如何删除SwiftUI中的详细信息视图(编辑项视图)中的核心数据条目？

我在SwiftUI中做了一个非常简单的应用程序。使用核心数据的TODO列表。我可以添加做项目，并存储他们的核心数据。项显示在内容视图中的列表中。点击每个项目，我们就会看到EditItemView。我设法为每个条目显示了正确的数据。从这个视图中，我想删除我在EditItemView中看到的这个特定条目。它的工作方式应该类似于在iOS上删除提醒应用程序中的列表。DELETE按钮应该删除这个特定的条目，然后带我们回到ContentView。但是.。什么都没发生。我没有收到任何错误，但什么也没有删除。

核心数据在核心数据中，我有一个实体：ToDoItem(Module：Current ProductModule，Codegen：class Definition)属性：createdAt：Date(今天的默认值)标题：string(默认值=空字符串)

下面是我到目前为止掌握的代码：

内容视图

import SwiftUI

struct ContentView: View {

    @Environment(\.managedObjectContext) var managedObjectContext
    @FetchRequest(
        entity: ToDoItem.entity(),
        sortDescriptors: [
            NSSortDescriptor(keyPath: \ToDoItem.createdAt, ascending: true),
            NSSortDescriptor(keyPath: \ToDoItem.title, ascending: true)
        ]
    ) var toDoItems: FetchedResults<ToDoItem>

    @State private var show_modal: Bool = false

    var body: some View {
        NavigationView {
            List{
                ForEach(toDoItems, id: \.self) {todoItem in

                    NavigationLink(destination: EditItemView(createdAt: todoItem.createdAt!, title: todoItem.title!)) {

                        ToDoItemView(title: todoItem.title!, createdAt: todoItem.createdAt!)
                    }
                }

            }
            .navigationBarTitle(Text("My List"))
            .navigationBarItems(trailing:
                Button(action: {
                    self.show_modal = true
                }) {
                    Text("Add")
                }.sheet(isPresented: self.$show_modal) {
                    AddItemView().environment(\.managedObjectContext, self.managedObjectContext)
                }
            )
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
        return ContentView().environment(\.managedObjectContext, context)
    }
}

编辑视图

import SwiftUI

struct AddItemView: View {

    @Environment(\.presentationMode) var presentationMode
    @Environment(\.managedObjectContext) var managedObjectContext

    static let dateFormat: DateFormatter = {
        let formatter = DateFormatter()
        formatter.dateStyle = .medium
        return formatter
    }()

    @State private var createdAt : Date = Date()
    @State private var showDatePicker = false
    @State private var title = ""

    var body: some View {
        NavigationView {
            ScrollView {

                HStack {
                    Button(action: {
                        self.showDatePicker.toggle()
                    }) {
                        Text("\(createdAt, formatter: Self.dateFormat)")
                    }

                    Spacer()
                }

                if self.showDatePicker {
                    DatePicker(
                        selection: $createdAt,
                        displayedComponents: .date,
                        label: { Text("Date") }
                    )
                        .labelsHidden()
                }


                TextField("to do item", text: $title)
                    .font(Font.system(size: 30))

                Spacer()

            }
            .padding()
            .navigationBarTitle(Text("Add transaction"))

            .navigationBarItems(
                leading:
                Button(action: {
                    self.presentationMode.wrappedValue.dismiss()
                }) {
                    Text("Cancel")
                },

                trailing:
                Button(action: {
                    let toDoItem = ToDoItem(context: self.managedObjectContext)
                    toDoItem.createdAt = self.createdAt
                    toDoItem.title = self.title

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

                    self.presentationMode.wrappedValue.dismiss()
                }) {
                    Text("Done")
                }
            )

        }
    }
}

struct AddItemView_Previews: PreviewProvider {
    static var previews: some View {
        AddItemView()
    }
}

EditItemView

import SwiftUI

struct EditItemView: View {

@Environment(\.managedObjectContext) var managedObjectContext

static let dateFormat: DateFormatter = {
    let formatter = DateFormatter()
    formatter.dateStyle = .medium
    return formatter
}()

var createdAt : Date
var title: String = ""

@State private var newCreatedAt : Date = Date()
@State private var showDatePicker = false
@State private var newTitle = ""

var body: some View {
    ScrollView {

        HStack {
            Button(action: {
                self.showDatePicker.toggle()
            }) {
                Text("\(createdAt, formatter: Self.dateFormat)")
            }

            Spacer()
        }

        if self.showDatePicker {
            DatePicker(
                selection: $newCreatedAt,
                displayedComponents: .date,
                label: { Text("Date") }
            )
                .labelsHidden()
        }


        TextField(title, text: $newTitle)
            .font(Font.system(size: 30))

    }
    .padding()
    .navigationBarTitle(Text("Edit transaction"))
    .navigationBarItems(
        trailing:
        Button(action: {
            print("Delete")

            let deleteToDoItem = ToDoItem(context: self.managedObjectContext)
            self.managedObjectContext.delete(deleteToDoItem)

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

// let deleteToDoItem = self.toDoItems[indexSet.first!] // self.managedObjectContext.delete(deleteToDoItem) // // do { // try self.managedObjectContext.save() // }catch{ // print(error) // }

        }) {
            Text("Delete")
                .foregroundColor(.red)
        }
    )
}

}

struct EditItemView_Previews: PreviewProvider { static var previews: some View { EditItemView( createdAt: Date(), title: "to do item" ) } } 托依坦视图

import SwiftUI

struct ToDoItemView: View {

    static let dateFormat: DateFormatter = {
        let formatter = DateFormatter()
        formatter.dateStyle = .medium
        return formatter
    }()

    var title:String = ""
    var createdAt:Date = Date()

    var body: some View {
        HStack{
            VStack(alignment: .leading){
                Text(title)
                    .font(.headline)
                Text("\(createdAt, formatter: Self.dateFormat)")
                    .font(.caption)
            }
        }
    }
}

struct ToDoItemView_Previews: PreviewProvider {
    static var previews: some View {
        ToDoItemView(title: "To do item", createdAt: Date())
    }
}

P.S.我知道我可以在列表视图中添加.onDelete。但我想故意让用户更难删除一个项目。这就是为什么我想将“删除”按钮移动到“详细信息”视图。