Change on ObservableObject in @Published array does not update the view

Question

I've been struggling for hours on an issue with SwiftUI.

Here is a simplified example of my issue :

class Parent: ObservableObject {
    @Published var children = [Child()]
}

class Child: ObservableObject {
    @Published var name: String?

    func loadName() {
        DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
            // Async task here...
            self.objectWillChange.send()
            self.name = "Loaded name"
        }
    }

}

struct ContentView: View {
    @ObservedObject var parent = Parent()

    var body: some View {
        Text(parent.children.first?.name ?? "null")
            .onTapGesture {
                self.parent.objectWillChange.send()
                self.parent.children.first?.loadName() // does not update
            }
    }
}

I have an ObservableObject (Parent) storing a @Published array of ObservableObjects (Child).

The issue is that when the name property is changed via an async task on one object in the array, the view is not updated.

Do you have any idea ?

Many thanks Nicolas

Check out this question here: https://stackoverflow.com/q/58406287/4938203 — Daniel Amarante, Apr 17 '20 at 21:01
Does this answer your question? [How to tell SwiftUI views to bind to nested ObservableObjects](https://stackoverflow.com/questions/58406287/how-to-tell-swiftui-views-to-bind-to-nested-observableobjects) — NikzJon, Apr 18 '20 at 12:03

score 2 · Answer 1 · answered Apr 18 '20 at 04:35

I would say it is design issue. Please find below preferable approach that uses just pure SwiftUI feature and does not require any workarounds. The key idea is decomposition and explicit dependency injection for "view-view model".

Tested with Xcode 11.4 / iOS 13.4

class Parent: ObservableObject {
    @Published var children = [Child()]
}

class Child: ObservableObject {
    @Published var name: String?

    func loadName() {
        DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
            // Async task here...
            self.name = "Loaded name"
        }
    }
}

struct FirstChildView: View {
    @ObservedObject var child: Child
    var body: some View {
        Text(child.name ?? "null")
            .onTapGesture {
                self.child.loadName()
            }
    }
}

struct ParentContentView: View {
    @ObservedObject var parent = Parent()

    var body: some View {
        // just for demo, in real might be conditional or other UI design
        // when no child is yet available
        FirstChildView(child: parent.children.first ?? Child())
    }
}

score 2 · Answer 2 · answered Apr 18 '20 at 05:09

2

Make sure your Child model is a struct! Classes doesn't update the UI properly.

answered Apr 18 '20 at 05:09

SwiftiSwift

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2

One thing to note, it appears that in SwiftUI 2.0 @Published is only available for properties of classes. – charlemagne_vi Nov 04 '20 at 16:37

score -1 · Answer 3 · answered Apr 18 '20 at 01:11

this alternative approach works for me:

class Parent: ObservableObject {
@Published var children = [Child()]
}

class Child: ObservableObject {
@Published var name: String?

func loadName(handler: @escaping () -> Void) {
    DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
        // Async task here...
        self.name = UUID().uuidString  // just for testing
        handler()
    }
}
}

struct ContentView8: View {
@ObservedObject var parent = Parent()
var body: some View {
    Text(parent.children.first?.name ?? "null").padding(10).border(Color.black)
        .onTapGesture {
            self.parent.children.first?.loadName(){
                self.parent.objectWillChange.send()
            }
    }
}
}

Change on ObservableObject in @Published array does not update the view

3 Answers3