Hello, I've a question about performance when trying to render lots of items coming from SwiftData via a @Query on a SwiftUI List. Here's my setup:
// Item.swift:
@Model final class Item: Identifiable {
var timestamp: Date
var isOptionA: Bool
init() {
self.timestamp = Date()
self.isOptionA = Bool.random()
}
}
// Menu.swift
enum Menu: String, CaseIterable, Hashable, Identifiable {
var id: String { rawValue }
case optionA
case optionB
case all
var predicate: Predicate<Item> {
switch self {
case .optionA: return #Predicate { $0.isOptionA }
case .optionB: return #Predicate { !$0.isOptionA }
case .all: return #Predicate { _ in true }
}
}
}
// SlowData.swift
@main
struct SlowDataApp: App {
var sharedModelContainer: ModelContainer = {
let schema = Schema([Item.self])
let modelConfiguration = ModelConfiguration(schema: schema, isStoredInMemoryOnly: false)
return try! ModelContainer(for: schema, configurations: [modelConfiguration])
}()
var body: some Scene {
WindowGroup {
ContentView()
}
.modelContainer(sharedModelContainer)
}
}
// ContentView.swift
struct ContentView: View {
@Environment(\.modelContext) private var modelContext
@State var selection: Menu? = .optionA
var body: some View {
NavigationSplitView {
List(Menu.allCases, selection: $selection) { menu in
Text(menu.rawValue).tag(menu)
}
} detail: {
DemoListView(selectedMenu: $selection)
}.onAppear {
// Do this just once
// (0..<15_000).forEach { index in
// let item = Item()
// modelContext.insert(item)
// }
}
}
}
// DemoListView.swift
struct DemoListView: View {
@Binding var selectedMenu: Menu?
@Query private var items: [Item]
init(selectedMenu: Binding<Menu?>) {
self._selectedMenu = selectedMenu
self._items = Query(filter: selectedMenu.wrappedValue?.predicate,
sort: \.timestamp)
}
var body: some View {
// Option 1: touching `items` = slow!
List(items) { item in
Text(item.timestamp.description)
}
// Option 2: Not touching `items` = fast!
// List {
// Text("Not accessing `items` here")
// }
.navigationTitle(selectedMenu?.rawValue ?? "N/A")
}
}
When I use Option 1 on DemoListView, there's a noticeable delay on the navigation. If I use Option 2, there's none. This happens both on Debug builds and Release builds, just FYI because on Xcode 16 Debug builds seem to be slower than expected: https://indieweb.social/@curtclifton/113273571392595819
I've profiled it and the SwiftData fetches seem blazing fast, the Hang occurs when accessing the items property from the List. Is there anything I'm overlooking or it's just as fast as it can be right now?
