如何在从 AnyView 制作的自定义 NavigationItem 之间向 Transitons 添加动画？

Question

有没有办法为自定义之间NavigationItem的过渡添加动画，AnyView如本文所述？

我喜欢这个NavigationStack系统的一切，除了不能添加任何动画过渡。

我理解这个问题有型擦除做some Views的AnyView，如在这个答案，这Group似乎是动画自定义视图导航一个更好的选择。

与其使用 AnyView 和类型擦除，我更喜欢将条件逻辑封装在 Group 视图中。然后您返回的类型是 Group，它将正确地设置动画。

我已经没有想法了，我需要一些帮助。

我将添加我的上下文代码。

场景委托：

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

这是该文章中更新的实体，以在屏幕之间采用简单的动画过渡。所有这些都是沙哑的，仅用于演示，但希望它可以以某种方式有所帮助。

注意：过渡在预览中不起作用（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。

这是它的外观：

这是代码：

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))
            }
        }

    }
}