SwiftUI - removing item from list crashes with Fatal error: Index out of range

Question

I have a problem with List in SwiftUI. Removing any item from the list crashes with error Fatal error: Index out of range. It doesn't work using onDelete method and doesn't work in my custom function. What am I doing wrong?

It's macOS app, not iOS. I'm on macOS 10.15.1 and using Xcode 11.2.1.

Here is my code:

import SwiftUI

struct TodoItem: Identifiable {
    var id = UUID()
    var name: String
    var isCompleted = false
}

struct TodoRow: View {
    @Binding var todo: TodoItem
    @State var buttonHover: Bool = false
    var index: Int
    var removeTodo: (_ index: Int) -> Void

    func toggleTodo() {
        self.$todo.isCompleted.wrappedValue.toggle()
    }

    var body: some View {
        VStack(alignment: .leading) {
            HStack {
                Button(action: toggleTodo) {
                    Image(nsImage: NSImage(named: NSImage.Name(NSImage.menuOnStateTemplateName))!)
                        .resizable()
                        .frame(width: 8, height: 8)
                        .padding(3)
                        .opacity(todo.isCompleted ? 1 : buttonHover ? 0.5 : 0)
                }.buttonStyle(PlainButtonStyle())
                    .background(Capsule().stroke(Color.primary, lineWidth: 1))
                    .onHover(perform: { val  in self.buttonHover = val })
                Text("\(todo.name)").strikethrough(todo.isCompleted, color: Color.primary)
            }.opacity(todo.isCompleted ? 0.35 : 1)
            Divider().fixedSize(horizontal: false, vertical: true).frame(height: 1)
        }.contextMenu {
            Button(action: {
                self.removeTodo(self.index)
            }) {
                Text("Remove")
            }
        }
    }
}

struct TodoList: View {
    var listName: String
    @State var newTodo: String = ""
    @State var todos: [TodoItem] = []
    @State var showCompleted = false

    func addTodo() {
        let trimmedTodo = newTodo.trimmingCharacters(in: .whitespacesAndNewlines)
        if !trimmedTodo.isEmpty {
            todos.insert(TodoItem(name: trimmedTodo), at: 0)
            newTodo = ""
        }
    }

    func removeTodo(index: Int) -> Void {
        // remove is crashing the app :(
        self.todos.remove(at: index)
    }

    var body: some View {
        return VStack(alignment: .leading) {
            Text("\(listName)").font(.system(size: 20))
            HStack {
                TextField("New todo...", text: $newTodo)
                NativeButton("Add", keyEquivalent: .return) {
                    self.addTodo()
                }
            }
            List {
                ForEach(todos.indices.filter { self.showCompleted || !self.todos[$0].isCompleted }, id: \.self) { index in
                    TodoRow(todo: self.$todos[index], index: index, removeTodo: self.removeTodo)
                }.onDelete{offsets in
                    // remove is crashing the app :(
                    self.todos.remove(atOffsets: offsets)
                }
            }
            Toggle(isOn: $showCompleted) {
                Text("Show completed")
            }
        }.padding().frame(minWidth: 400, maxWidth: .infinity, minHeight: 200, maxHeight: .infinity)
    }
}

struct TodoList_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

Thanks for your help and sorry for the messy code, I'm still new to Swift and SwiftUI.

Answer 1

So the answer from fakiho (thank you!) was not the complete solution but it helped me find the solution. I think the problem was with @Binding var todo: TodoItem in TodoRow. I ended up passing all properties that I needed instead of whole TodoItem and it's working.

Here is full working code if anyone has the same issue:

struct TodoRow: View {
    @State var buttonHover: Bool = false
    var name: String
    var isCompleted: Bool
    var toggleItem: () -> Void
    var removeItem: () -> Void

    var body: some View {
        VStack(alignment: .leading) {
            HStack {
                Button(action: toggleItem) {
                    Image(nsImage: NSImage(named: NSImage.Name(NSImage.menuOnStateTemplateName))!)
                        .resizable()
                        .frame(width: 8, height: 8)
                        .padding(3)
                        .opacity(isCompleted ? 1 : buttonHover ? 0.5 : 0)
                }.buttonStyle(PlainButtonStyle())
                    .background(Capsule().stroke(Color.primary, lineWidth: 1))
                    .onHover(perform: { val  in self.buttonHover = val })
                Text("\(name)").strikethrough(isCompleted, color: Color.primary)
            }.opacity(isCompleted ? 0.35 : 1)
            Divider().fixedSize(horizontal: false, vertical: true).frame(height: 1)
        }.contextMenu {
            Button(action: removeItem) {
                Text("Delete")
            }
        }
    }
}

struct TodoList: View {
    var listName: String
    @State var newTodo: String = ""
    @State var todos: [TodoItem] = []
    @State var showCompleted = false

    func addTodo() {
        let trimmedTodo = newTodo.trimmingCharacters(in: .whitespacesAndNewlines)
        if !trimmedTodo.isEmpty {
            todos.insert(TodoItem(name: trimmedTodo), at: 0)
            newTodo = ""
        }
    }

    var body: some View {
        return VStack(alignment: .leading) {
            Text("\(listName)").font(.headline)
            HStack {
                TextField("New todo...", text: $newTodo)
                NativeButton("Add", keyEquivalent: .return) {
                    self.addTodo()
                }
            }
            List {
                ForEach(todos.indices.filter { self.showCompleted || !todos[$0].isCompleted }, id: \.self) { index in
                    TodoRow(
                        name: self.todos[index].name,
                        isCompleted: self.todos[index].isCompleted,
                        toggleItem: {
                            self.$todos[index].isCompleted.wrappedValue.toggle()
                        },
                        removeItem: {
                            self.todos.remove(at: index)
                        }
                    )
                }.onDelete { offsets in
                    self.todos.remove(atOffsets: offsets)
                }
            }
            Toggle(isOn: $showCompleted) {
                Text("Show completed")
            }
        }.padding().frame(minWidth: 400, maxWidth: .infinity, minHeight: 200, maxHeight: .infinity)
    }
}

Answer 2

hello I've noticed that you are filtering the indices and I checked the offset on delete and I found out that sometimes the offset range is different that the actual index, I tried to change some things :

      List {
                ForEach(todos.filter { self.showCompleted || !$0.isCompleted }, id: \.self) { item in
                    TodoRow(todo: item)
                }.onDelete{offsets in
                    self.todos.remove(atOffsets: offsets)
                }
            }

and this way need to make TodoItem conform to 'Hashable' -> struct TodoItem: Identifiable, Hashable

so give it a try and hit me back if it didn't solve your problem