组合框将ItemsSource绑定到与DataGrid相同的对象时，无法向DataGrid添加新行

Question

the concept is,I want a field in record link to other record primarykey
so I have ComboBox in "DataGrid.RowDetailsTemplate"
and bound that ComboBox.ItemsSource to same as DataGrid.ItemsSource
my source code are this

<DataGrid Name="CollectionGrid" AutoGenerateColumns="False" >
    <DataGrid.Columns>
        <DataGridTextColumn Header="Column1" Binding="{Binding ID}"/>
        <DataGridTextColumn Header="Column1" Binding="{Binding Name}"/>
    </DataGrid.Columns>
    <DataGrid.RowDetailsTemplate>
        <DataTemplate>
            <Border Background="Gray" CornerRadius="10">
                <ComboBox ItemsSource="{Binding ElementName=CollectionGrid, Path=ItemsSource}" DisplayMemberPath="Name" SelectedValuePath="Value" SelectedValue="{Binding Ref, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
            </Border>
        </DataTemplate>
    </DataGrid.RowDetailsTemplate>
</DataGrid>

and the code behind

public partial class MainWindow : Window
    {
    public ObservableCollection<PACKET> DB { set; get; }
    public MainWindow()
        {
        InitializeComponent();

        DB = new ObservableCollection<PACKET>();
        DB.Add(new PACKET { ID = 1, Name = "TEST1", Ref = 1});
        DB.Add(new PACKET { ID = 2, Name = "TEST2", Ref = 1 });
        DB.Add(new PACKET { ID = 3, Name = "TEST3", Ref = 1 });

        CollectionGrid.ItemsSource = DB;
        }
    }

public class PACKET
    {
    public Int64 ID  { set; get; }
    public string Name { set; get; }
    public Int64 Ref { set; get; }
    }

the program can showup ComboBox items properly, I can change selected item the problem is when I try to add new row to DataGrid it said

any idea?

Thank you

Answer 1

I don't think it's related to the ComboBox. You can't insert a new row into the table if doing so creates a null PK. Make it an identify column.