.sheet:只显示一次，以后再也不显示 [英] .sheet: Shows only once and then never again

问题描述

使用 Beta4 时，似乎该错误仍然存​​在.下面的视图序列(一个列表，点击一个列表条目会打开另一个列表)允许只显示一次 ListView；onDisappear 永远不会被调用，因此 showModal 标志会发生变化，但再次点击时不会触发 ListView 的重新显示.因此，对于每个 GridCellBodyEntry，.sheet 演示文稿只工作一次，以后再也不会工作了.

Working with Beta4, it seems that the bug is still existing. The following sequence of views (a list, where a tap on a list entry opens another list) allows to present the ListView exactly once; the onDisappear is never called, so the showModal flag changes, but does not triggers the redisplay of ListView when tapped again. So, for each GridCellBodyEntry, the .sheet presentation works exactly once, and then never again.

我尝试了一些建议和解决方法，但都没有奏效(例如，使用 NavigationViewModel 进行封装).我什至试图删除 List，因为假设 List 会导致这种行为，但即使这样也没有改变任何东西.

I tried around with several suggestions and workarounds, but none worked (e.g., encapsulating with a NavigationViewModel). I even tried to remove the List, because there was an assumption that the List causes that behaviour, but even this did not change anything.

有什么想法吗?

设置:

1. 带有此视图的 GridCellBody:

var body: some View {

        GeometryReader { geometry in

            VStack {

                List {

                    Section(footer: self.footerView) {

                        ForEach(self.rawEntries) { rawEntry in

                            GridCellBodyEntry(entityType: rawEntry)
                        }
                    }
                }
                .background(Color.white)
            }
        }
    }

1. 具有以下定义的 GridCellBodyEntry:

struct GridCellBodyEntry: View {


    let entityType: EntityType
    let viewModel: BaseViewModel


    init(entityType: EntityType) {

        self.entityType = entityType
        self.viewModel = BaseViewModel(entityType: self.entityType)
    }


    @State var showModal = false {

        didSet {

            print("showModal: \(showModal)")
        }
    }


    var body: some View {

        Group {

            Button(action: {

                self.showModal.toggle()
            },
                   label: {

                    Text(entityType.localizedPlural ?? "")
                        .foregroundColor(Color.black)
            })
            .sheet(isPresented: $showModal, content: {

                ListView(showModal: self.$showModal,
                         viewModel: self.viewModel)
            })
        }.onAppear{
            print("Profile appeared")
        }.onDisappear{
            print("Profile disappeared")
        }
    }
}

1. 具有以下定义的 ListView:

struct ListView: View {


    // MARK: - Private properties


    // MARK: - Public interface


    @Binding var showModal: Bool
    @ObjectBinding var viewModel: BaseViewModel


    // MARK: - Main view


    var body: some View {

        NavigationView {

            VStack {

                List {

                    Section(footer: Text("\(viewModel.list.count) entries")) {

                        ForEach(viewModel.list, id: \.objectID) { item in

                            NavigationLink(destination: ItemView(),
                                           label: {

                                            Text("\(item.objectID)")
                            })
                        }
                    }
                }
            }
            .navigationBarItems(leading:

                Button(action: {

                    self.showModal = false
                }, label: {

                    Text("Close")
                }))

            .navigationBarTitle(Text(viewModel.entityType.localizedPlural ?? ""))
        }
    }
}

1. BaseViewModel(摘录):

class BaseViewModel: BindableObject {

    /// The binding support. 
    var willChange = PassthroughSubject<Void, Never>()

    /// The context.
    var context: NSManagedObjectContext

    /// The current list of typed items.
    var list: [NSManagedObject] = []

    // ... other stuff ...
}

其中 willChange.send() 每当发生变化(创建、修改、删除操作)时都会调用.

where willChange.send() is called whenever something changes (create, modify, delete operations).

推荐答案

这是 swiftUI PresentaionLink 第二次不工作

以下简化代码展示了您遇到的行为(工作表仅显示一次):

The following simplified code exhibits the behavior you're experiencing (the sheet only displays once):

import SwiftUI

struct ContentView: View {
    @State var isPresented = false
    @State var whichPresented = -1

    var body: some View {
        NavigationView {
            List {
                ForEach(0 ..< 10) { i in
                    Button(action: {
                            self.whichPresented = i
                            self.isPresented.toggle()
                        })
                        { Text("Button \(i)") }
                    }.sheet(isPresented: $isPresented, content: { 
Text("Destination View \(self.whichPresented)") })
                }
            }
    }
}

当您将 .sheet 放入 List 或 ForEach 时，SwiftUI 中似乎存在错误.如果您将 .sheet 移到列表之外，您应该能够获得正确的行为.

There appears to be a bug in SwiftUI when you put the .sheet inside a List or a ForEach. If you move the .sheet outside of the List, you should be able to get the correct behavior.

import SwiftUI

struct ContentView: View {
    @State var isPresented = false
    @State var whichPresented = -1

    var body: some View {
        NavigationView {
            List {
                ForEach(0 ..< 10) { i in
                    Button(action: {
                            self.whichPresented = i
                            self.isPresented.toggle()
                        })
                        { Text("Button \(i)") }
                    }
                }
            }.sheet(isPresented: $isPresented, content: { Text("Destination View \(self.whichPresented)") })
    }
}

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