SwiftUI app crashes when deleting an object from a list

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Created Jul ’21

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In my app I’ve got a list view and a view for displaying the rows in the list. When I delete an item from that list the app crashes in the row view stating an illegal access.

I don’t understand why the row view is rendered again for the deleted item.

The list view:

import Foundation
import SwiftUI



struct SpanList: View {
  @Environment(\.managedObjectContext) private var viewContext 

  @FetchRequest(
    sortDescriptors: [ NSSortDescriptor(keyPath: \Span.startDate,

                                        ascending: true) ],
    predicate: NSPredicate(format: "isArchived != YES"),
    animation: .default)
  private var activeSpans: FetchedResults<Span>

  var body: some View {
    NavigationView {
      VStack {
        List {
          Section(header: ActiveSectionHeader()) {
            ForEach(activeSpans, id: \.id) { item in
              NavigationLink(destination: getConfiguredEditView(span: item)) {
                SpanRow(span: item)
              }
              .buttonStyle(PlainButtonStyle())
              .listRowBackground(item.color.opacity(0.5))
            }
            .onDelete(perform: deleteItems)
          }
        }
        .listStyle(GroupedListStyle())
      }
    }
  }

  private func getConfiguredEditView(span: Span) -> some View {
    EditSpan(span: span)
      .navigationTitle("Edit Span")
      .navigationBarTitleDisplayMode(.inline)
  }

  private func deleteItems(offsets: IndexSet) {
    withAnimation {
      // Necessary due to a bug in the framework. Without this the app crashes
      // with a bug stating multiple access from different threads is not
      // allowed.
      viewContext.perform {
        offsets.map {
          activeSpans[$0]
        }.forEach(viewContext.delete)
        PersistenceController.shared.save()
      }
    }
  }
}

The row view:

import SwiftUI
import CoreData

struct SpanRow: View {
  @ObservedObject var span: Span

  var body: some View {
    HStack(alignment: .center) {
      VStack(alignment: .leading) {
        HStack {
          if span.showOnStartPage && !span.isArchived {
            Image(systemName: "paperclip")
          }

          Text(span.descriptionString)
            .font(.headline)
            .fontWeight(.bold)
        }

        Spacer()

        HStack {
          // It crashes here 
          Text("\(span.startDate, formatter: dateFormatter)")
          Text("–")

          if span.usesEndDate {
            Text("\(span.endDate, formatter: dateFormatter)")
          } else {
            Image(systemName: "infinity")
          }
        }
      }

      Spacer()

      if let daysSinceStart = span.daysSinceStart {
        VStack {
          Text("\(daysSinceStart)")
            .font(.largeTitle)
            .fontWeight(.semibold)
          Text("days")
        }
      }
    }
    .padding(.vertical, 5)
  }

  private let dateFormatter: DateFormatter = {
    let formatter = DateFormatter()
    formatter.dateStyle = .medium

    return formatter
  }()
}

What am I missing?

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