Why does ObservableCollection throws an exception when being modified?

Question

My application uses a WPF DataGrid. One of the columns is a template column that contains a ComboBox bound to an ObservableCollection

Answer 1

Finally I found the reason for the exception. The problem occurs when you are removing the selected item from the list. Below I've posted an incomplete piece of code.

<!-- XAML -->
<ListBox ItemsSource="{Binding Rooms}" SelectedItem="{Binding SelectedRoom}">
    <ListBox.ItemTemplate>
        <DataTemplate>
            <DockPanel>
                <Button Content="remove" DockPanel.Dock="Right" Command="{Binding Some Remove Command}" />
                <TextBlock Text="{Binding Name}" />
            </DockPanel>
        </DataTemplate>
    </ListBox.ItemTemplate>
</ListBox>

And the view model:

// View Model
public ObservableCollection<Room> Rooms { get; private set; }
public Room SelectedRoom { get; set; }

public RemoveRoom()
{
    var room = SelectedRoom;
    //SelectedRoom = null; // Uncomment this line to avoid the exception

    Rooms.Remove(room);
}

The solution is to first set the selected item to null (or any other item) before actually removing the item from the list.

Oliver Hanappi

Answer 2

Is your Room class object actually instantiated? It looks as if your adding an uninitialised value.