memory management - How can I initialize View Again in SwiftUI?

Question

I’m using SwfitUI in my project and I have a NavigationView and List. I’m clicking cell after open the detail view and click navigation back button. I want to remove view (it’s struct, in SwiftUI) after click navigation back button. Because if I click the same cell or button again, it isn’t initialize new view, it’s shows old view. I want to do refresh this view. How do I do?

My FirstView Struct is:

struct FirstView: View {

    @ObservedObject var viewModel: FirstViewModel

    var body: some View {
        List(self.viewModel.objects, id: .id) { object in
            ZStack {
                DetailViewCell(object: object)
                NavigationLink(destination: DetailViewBuilder.make(object)) {
                    EmptyView()
                }.buttonStyle(PlainButtonStyle())
            }
        }
    }
}

My DetailView Struct is:

struct DetailView: View {

    @ObservedObject var viewModel: DetailViewModel

    var body: some View {
        ZStack(alignment: .top) {
            Color.mainBackground.edgesIgnoringSafeArea(.all)
            VStack {
                ZStack {
                    Image("Square")
                    Image(self.viewModel.currentImage)
                }
                Text(self.viewModel.currentText)
                    .padding()
                    .frame(alignment: .center)
                    .minimumScaleFactor(0.1)
                Spacer()
                Button(action: {
                    self.viewModel.pressedPlayOrPauseButton()
                }, label: {
                    Image(self.viewModel.isPlaying ? "Pause" : "Play").foregroundColor(Color("Orange"))
                }).padding()
            }
        }
    }
}

First of all, I go to the detail by clicking a cell in FirstView. Then I come back with the back button. I click on a cell again to go to the details, but a new view does not open. It shows the old view.

Before I forget, My Builder Class is:

final class DetailViewBuilder {
    static func make(object: Something) -> DetailView {

        let viewModel = DetailViewModel(object: object)
        let view = DetailView(viewModel: viewModel)

        return view
    }
}

Note: If I will use Sheet Presented, It's working. It's creating new View. But I want to use NavigationLink. Thank you.

Answer 1

You just need to defer your destination creation in your builder, and the @ViewBuilder is a good instrument for this.

It can be used the following wrapper for to create real destination only in when body will be rendered (ie. explicitly in time of navigation clicked in your case)

Tested with Xcode 11.4 / iOS 13.4

struct DeferView<Content: View>: View {
    let content: () -> Content

    init(@ViewBuilder _ content: @escaping () -> Content) {
        self.content = content
    }
    var body: some View {
        content()          // << everything is created here
    }
}

and now your builder

final class DetailViewBuilder {
    static func make(object: Something) -> some View {
        DeferView {
           DetailView(viewModel: DetailViewModel(object: object))
        }
    }
}