c# - 无法删除该对象，因为在 ObjectStateManager #2 中找不到它

Question

我在屏幕截图中发现了问题:

这是程序开头的代码:

    public MainWindow()
    {
        InitializeComponent();


        BlackoutDates();

        variables.date = Convert.ToDateTime(MainCalendar.DisplayDate);
        DateOutput.Content = MainCalendar.DisplayDate.DayOfWeek + ", " + MainCalendar.DisplayDate.ToShortDateString();



    }

    //initialises entities
    WpfApplication7.AllensCroftEntities1 allensCroftEntities1 = new WpfApplication7.AllensCroftEntities1();
    private Booking ObjectIndex;

这是加载窗口时的代码

 private void Bookings_Loaded(object sender, RoutedEventArgs e)
    {


       WpfApplication7.AllensCroftEntities1 allensCroftEntities1 = new WpfApplication7.AllensCroftEntities1();
        // Load data into Rooms.
        var roomsViewSource = ((CollectionViewSource)(this.FindResource("roomsViewSource")));
        var roomsQuery = this.GetRoomsQuery(allensCroftEntities1);
        roomsViewSource.Source = roomsQuery.Execute(MergeOption.AppendOnly);

    }

这是导致错误的删除按钮的代码:

 private void btnDelete_Click(object sender, RoutedEventArgs e)
    {

        //prevents user trying to delete nothing/unselected row
        if (ObjectIndex == null)
        {
            MessageBox.Show("Cannot delete the blank entry");
        }
        else
        {

            //deletes object from dataset, saves it and outputs a message
            allensCroftEntities1.DeleteObject(ObjectIndex);

            allensCroftEntities1.SaveChanges();
            MessageBox.Show("Booking Deleted");
        }
    }

这是对象索引的代码:

   private void listrow_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {

        //outputs index of the selected room
        ObjectIndex = listrow.SelectedItem as Booking;
    }

编辑，

我试过了

 allensCroftEntities1.Attach(ObjectIndex);

编辑，

当我注释掉预订加载事件中的实体时，出现此错误，此代码过去工作正常，但我不知道为什么会出现所有这些问题。

Answer 1

首先尝试将实体附加到上下文:

allensCroftEntities1.Attach(ObjectIndex);
allensCroftEntities1.DeleteObject(ObjectIndex);

或者通过删除该行，使用在类范围内声明的上下文而不是 Bookings_Loaded 事件处理程序中的本地上下文:

WpfApplication7.AllensCroftEntities1 allensCroftEntities1 = new WpfApplication7.AllensCroftEntities1();