@Published property not updating view from nested view model - SwiftUI

Question

I'm unsure why my view isn't getting updated when I have a view model nested inside another. My understanding was that a @Published property in the child view model would trigger a change in the parent viewModel, causing that to push changes to the UI.

This is the child view model:

class FilterViewModel : ObservableObject, Identifiable {

    var id = UUID().uuidString
    var name  = ""
    var backgroundColour = ""
    @Published var selected = false

    private var cancellables = Set<AnyCancellable>()

    init(name: String){
        self.name = name
    
        $selected.map { _ in
            self.selected ? "Orange" : "LightGray"
        }
        .assign(to: \.backgroundColour, on: self)
        .store(in: &cancellables)
     }

    func changeSelected() {
    
        self.selected = !self.selected
    }
}

The following works as expected, on clicking the button the background colour is changed.

struct ContentView: View {

    @ObservedObject var filterVM = FilterViewModel(name: "A")


    Button(action: { filterVM.changeSelected()}, label: {
        Text(filterVM.name)
            .background(Color(filterVM.backgroundColour))
    })
}

However, I want to have an array of filter view models so tried:

class FilterListViewModel: ObservableObject {

    @Published var filtersVMS = [FilterViewModel]()

    init(){
        filtersVMS = [
            FilterViewModel(name: "A"),
            FilterViewModel(name: "B"),
            FilterViewModel(name: "C"),
            FilterViewModel(name: "D")
        ]
    }
}

However, the following view is not updated when clicking the button

struct ContentView: View {

    @ObservedObject var filterListVM = FilterListViewModel()

    Button(action: { filterListVM[0].changeSelected()}, label: {
        Text(filterListVM[0].name)
            .background(Color(filterListVM[0].backgroundColour))
    })
}

Asperi · Accepted Answer · 2020-12-13 05:13:04Z

5

Alternate solution is to use separated view for your sub-model:

struct FilterView: View {
    @ObservedObject var filterVM: FilterViewModel

    var body: some View {
      Button(action: { filterVM.changeSelected()}, label: {
        Text(filterVM.name)
            .background(Color(filterVM.backgroundColour))
      })
    }
}

so in parent view now we can just use it as

struct ContentView: View {

    @ObservedObject var filterListVM = FilterListViewModel()

    // ...

    FilterView(filterVM: filterListVM[0])
}

answered Dec 13, 2020 at 5:13

Asperi

262k28 gold badges594 silver badges888 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Spdollaz Over a year ago

Thanks, this worked perfectly. Do you know why this works rather than referencing the child VM through its parent?

Asperi Over a year ago

ObservedObject observes only one level published values changing, in your case reference to child is not changed when internal child properties changed.

davidev · Accepted Answer · 2020-12-12 22:09:18Z

0

The most simplest way is to define your FilterViewModel as struct. Hence, it is a value type. When a value changes, the struct changes. Then your ListViewModel triggers a change.

struct FilterViewModel : Identifiable {

    var id = UUID().uuidString
    var name  = ""
    var backgroundColour = ""
    var selected = false

    private var cancellables = Set<AnyCancellable>()

    init(name: String){
        self.name = name
    
        $selected.map { _ in
            self.selected ? "Orange" : "LightGray"
        }
        .assign(to: \.backgroundColour, on: self)
        .store(in: &cancellables)
     }

    mutating func changeSelected() {
    
        self.selected = !self.selected
    }
}

answered Dec 12, 2020 at 22:09

davidev

8,6955 gold badges35 silver badges70 bronze badges

Collectives™ on Stack Overflow

@Published property not updating view from nested view model - SwiftUI

2 Answers 2

2 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related