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不知道我是否在滥用环境对象的想法，但是在使用发布延迟异步值的环境对象时遇到问题。一个视图导航到下一个视图，但随后“根”被更新，结果导致“回声”，或者即使处理了导航问题。当使用导航之间的转换时，这个问题变得更加明显。是否有正确的使用模式来避免这种情况？或者其他一些解决方案？

任何指导将不胜感激。

附上一个精简的样本来说明问题。

Xcode 12.4 IOS 14.1

final class SetColor: ObservableObject {
    @Published var asyncVal: Bool = false
    
    func flipIt() {
        DispatchQueue.main.asyncAfter(deadline: .now()+0.5, execute: {self.asyncVal.toggle()})
    }
}

struct HomeView: View {
    @StateObject var setCol: SetColor = SetColor()
    @State private var navActive: Bool = false
    var body: some View {
        NavigationView {
            ZStack {
                Color(setCol.asyncVal ? .blue : .purple)
                Button(action: {
                    setCol.flipIt()
                    navActive.toggle()
                }, label: {
                    Text("Change and Move")
                })
                .navigationTitle("Home")
                .toolbar {
                    ToolbarItem(placement: .navigationBarTrailing) {
                        NavigationLink(destination: NavChild1().environmentObject(setCol),isActive: $navActive, label: { Text("GoTo 1 >") })
                    }
                }
            }
        }
    }
}

struct NavChild1: View {
    @EnvironmentObject var setCol: SetColor
    @State private var navActive: Bool = false
    var body: some View {
        ZStack {
            Color(setCol.asyncVal ? .yellow : .orange)
            Button(action: {
                setCol.flipIt()
                navActive.toggle()
            }, label: {
                Text("Change and Move")
            })
            .navigationTitle("Nav 1")
            .toolbar {
                ToolbarItem(placement: .navigationBarTrailing) {
                    NavigationLink(destination: NavChild2().environmentObject(setCol),isActive: $navActive, label: { Text("GoTo 2 >") })
                }
            }
        }
    }
}

struct NavChild2: View {
    @EnvironmentObject var setCol: SetColor
    @State private var navActive: Bool = false
    var body: some View {
        ZStack {
            Color(setCol.asyncVal ? .yellow : .orange)
            Button(action: {
                setCol.flipIt()
                navActive.toggle()
            }, label: {
                Text("Change and Move")
            })
            .navigationTitle("Nav 2")
            .toolbar {
                ToolbarItem(placement: .navigationBarTrailing) {
                    NavigationLink(destination: NavChild3().environmentObject(setCol),isActive: $navActive, label: { Text("GoTo 3 >") })
                }
            }
        }
    }
}

struct NavChild3: View {
    @EnvironmentObject var setCol: SetColor
    @State private var navActive: Bool = false
    var body: some View {
        ZStack {
            Color(setCol.asyncVal ? .yellow : .orange)
            Button(action: {
                setCol.flipIt()
                navActive.toggle()
            }, label: {
                Text("Change and Move")
            })
            .navigationTitle("Nav 3")
            .toolbar {
                ToolbarItem(placement: .navigationBarTrailing) {
                    NavigationLink(destination: NavChild3().environmentObject(setCol), isActive: .constant(false), label: { Text("Go Home") })
                }
            }
        }
    }
}

struct HomeView_Previews: PreviewProvider {
    static var previews: some View {
        HomeView()
    }
}
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1 回答 1

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您不需要在 GCD 操作中设置的最后期限。即使用户没有按下导航，它也会导致导航操作（我已经在项目中测试了代码）。这是因为您在 GCD 队列中累积作业，当它们被执行时，您处于另一个视图中（由于 0.5 的停顿）。顺便说一句，它们会导致导航，因为翻转是观察到的，因此无论谁听，都会执行导航。

无论如何，您要做的就是将调度命令更改为：

DispatchQueue.main.async { self.asyncVal.toggle() }

并且导航将更加顺畅，之后无需执行额外的导航命令。

于 2021-04-27T10:46:11.447 回答