I'm experiencing a significant UI freeze in my SwiftUI app that uses SwiftData with CloudKit sync. When users tap a button to present a sheet for the first time after app launch, the entire UI becomes unresponsive for 5-10 seconds. Subsequent sheet presentations work fine.
App Architecture
Service layer: An @Observable class marked with @MainActor that orchestrates operations
Persistence layer: A @ModelActor class that handles SwiftData operations
SwiftUI views: Using @Environment to access the service layer
The structure looks like this:
@Observable
@MainActor
final class MyServices {
let persistence: DataPersistence
init(modelContainer: ModelContainer) {
self.persistence = DataPersistence(modelContainer: modelContainer)
}
func addItem(title: String) async {
// Creates and saves an item through persistence layer
}
}
@ModelActor
actor DataPersistence {
func saveItem(_ item: Item) async {
// Save to SwiftData
}
}
The app initializes the ModelContainer at the Scene level and passes it through the environment:
@main
struct MyApp: App {
let container = ModelContainer(for: Item.self)
var body: some Scene {
WindowGroup {
ContentView()
.modelContainer(container)
.environment(MyServices(modelContainer: container))
}
}
}
The Problem
When a user taps the "Add Item" button which presents a sheet:
Button("Add Item") {
showingAddSheet = true
}
.sheet(isPresented: $showingAddSheet) {
AddItemView(onAdd: { title in
await services.addItem(title: title)
})
}
The UI freezes completely for 5-10 seconds on first presentation. During this time:
The button remains in pressed state
No UI interactions work
The app appears completely frozen
After the freeze, the sheet opens and everything works normally
This only happens on the first sheet presentation after app launch. I suspect it's related to SwiftData's ModelContext initialization happening on the main thread despite using @ModelActor, but I'm not sure why this would happen given that ModelActor should handle background execution.
Environment
iOS 18
SwiftData with CloudKit sync enabled
Xcode 16
Swift 6
Has anyone experienced similar freezes with SwiftData and @ModelActor? Is there something wrong with how I'm structuring the initialization of these components? The documentation suggests @ModelActor should handle background operations automatically, but the freeze suggests otherwise.
Any insights would be greatly appreciated!
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