SwiftUI Navigationlink或Presentation Link无法正常工作

Question

When using NavigationLink or presentation link in swiftUI, the navigation controller doesn't push or present a new View, getting error

"[WindowServer] display_timer_callback: unexpected state"

ForEach(self.items.identified(by: \.name)) {  item in


    NavigationLink(destination: Text("DT In the House")) {
        CategoryItem(item: item)


    }
}

[] nw_connection_receive_internal_block_invoke [C4] Receive reply failed with error "Operation canceled"

Answer 1

I believe this is bug in PresentationLink in current SwiftUI beta. I get the same error while trying to reopen modal after dismissing it.

EDIT1: NavigationLink requires to be embedded in NavigationView and if there is none will present message [WindowServer] display_timer_callback: unexpected state (now:1abc3d3ccc7 < expected:1abc3d91a0f)

EDIT2: PresentationLink only appears to be buggy while embedded in things like NavigationBarItems or Lists etc.

Answer 2

It seems to be a bug. I've managed to whip up a (dirty) workaround:

private enum SetPresentedViewKey: EnvironmentKey {
    static var defaultValue: (AnyView?) -> () {
        fatalError()
    }
}

private extension EnvironmentValues {
    var setPresentedView: (AnyView?) -> () {
        get {
            self[SetPresentedViewKey.self]
        } set {
            self[SetPresentedViewKey.self] = newValue
        }
    }
}

/// A replacement for the buggy (as of Xcode 11 b3) `PresentationLink`.
public struct PresentationLink2<Destination: View, Label: View>: View {
    public let destination: Destination
    public let label: Label

    @Environment(\.setPresentedView) private var setPresentedView
    @State private var presentedView: AnyView? = nil

    public init(destination: Destination, @ViewBuilder _ label: () -> Label) {
        self.destination = destination
        self.label = label()
    }

    private struct _Body<Destination: View, Label: View>: View {
        @Environment(\.setPresentedView) private var setPresentedView

        let destination: Destination
        let label: Label

        init(destination: Destination, label: Label) {
            self.destination = destination
            self.label = label
        }

        var body: some View {
            Button(action: present, label: { label })
        }

        func present() {
            setPresentedView(AnyView(destination))
        }
    }

    public var body: some View {
        _Body(destination: destination, label: label)
            .environment(\.setPresentedView, { self.presentedView = $0 })
            .presentation(presentedView.map {
                Modal($0, onDismiss: { self.presentedView = nil })
            })
    }
}

Just copy the code above into your codebase and use PresentationLink2 instead of PresentationLink .

---

As noted by @kozlowsqi, PresentationLink seems to be broken when embedded in a NavigationView . What's alarming is that it's still broken as of Xcode beta 3.

Edit: I've filed a radar through the new Feedback Assistant app, FB6525020. Please raise your own and reference mine, and hopefully this will be resolved by beta 4.

Answer 3

I've created a PresentationLink replacement that works far more reliable. Hopefully it won't be needed anymore as soon as beta 4 is released.

You can find a gist here: https://gist.github.com/petercv/3fba967a69b262901053fc8638b7851b

I've also added support for a .isModalInPresentation(_ value: Bool) modifier to set the isModalInPresentation property of UIViewController. Hopefully Apple will add this too soon.