Question

Please help me, I am writing application with “WPF Application Framework” and EF Code First. I’m trying set selected row to ViewModels variable “SelectedRawMaterial” which is binded to DataGrids SelectedItem and it raises an exception : “The current value of the SelectionUnit property on the parent DataGrid prevents rows from being selected.”

private void rawMaterialTable_SelectedCellsChanged(object sender, SelectedCellsChangedEventArgs e)
    {
        DataGridCell cell = null;
        try
        {
            cell = DataGridHelper.GetCell(rawMaterialTable.SelectedCells[0]);
        }
        catch (Exception)
        { }

        if (cell != null)
        {
            int i = DataGridHelper.GetRowIndex(cell);
            try
            {

                RawMaterial rm = (RawMaterial)rawMaterialTable.Items[i];
                ViewModel.SelectedRawMaterial = rm;
            }
            catch (Exception) { }
        }
    }



public static class DataGridHelper
{
    public static DataGridCell GetCell(DataGridCellInfo dataGridCellInfo)
    {
        if (!dataGridCellInfo.IsValid)
        {
            return null;
        }

        var cellContent = dataGridCellInfo.Column.GetCellContent(dataGridCellInfo.Item);
        if (cellContent != null)
        {
            return (DataGridCell)cellContent.Parent;
        }
        else
        {
            return null;
        }
    }

    public static int GetRowIndex(DataGridCell dataGridCell)
    {
        // Use reflection to get DataGridCell.RowDataItem property value.
        PropertyInfo rowDataItemProperty = dataGridCell.GetType().GetProperty("RowDataItem",
                                                                              BindingFlags.Instance |
                                                                              BindingFlags.NonPublic);

        DataGrid dataGrid = GetDataGridFromChild(dataGridCell);

        return dataGrid.Items.IndexOf(rowDataItemProperty.GetValue(dataGridCell, null));
    }

    public static DataGrid GetDataGridFromChild(DependencyObject dataGridPart)
    {
        if (VisualTreeHelper.GetParent(dataGridPart) == null)
        {
            throw new NullReferenceException("Control is null.");
        }
        if (VisualTreeHelper.GetParent(dataGridPart) is DataGrid)
        {
            return (DataGrid)VisualTreeHelper.GetParent(dataGridPart);
        }
        else
        {
            return GetDataGridFromChild(VisualTreeHelper.GetParent(dataGridPart));
        }
    }
}

In this place it raises exception.

ViewModel.SelectedRawMaterial = rm;

DataGrids code

<DataGrid x:Name="rawMaterialTable" ItemsSource="{Binding RawMaterials}" SelectedItem="{Binding SelectedRawMaterial}" 
              CanUserDeleteRows="False" BorderThickness="0" SelectionMode="Single" SelectionUnit="Cell" IsReadOnly="false"
              Grid.Row="1" Grid.Column="1" Margin="1,1,1,1" PreviewKeyDown="rawMaterialTable_PreviewKeyDown" SelectedCellsChanged="rawMaterialTable_SelectedCellsChanged" >
            <DataGrid.InputBindings>
                <KeyBinding Command="{Binding RemoveCommand}" Key="Del"/>
                <KeyBinding Command="{Binding AddCommand}" Key="Insert"/>
                <KeyBinding Command="{Binding EditCommand}" Key="F3"/>
            </DataGrid.InputBindings>

            <DataGrid.Columns>
                <DataGridTextColumn Binding="{Binding Code, UpdateSourceTrigger=PropertyChanged, ValidatesOnDataErrors=True, 
                                  ValidatesOnExceptions=True, NotifyOnValidationError=True}" 
                                Header="{x:Static p:Resources.Code}" Width="60" ElementStyle="{StaticResource TextCellElementStyle}"
                                EditingElementStyle="{StaticResource TextCellEditingStyle}" DisplayIndex="0"/>


            </DataGrid.Columns>
        </DataGrid>

I added SelectionUnit=”Cell” because also I want to handle CellKeyDown.

Answer 1

Its because you have the SelectionUnit (see the definition of the property) property of the data grid set to Cell and I believe you are trying to select a row at a time.

Edited: If you change SelectionUnit to CellOrRowHeader to allow cell selection but the binding to select a whole row