今日扩展更改后在应用上刷新CoreData

Question

I have an app that is using a today widget. It has shared data by using a group. It is currently displaying data correctly in the widget. If I change the data on the app and then show the widget, it updates correctly. Now, I want to update some of the data on the widget and have it reflect on the app.

The app has a UITableView on it, so I am using NSFetchedResultsController to get the data in the table. The widget scrolls between items in the fetchedResultsController, and displays the data. It's possible to update any number of items while on the widget.

I know that this can be done, because I've seen it done on other apps. I just can't work out how to make the app know when I've updated data on the widget, so that it can be refreshed.

As to what I've tried, not much because I couldn't think of what to try. I did add this:

func controllerDidChangeContent(controller: NSFetchedResultsController) {
    print ("Controller changed")
}

This event fires when I change the data on the app, but does not fire when changing the data from the widget.

Per the suggestion below, I added the following code to viewDidLoad on the app:

    let center = NSNotificationCenter.defaultCenter()

    center.addObserver(self, selector: #selector(self.contextUpdated(_:)),name: NSManagedObjectContextDidSaveNotification,
    object: context)

And then to catch the notification:

@IBAction func contextUpdated(notification: NSNotification) {
    print("Notification recieved")
}

I had the same results as I did with the controllerDidChangeContent event - it fired when making a change to the data on the app, but I got nothing from the widget. My understanding is that the widget and the app are not in the same container, and that's why I'm not receiving the notification.

Another thing I've noticed is that once I've saved data on the widget, the moc on the app no longer lets me save data using it. Perhaps because the context on the widget updated the data and invalidated the context on the app?

Answer 1

NSFetchedResultsController should get updated automatically once you save the moc. However, you can also subscribe to changes when the moc gets saved for specific entities and properties etc. Example code is below to get you started. Once you subscribe to the changes, you can filter out what changed, extract the objects then update your table accordingly.

let center = NotificationCenter.default

center.addObserver(self,
                   selector: #selector(CLASS_NAME_HERE.contextUpdated(_:)),
                   name: NSNotification.Name.NSManagedObjectContextDidSave,
                   object: context)

// we would like to get notified for all changes to the given entity
// if you need more specific data, update the predicate as needed
let entityPredicate = NSPredicate(format: "entity.name == %@", ENTITIY_NAME_HERE)

func contextUpdated(_ notification: Notification) {
    // all changes (inserted, updated, deleted) to the moc matching the predicate are inside notification
    print("\(notification)
}

You can filter the notification as follows. Below is for inserted, but can easily be modified to get updated and deleted objects as well.

let info = (notification as NSNotification).userInfo
if let set = info?[NSInsertedObjectsKey] as? NSSet, let insert = set.allObjects as? [NSManagedObject] {
    let inserted = insert.filter { return predicate.evaluate(with: $0) }
}