Embedded @Binding does not changing a value

Question

Following this cheat sheet I'm trying to figure out data flow in SwiftUI. So:

Use @Binding when your view needs to mutate a property owned by an ancestor view, or owned by an observable object that an ancestor has a reference to.

And that is exactly what I need so my embedded model is:

class SimpleModel: Identifiable, ObservableObject {
    @Published var values: [String] = []

    init(values: [String] = []) {
        self.values = values
    }
}

and my View has two fields:

struct SimpleModelView: View {
    @Binding var model: SimpleModel
    @Binding var strings: [String]

    var body: some View {
        VStack {
            HStack {
                Text(self.strings[0])
                TextField("name", text: self.$strings[0])
            }
            HStack {
                Text(self.model.values[0])
                EmbeddedView(strings: self.$model.values)
            }
        }
    }
}

struct EmbeddedView: View {
    @Binding var strings: [String]

    var body: some View {
        VStack {
            TextField("name", text: self.$strings[0])
        }
    }
}

So I expect the view to change Text when change in input field will occur. And it's working for [String] but does not work for embedded @Binding object:

Why it's behaving differently?

Asperi · Accepted Answer · 2020-07-24 12:53:33Z

2

Make property published

class SimpleModel: Identifiable, ObservableObject {
    @Published var values: [String] = []

and model observed

struct SimpleModelView: View {
    @ObservedObject var model: SimpleModel

Note: this in that direction - if you introduced ObservableObject then corresponding view should have ObservedObject wrapper to observe changes of that observable object's published properties.

edited Jul 24, 2020 at 12:53

answered Jul 24, 2020 at 12:17

Asperi

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2 Comments

morzelek Over a year ago

Did that - same issue unfortunately

morzelek Over a year ago

Great! Thanks now it's working and understand principle here, but still not sure why @Binding with @Published as you suggested in a first time it's not working 🤔 From my understanding the docs and description it should change Text same way since it's "bind"

Samuel-IH · Accepted Answer · 2020-07-24 12:56:58Z

1

In SimpleModelView, try changing:

@Binding var model: SimpleModel

to:

@ObservedObject var model: SimpleModel

@ObservedObjects provide binding values as well, and are required if you want state changes from classes conforming to ObservableObject

answered Jul 24, 2020 at 12:56

Samuel-IH

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