SwiftUI - memory leak in NavigationView

You don't need to split the close button out in its own view. You can solve this memory leak by adding a capture list to the NavigationView's closure: this will break the reference cycle that retains your viewModel.

You can copy/paste this sample code in a playground to see that it solves the issue (Xcode 11.4.1, iOS playground).

import SwiftUI
import PlaygroundSupport

struct ModalView: View {
    @Environment(\.presentationMode) private var presentation
    @ObservedObject var viewModel: ViewModel

    var body: some View {
        // Capturing only the `presentation` property to avoid retaining `self`, since `self` would also retain `viewModel`.
        // Without this capture list (`->` means `retains`):
        // self -> body -> NavigationView -> Button -> action -> self
        // this is a retain cycle, and since `self` also retains `viewModel`, it's never deallocated.
        NavigationView { [presentation] in
            Text("Modal is presented")
                .navigationBarItems(leading: Button(
                    action: {
                        // Using `presentation` without `self`
                        presentation.wrappedValue.dismiss()
                },
                    label: { Text("close") }))
        }
    }
}

class ViewModel: ObservableObject { // << tested view model
    init() {
        print(">> inited")
    }

    deinit {
        print("[x] destroyed")
    }
}

struct TestNavigationMemoryLeak: View {
    @State private var showModal = false
    var body: some View {
        Button("Show") { self.showModal.toggle() }
            .sheet(isPresented: $showModal) { ModalView(viewModel: ViewModel()) }
    }
}

PlaygroundPage.current.needsIndefiniteExecution = true
PlaygroundPage.current.setLiveView(TestNavigationMemoryLeak())

I was having a gnarly memory leak due to navigationBarItems and passing my view model to the view I was using as the bar item.

Digging around on this, I learned that navigationBarItems is deprecated

I had

        .navigationBarItems(trailing:
            AlbumItemsScreenNavButtons(viewModel: viewModel)
        )

The replacement is toolbar.

My usage now looks like this:

        .toolbar {
            ToolbarItemGroup(placement: .navigationBarTrailing) {
                AlbumItemsScreenNavButtons(viewModel: viewModel)
            }
        }

My solution is

.navigationBarItems(
    trailing: self.filterButton
)

..........................................

var filterButton: some View {
    Button(action: {[weak viewModel] in
        viewModel?.showFilter()
    },label: {
        Image("search-filter-icon").renderingMode(.original)
    })
}

I recommend design-level solution, ie. decomposing navigation bar item into separate view component breaks that undesired cycle referencing that result in leak.

Tested with Xcode 11.4 / iOS 13.4 - ViewModel destroyed as expected.

Here is complete test module code:

struct CloseBarItem: View { // separated bar item with passed binding
    @Binding var presentation: PresentationMode
    var body: some View {
        Button(action: {
            self.presentation.dismiss()
        }) {
            Text("close")
        }
    }
}

struct ModalView: View {
    @Environment(\.presentationMode) private var presentation
    @ObservedObject var viewModel: ViewModel

    var body: some View {

        NavigationView {
            Text("Modal is presented")
            .navigationBarItems(leading: 
                CloseBarItem(presentation: presentation)) // << decompose
        }
    }
}

class ViewModel: ObservableObject {    // << tested view model
    init() {
        print(">> inited")
    }

    deinit {
        print("[x] destroyed")
    }
}

struct TestNavigationMemoryLeak: View {
    @State private var showModal = false
    var body: some View {
        Button("Show") { self.showModal.toggle() }
            .sheet(isPresented: $showModal) { ModalView(viewModel: ViewModel()) }
    }
}

struct TestNavigationMemoryLeak_Previews: PreviewProvider {
    static var previews: some View {
        TestNavigationMemoryLeak()
    }
}