How can I create a two-way binding with a value stored using Core Data?

Question

I am getting the following error when I try to bind to a nested property of an observed object from Core Data: Cannot convert value of type 'Binding<String?>' to expected argument type 'Binding<String>'

Below is a simplified overview:

Parent.swift

@FetchRequest(
    sortDescriptors: [NSSortDescriptor(keyPath: \Item.timestamp, ascending: true)],
    animation: .default)
private var items: FetchedResults<Item>

var body: some View {
    NavigationView {
        List {
            ForEach(items) { item in
                Cell(showing: item)
            }
// ...

Cell.swift

struct Cell: View {
    @ObservedObject var item: Item
    
    init(showing: Item) {
        self.item = showing
    }

    var body: some View {
        TextField("Name", text: $item.name) // <-- error shows for this line
// ...

Why does this show an error? How can I create a two-way binding on this textfield with a value stored using Core Data?

Does this answer your question? [SwiftUI Optional TextField](https://stackoverflow.com/questions/57021722/swiftui-optional-textfield) — lorem ipsum, Jul 01 '21 at 22:10
@loremipsum I looked at that question but the top answer did not solve my problem — Streetlamp, Jul 01 '21 at 22:11
The one with bound? That is hands down the best solution for this. It is the cleanest. You can reuse it too. In your code you will use it $item.name.bound and it will work just copy and paste the code anywhere — lorem ipsum, Jul 01 '21 at 22:13
Shoot, I admit I didn't look past the most upvoted one (by Johnathan), I just tried it and it did end up working actually (good news because it works, but bad because the time expended on the question)! — Streetlamp, Jul 01 '21 at 22:21
Don’t be distracted by the most upvoted. Sometimes the lonely comment has the clue you need. — lorem ipsum, Jul 01 '21 at 22:24

score 0 · Accepted Answer · answered Jul 01 '21 at 22:02

0

It is there, in the error - TextField requires String binding, and item.name is String? (optional) binding. You can bypass it by making custom binding. Something like this:

TextField("", text: Binding(get: { item.name }, set: { newValue in item.name = newValue }))

answered Jul 01 '21 at 22:02

Predrag Samardzic

2,661
15
18

Thank you, that worked. I noticed that this does not commit changes back to Core Data, would I need to complete the set portion of the binding to write the changes back or is there a more idiomatic way to do that? – Streetlamp Jul 01 '21 at 22:08
1

You probably need to save the changes to Core Data, calling managedObjectContext.save() when needed. I would suggest doing the saving on some action, like button press, or textField's onCommit/onSubmit (https://developer.apple.com/documentation/swiftui/textfield/init(_:text:oneditingchanged:oncommit:)-588cl), instead of saving it on every "set". – Predrag Samardzic Jul 01 '21 at 22:13

How can I create a two-way binding with a value stored using Core Data?

1 Answers1