Hi I have a problem in display selected item of combo box in a data grid. in this code nothing show in combo box as selected item.

this is my xaml :

                                        <DataGridTemplateColumn.CellTemplate>
                                            <DataTemplate>
                                                <ComboBox ItemsSource="{Binding DataContext.GridTypes, RelativeSource={RelativeSource AncestorType=Window}}"
                                                          SelectedItem="{Binding GridType, Mode=TwoWay}"
                                                          DisplayMemberPath="Name"
                                                          Style="{StaticResource ComboBoxFlatStyle}"/>
                                            </DataTemplate>
                                        </DataGridTemplateColumn.CellTemplate>
                                    </DataGridTemplateColumn>

this is my code behind:

        public DatumManagerMainWindow(Models.DatumManager datumManager)
        {
            InitializeComponent();

            MainWindowViewModel mainViewModel = new MainWindowViewModel(datumManager);

            this.DataContext = mainViewModel;

            dtg_xGrids.ItemsSource = mainViewModel.HorizontalGrids;
            dtg_yGrids.ItemsSource = mainViewModel.VerticalGrids;

        }

and this is my view model:

    internal class MainWindowViewModel
    {
        public ObservableCollection<DatumGrid> HorizontalGrids { get; set; }
        public ObservableCollection<DatumGrid> VerticalGrids { get; set; }
        public ObservableCollection<DatumLevel> Levels { get; set; }
        public ObservableCollection<DatumGridType> GridTypes { get; set; }  // Add this property

        public MainWindowViewModel(Models.DatumManager datumManager)
        {
            var datumSystem = datumManager.GetDatumSystem();
            HorizontalGrids = datumSystem.HorizontalGrids;
            VerticalGrids = datumSystem.VerticalGrids;
            Levels = datumSystem.Levels;

            GridTypes = datumManager.GetDatumGridTypes();

        }
    }

and this is my model:

    public class DatumGrid : Datum
    {
        public int Id { get; }
        public string Name { get; set; }
        public DatumGridType GridType { get; set; }
        public DatumGridDirection Direction { get; }
        public double Ordinate { get; set; }

        public DatumGrid(int id, string name, DatumGridType gridType, DatumGridDirection direction, double ordinate)
        {
            Id = id;
            Name = name;
            GridType = gridType;
            Direction = direction;
            Ordinate = ordinate;
        }
    }

and i want to display name of DatumGridType with this class:

    public class DatumGridType
    {
        public int Id { get; }
        public string Name { get; }
        public DatumGridType( int id,string name) 
        {            
            Id = id;
            Name = name;
        }
    }

please help me . thanks

I can see any selected item in my combo boxes.