如何将动画添加到由 AnyView 制作的自定义导航项之间的过渡？

Question

有没有办法将动画添加到自定义 NavigationItem 之间的过渡，如 this article 中所述，由 AnyView 制作？

我喜欢这个 NavigationStack 系统的一切，除了无法添加任何动画过渡。

我知道问题与 AnyView 类型擦除 some View 有关，如中所述，并且 Group 似乎更好动画自定义视图导航的选择。

Rather that using AnyView and type-erasure, I prefer to encapsulate the conditional logic inside of a Group view. Then the type you return is Group, which will animate properly.

我运行没有想法，我需要一些帮助。

我会为上下文添加我的代码。

场景代理：

class SceneDelegate: UIResponder, UIWindowSceneDelegate {
...
    let contentView = ContentView().environmentObject(UserData())
...
}

内容视图：

struct ContentView: View {
    @EnvironmentObject var userData: UserData   
    var body: some View {
        NavigationHost()
            .environmentObject(NavigationStack(
                NavigationItem(view: AnyView(
                    (userData.isSignedIn ? AnyView(HomeView()) : AnyView(RegisterView1(profile: Profile.default)) )
                    .transition(.move(edge: .trailing))
                    .animation(Animation.linear(duration: 1))))))
                    //this animation works for some reason, but only this one.
            .environmentObject(UserData())
    }
}

导航主机：

struct NavigationHost: View{
    @EnvironmentObject var navigation: NavigationStack
    @EnvironmentObject var userData: UserData

    var body: some View {
            ZStack {
                    self.navigation.currentView.view
                        .environmentObject(self.userData)
                        .environmentObject(self.navigation)
                    ...
                }
            }
    }
}

导航堆栈：

final class NavigationStack: ObservableObject {
    @Published var viewStack: [NavigationItem] = []
    @Published var currentView: NavigationItem

    init(_ currentView: NavigationItem ){
        print("Navigation Stack Initialized")
        self.currentView = currentView
    }

    func back() {
        if viewStack.count == 0 {
            return
        }
        let last = viewStack.count - 1
        currentView = viewStack[last]
        viewStack.remove(at: last)
    }

    navigation.advance(NavigationItem(AnyView))
    func advance(_ view: NavigationItem) {
        viewStack.append( currentView )
        currentView = view
    }

    func home() {
       currentView = NavigationItem( view: AnyView(HomeView()) )
       viewStack.removeAll()
    }

}

struct NavigationItem{
    var view: AnyView
}

Answer 1

此处更新了该文章中的实体，以在屏幕之间采用简单的动画转换。所有这些都是粗糙的，仅用于演示，但希望它能以某种方式提供帮助。

注意：过渡在预览版中不起作用（至少在我的 Xcode 11.2/iOS 13.2 中），因此在模拟器或真实设备中进行了测试。

外观如下：

代码如下：

final class NavigationStack: ObservableObject {
    enum Direction {
        case root
        case forward
        case backward
    }

    @Published var viewStack: [NavigationItem] = []
    @Published var currentView: NavigationItem
    @Published var navigate: Direction = .root

    init(_ currentView: NavigationItem ){
        self.currentView = currentView
    }
    func unwind(){
        if viewStack.count == 0{
            return
        }
        let last = viewStack.count - 1
        currentView = viewStack[last]
        withAnimation {
            self.navigate = .backward
        }
        viewStack.remove(at: last)
    }
    func advance(_ view:NavigationItem){
        viewStack.append( currentView)
        currentView = view
        withAnimation {
            self.navigate = .forward
        }
    }
    func home( ){
        currentView = NavigationItem(view: AnyView(HomeView()))
        viewStack.removeAll()
        withAnimation {
            self.navigate = .root
        }
    }
}

struct NavigationHost: View{
    @EnvironmentObject var navigation: NavigationStack

    var body: some View {
        ZStack(alignment: .topLeading) {
            if navigation.navigate == .root {
                self.navigation.currentView.view
            }
            else if navigation.navigate == .backward {
                self.navigation.currentView.view
                    .transition(.move(edge: .leading))
            }
            if navigation.navigate == .forward {
                self.navigation.currentView.view
                    .transition(.move(edge: .trailing))
            }
        }

    }
}

如何将动画添加到由 AnyView 制作的自定义导航项之间的过渡？

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