I'm using SwiftData to persist my items in storage. I used .modelContext
to pass in my shared context, and on iOS 18 (both on a physical device and a simulator), I discovered a bug where SwiftData doesn't automatically save my data. For example, I could add a new item, go to the next screen, change something that reloads a previous screen, and SwiftData just forgets the item that I added. Please find the fully working code attached.
While writing this post, I realized that if I use .modelContainer
instead of .modelContext,
the issue is solved. So I have two questions:
-
It seems like
.modelContainer
is the go-to option when working with SwiftData, but why did an issue occur when I used.modelContext
and passed in a shared container? When should we use.modelContext
over.modelContainer?
-
What was the bug? It's working fine in iOS 17, but not in iOS 18. Or is this expected?
Here's the fully working code so you can copy and paste:
import SwiftUI
import SwiftData
typealias NamedColor = (color: Color, name: String)
extension Color {
init(r: Double, g: Double, b: Double) {
self.init(red: r/255, green: g/255, blue: b/255)
}
static let namedColors: [NamedColor] = [
(.blue, "Blue"),
(.red, "Red"),
(.green, "Green"),
(.orange, "Orange"),
(.yellow, "Yellow"),
(.pink, "Pink"),
(.purple, "Purple"),
(.teal, "Teal"),
(.indigo, "Indigo"),
(.brown, "Brown"),
(.cyan, "Cyan"),
(.gray, "Gray")
]
static func name(for color: Color) -> String {
return namedColors.first(where: { $0.color == color })?.name ?? "Blue"
}
static func color(for name: String) -> Color {
return namedColors.first(where: { $0.name == name })?.color ?? .blue
}
}
@main
struct SwiftDataTestApp: App {
var sharedModelContainer: ModelContainer = {
let schema = Schema([
Item.self,
])
let modelConfiguration = ModelConfiguration(schema: schema, isStoredInMemoryOnly: false)
do {
return try ModelContainer(for: schema, configurations: [modelConfiguration])
} catch {
fatalError("Could not create ModelContainer: \(error)")
}
}()
@AppStorage("accentColor") private var accentColorName: String = "Blue"
var body: some Scene {
WindowGroup {
NavigationStack {
HomeView()
}
.tint(Color.color(for: accentColorName))
}
.modelContainer(sharedModelContainer) // This works
// .modelContext(ModelContext(sharedModelContainer)) // This doesn't work
}
}
@Model
final class Item {
var timestamp: Date
init(timestamp: Date) {
self.timestamp = timestamp
}
}
struct HomeView: View {
@State private var showSettings = false
@Environment(\.modelContext) var modelContext
@AppStorage("accentColor") private var accentColorName: String = "Blue"
@Query private var items: [Item]
var body: some View {
List {
ForEach(items) { item in
NavigationLink {
Text("Item at \(item.timestamp, format: Date.FormatStyle(date: .numeric, time: .standard))")
} label: {
Text(item.timestamp, format: Date.FormatStyle(date: .numeric, time: .standard))
}
}
Button {
withAnimation {
let newItem = Item(timestamp: Date())
modelContext.insert(newItem)
}
} label: {
Image(systemName: "plus")
.frame(maxWidth: .infinity)
.frame(maxHeight: .infinity)
}
}
.navigationTitle("Habits")
.toolbar {
ToolbarItem(placement: .navigationBarTrailing) {
Button(action: { showSettings = true }) {
Label("", systemImage: "gearshape.fill")
}
}
}
.navigationDestination(isPresented: $showSettings) {
colorPickerView
}
}
private var colorPickerView: some View {
Form {
Section(header: Text("Accent Color")) {
Picker("Accent Color", selection: $accentColorName) {
ForEach(Color.namedColors, id: \.name) { namedColor in
Text(namedColor.name)
.tag(namedColor.name)
.foregroundColor(namedColor.color)
}
}
.pickerStyle(.wheel)
}
}
.navigationTitle("Settings")
}
}