swiftui - .sheet : Shows only once and then never again

Question

使用 Beta4 时，似乎该错误仍然存​​在。以下 View 序列(一个列表，点击列表条目打开另一个列表)允许显示 ListView恰好一次； onDisappear永远不会被调用，所以 showModal flag 改变，但不会触发 ListView 的重新显示再次点击时。因此，对于每个 GridCellBodyEntry , .sheet演示文稿只工作一次，然后再也不会。

我尝试了一些建议和解决方法，但都没有奏效(例如，用 NavigationViewModel 封装)。我什至试图删除列表，因为有一个假设是 List导致这种行为，但即使这样也没有改变任何东西。

有什么想法吗？

设置:

一个 GridCellBody此 View :

var body: some View {

        GeometryReader { geometry in

            VStack {

                List {

                    Section(footer: self.footerView) {

                        ForEach(self.rawEntries) { rawEntry in

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

一个 GridCellBodyEntry使用此定义:

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")
        }
    }
}

一个 ListView使用此定义:

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 ?? ""))
        }
    }
}

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 ...
}

哪里 willChange.send()每当发生变化(创建、修改、删除操作)时调用。

Answer 1

这是 swiftUI PresentaionLink does not work second time 的变体

以下简化代码展示了您遇到的行为(该工作表仅显示一次):

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)") })
                }
            }
    }
}

当您输入 .sheet 时，SwiftUI 中似乎存在一个错误。在 List 或 ForEach 中。如果您移动 .sheet在列表之外，您应该能够获得正确的行为。

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)") })
    }
}