an "id" modifier there and also a "lineSpacing" modifier. They are not really needed to trigger the bug as I could see it happening even without it, but they make the bug to trigger easily. The bug in the example will trigger after tapping the bottom Add button sometimes, but I've seeing it to trigger even when just scrolling through the scroll view and without the id and lineSpacing modifier:

struct MyDataStruct: Identifiable {
  var id = UUID()
  var otherId = UUID()
  var text: String
}

struct ContentView: View {
  @State var contents = (0..<10).map { _ in
    MyDataStruct(
      text: (0..<40)
        .map { "looooong row \($0) long row block\n" }
        .reduce("", +)
    )
  }
  var body: some View {
    ScrollView {
      LazyVStack {
        ForEach(contents) { content in
          VStack {
            Text(content.text)
              .lineSpacing(30)
              .id(content.otherId)
          }
        }
        Button {
          contents.append(MyDataStruct(text: "X"))
          contents.remove(at: 0)
        } label: {
          Text("Add")
        }
      }
    }
  }
}