SwiftUI - 将 @Binding 与核心数据 NSManagedObject 一起使用? [英] SwiftUI - Use @Binding with Core Data NSManagedObject?

问题描述

我正在尝试制作一个编辑表单，该表单可以将值作为 @Binding 进行编辑，然后提交更改.在这种情况下，我使用 @FetchRequest 属性包装器填充包含核心数据记录的列表.我想点击一行从列表导航到详细信息视图，然后在详细信息视图上导航到编辑视图.

I'm trying to make an edit form that can take a value as a @Binding, edit it, and commit the change. In this case, I'm populating a list with Core Data records using the @FetchRequest property wrapper. I want to tap on a row to navigate from the List to a Detail view, then on the Detail view I want to navigate to the Edit view.

我尝试在没有 @Binding 的情况下执行此操作，代码将编译，但是当我进行编辑时，它不会反映在之前的屏幕上.似乎我需要使用@Binding，但我无法找到一种方法来在 List 或 ForEach 中获取 NSManagedObject 实例，并将其传递给可以将其用作 @Binding 的视图.

I tried doing this without the @Binding and the code will compile but when I make an edit, it is not reflected on the previous screens. It seems like I need to use @Binding but I can't figure out a way to get a NSManagedObject instance inside of a List or ForEach, and pass it to a view that can use it as a @Binding.

struct TimelineListView: View {

    @Environment(\.managedObjectContext) var managedObjectContext

    // The Timeline class has an `allTimelinesFetchRequest` function that can be used here
    @FetchRequest(fetchRequest: Timeline.allTimelinesFetchRequest()) var timelines: FetchedResults<Timeline>

    @State var openAddModalSheet = false

    var body: some View {

        return NavigationView {
            VStack {
                List {

                    Section(header:
                        Text("Lists")
                    ) {
                        ForEach(self.timelines) { timeline in

                            // ✳️ How to I use the timeline in this list as a @Binding?

                            NavigationLink(destination: TimelineDetailView(timeline: $timeline)) {
                                TimelineCell(timeline: timeline)
                            }
                        }
                    }
                    .font(.headline)

                }
                .listStyle(GroupedListStyle())

            }

            .navigationBarTitle(Text("Lists"), displayMode: .inline)

        }

    } // End Body
}

详细视图

struct TimelineDetailView: View {

    @Environment(\.managedObjectContext) var managedObjectContext

    @Binding var timeline: Timeline

    var body: some View {

        List {

            Section {

                NavigationLink(destination: TimelineEditView(timeline: $timeline)) {
                    TimelineCell(timeline: timeline)
                }

            }

            Section {

                Text("Event data here")
                Text("Another event here")
                Text("A third event here")

            }


        }.listStyle(GroupedListStyle())

    }
}

编辑视图

struct TimelineEditView: View {

    @Environment(\.managedObjectContext) var managedObjectContext

    @Environment(\.presentationMode) var presentationMode: Binding<PresentationMode>

    @State private var newDataValue = ""

    @Binding var timeline: Timeline

    var body: some View {

        return VStack {

            TextField("Data to edit", text: self.$newDataValue)
                .shadow(color: .secondary, radius: 1, x: 0, y: 0)
                .textFieldStyle(RoundedBorderTextFieldStyle())
                .onAppear {
                    self.newDataValue = self.timeline.name ?? ""
            }.padding()
            Spacer()
        }

            .navigationBarItems(
                leading:
                Button(action: ({
                    // Dismiss the modal sheet
                    self.newDataValue = ""
                    self.presentationMode.wrappedValue.dismiss()

                })) {
                    Text("Cancel")
                },

                trailing: Button(action: ({

                    self.timeline.name = self.newDataValue


                    do {
                        try self.managedObjectContext.save()
                    } catch {
                        print(error)
                    }

                    // Dismiss the modal sheet
                    self.newDataValue = ""
                    self.presentationMode.wrappedValue.dismiss()

                })) {
                    Text("Done")
                }
        )

    }
}

我应该提到，我什至尝试这样做的唯一原因是因为模态 .sheet() 东西是超级错误的.

I should mention, the only reason I'm even trying to do this is because the modal .sheet() stuff is super buggy.

推荐答案

@Binding 仅适用于结构体.

但 CoreData 结果是对象(NSManagedObject 采用 ObservableObject).您需要使用 @ObservedObject 来注册更改.

But CoreData result are Objects (NSManagedObject adopting ObservableObject). You need to use @ObservedObject to register for changes.

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