View.onReceive doesn't cancel subscription when the view removed from hierarchy

user_1434829 0
Viewed 286

It seems View.onReceive doesn't cancel subscription after that view disappeared. Action keeps getting called when no Child view on screen. How can I keep that subscription alive while the view is visible only?

struct BugDemo: View {
    var body: some View {
        NavigationView {
            NavigationLink("Go to child", destination: Child())
        }
    }
}

struct Child: View {
    @State private var date: Date = Date()

    var body: some View {
        Text(DateFormatter.localizedString(from: date, dateStyle: .medium, timeStyle: .medium))
            .navigationBarTitle("Child")
            .onReceive(PublisherHolder.shared.publisher) {
                print("Child.onReceive")
                self.date = $0
            }
            .onDisappear {
                print("Child.onDisappear")
            }
    }
}

private class PublisherHolder {
    static let shared = PublisherHolder()
    lazy var publisher: AnyPublisher<Date, Never> = {
        Timer.publish(every: 1, on: .main, in: .default)
            .autoconnect()
            .print()
            .eraseToAnyPublisher()
    }()
}
combine swiftui
1 Answers

This is not .onReceive. This is NavigationView behaviour. Fortunately or not, it caches navigation stack for possible reuse.

If you instead use the following show/hide for Child you'll see that everything cancelled correctly.

Tested with Xcode 11.4

    @State private var showChild = false
    var body: some View {

        VStack {
            Button("Toggle View") { self.showChild.toggle() }
            if showChild {
                Child()
            }
        }
//            NavigationView {
//                NavigationLink("Go to child", destination: Child())
//            }
    }
user_122990300
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