SwiftUI ObservedObject not updating across views

Question

I cannot get observable object model to work.

I have a simple demo of two views and a view model. The view model is;

import Foundation

class Score: ObservableObject {

    @Published var total = 0

}

A button view to add one to the total;

struct ScoreButton: View {
    @ObservedObject var score = Score()

    var body: some View {
        Button(action: {
            score.total += 1
        }, label: {
            Text("Add 1 to Total")
        })
    }
}

Then a start view to show the results;

struct OBDemo: View {

    @ObservedObject var result = Score()

    var body: some View {
        VStack {
            ScoreButton()
                .padding()
            Text("Total = \(result.total)")

        }
    }
}

If I put the class, button and start view in one file it works

pawello2222 · Accepted Answer · 2020-09-01 21:25:34Z

0

You're creating the two different instances of Score:

struct ScoreButton: View {
    @ObservedObject var result = Score() // instance #1

struct OBDemo: View {
    @ObservedObject var result = Score() // instance #2

You need to use the same instance in both views - pass the @ObservedObject to the child view:

struct OBDemo: View {
    @ObservedObject var result = Score() // create in the parent view

    var body: some View {
        VStack {
            ScoreButton(result: result) // <- pass to the child view
                .padding()
            Text("Total = \(result.total)")

        }
    }
}

struct ScoreButton: View {
    @ObservedObject var score: Score // declare only

    var body: some View {
        Button(action: {
            score.total += 1
        }, label: {
            Text("Add 1 to Total")
        })
    }
}

answered Sep 1, 2020 at 21:25

pawello2222

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2 Comments

Jmcg Over a year ago

Thank you. How do I update the preview for ScoreButton? static var previews: some View { ScoreButton(score: #?#)

pawello2222 Over a year ago

@Jmcg You can do ScoreButton(score: Score())

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