How to ensure WidgetKit view shows correct results from @FetchRequest?

Question

I have an app that uses Core Data with CloudKit. Changes are synced between devices. The main target has Background Modes capability with checked Remote notifications. Main

Answer 1

Widget views don't observe anything. They're just provided with TimelineEntry data. Which means @FetchRequest, @ObservedObject etc. will not work here.

---

1. Enable remote notifications for your container:

let container = NSPersistentContainer(name: "DataModel")
let description = container.persistentStoreDescriptions.first
description?.setOption(true as NSNumber, forKey: NSPersistentStoreRemoteChangeNotificationPostOptionKey)

2. Update your CoreDataManager to observe remote notifications:

class CoreDataManager {
    var itemCount: Int?

    private var observers = [NSObjectProtocol]()

    init() {
        fetchData()
        observers.append(
            NotificationCenter.default.addObserver(forName: .NSPersistentStoreRemoteChange, object: nil, queue: .main) { _ in
                // make sure you don't call this too often - notifications may be posted in very short time frames
                self.fetchData()
            }
        )
    }

    deinit {
        observers.forEach(NotificationCenter.default.removeObserver)
    }

    func fetchData() {
        let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName: "Item")

        do {
            self.itemCount = try CoreDataStack.shared.managedObjectContext.count(for: fetchRequest)
            WidgetCenter.shared.reloadAllTimelines()
        } catch {
            print("Failed to fetch: \(error)")
        }
    }
}

3. Add another field in the Entry:

struct SimpleEntry: TimelineEntry {
    let date: Date
    let itemCount: Int?
}

4. Use it all in the Provider:

struct Provider: TimelineProvider {
    let coreDataManager = CoreDataManager()

    ...

    func getTimeline(in context: Context, completion: @escaping (Timeline<Entry>) -> Void) {
        let entries = [
            SimpleEntry(date: Date(), itemCount: coreDataManager.itemCount),
        ]

        let timeline = Timeline(entries: entries, policy: .never)
        completion(timeline)
    }
}

5. Now you can display your entry in the view:

struct WidgetExtEntryView: View {
    var entry: Provider.Entry

    var body: some View {
        VStack {
            Text(entry.date, style: .time)
            Text("Count: \(String(describing: entry.itemCount))")
        }
    }
}