shufflingb / swiftui-core-data-with-model Goto Github PK

The init of the app occurs as follows

    init() {
        _model = StateObject(wrappedValue: AppModel())
    }

When I set as model, the compiler complains with Cannot assign to property: 'model' is a get-only property

For which reason does adding an underscore in front of the var fix this particular case issue? What are we telling the compiler?

It's by searching the solution on google that I stumbled on this post but I don't understand the implications, nor why it isn't possible in other (more verbose) code.

You can inject @StateObject during initialization by unwrapping the property with _

Is this in the official Apple documentation? How did you find this solution?

This project was super helpful. I didn't understand much of what I read about Combine with Core Data until I looked through your code. Thank you!

I have a question for you. Let's pretend you have another Entity in Core Data called Project. A user can select various projects and view Items within each (one Project, many Items). When they switch the project in the UI, it should update which project is referenced in an NSPredicate here:

extension Item {
    // MARK: - NSFetchRequests for Items
    @nonobjc public class func fetchItemsAll() -> NSFetchRequest<Item> {
        let name = "\(Self.self)"
        print("Running fetch request \(name) for all")
        let request = NSFetchRequest<Item>(entityName: name)
        request.sortDescriptors = []
        request.predicate = NSPredicate(format: "project = %@", project) //<-- predicate here
        return request
    }
}

It seems that once the publishers are set up, they are only set to use whatever is initially defined for project. But if the user changes it, I need the publisher to execute again, perform a new fetch request, and deliver the updated data to my views.

Any idea how I might pull that off? I assume that project would live in its own ObservableObject like this:

class AppState: ObservableObject{
  static let shared = AppState()
  @Published var project: Project!
}

...but I don't understand how to make the publishers fire again based on the project change.

Any ideas?