Question

I have a DataGridComboBoxColum in a DataGrid.
I would like to be able to click on the cell one time and have the combobox drop down. Currently I have to click multiple times.

  <DataGrid AutoGenerateColumns="False" Height="148" HorizontalAlignment="Left" Margin="48,85,0,0" Name ="dg_display" VerticalAlignment="Top" Width="645"  CanUserAddRows="False" CanUserDeleteRows="False" ItemsSource="{Binding}" SelectionChanged="DgDisplaySelectionChanged">
        <DataGrid.Columns>
            <DataGridTextColumn IsReadOnly="True" Header="Symbol" Binding="{Binding Symbol}" />
            <DataGridTextColumn IsReadOnly="True" Header="Company ID" Binding="{Binding CompanyID}" />
            <DataGridComboBoxColumn IsReadOnly="False" Header="Sector" SelectedValueBinding="{Binding Sector}" DisplayMemberPath="{Binding [0]}" Visibility="Visible" >
                <DataGridComboBoxColumn.EditingElementStyle>
                    <Style TargetType="ComboBox">
                        <Setter Property="ItemsSource" Value="{Binding SectorList}" />
                    </Style>
                </DataGridComboBoxColumn.EditingElementStyle>
                <DataGridComboBoxColumn.ElementStyle>
                    <Style TargetType="ComboBox">
                        <Setter Property="ItemsSource" Value="{Binding SectorList}" />
                    </Style>
                </DataGridComboBoxColumn.ElementStyle>
            </DataGridComboBoxColumn>
        </DataGrid.Columns>
    </DataGrid>

Answer 1

One-click DataGridComboBoxColumn editing + one click CheckboxColumn editing

See also:
https://stackoverflow.com/a/8333704/724944

XAML:

        <Style TargetType="{x:Type DataGridCell}">
            <EventSetter Event="PreviewMouseLeftButtonDown" Handler="DataGridCell_PreviewMouseLeftButtonDown" />
            <EventSetter Event="PreviewTextInput" Handler="DataGridCell_PreviewTextInput" />
        </Style>

Code-behind:

    private void DataGridCell_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    {
        DataGridCell cell = sender as DataGridCell;
        GridColumnFastEdit(cell, e);
    }

    private void DataGridCell_PreviewTextInput(object sender, TextCompositionEventArgs e)
    {
        DataGridCell cell = sender as DataGridCell;
        GridColumnFastEdit(cell, e);
    }

    private static void GridColumnFastEdit(DataGridCell cell, RoutedEventArgs e)
    {
        if (cell == null || cell.IsEditing || cell.IsReadOnly)
            return;

        DataGrid dataGrid = FindVisualParent<DataGrid>(cell);
        if (dataGrid == null)
            return;

        if (!cell.IsFocused)
        {
            cell.Focus();
        }

        if (cell.Content is CheckBox)
        {
            if (dataGrid.SelectionUnit != DataGridSelectionUnit.FullRow)
            {
                if (!cell.IsSelected)
                    cell.IsSelected = true;
            }
            else
            {
                DataGridRow row = FindVisualParent<DataGridRow>(cell);
                if (row != null && !row.IsSelected)
                {
                    row.IsSelected = true;
                }
            }
        }
        else
        {
            ComboBox cb = cell.Content as ComboBox;
            if (cb != null)
            {
                //DataGrid dataGrid = FindVisualParent<DataGrid>(cell);
                dataGrid.BeginEdit(e);
                cell.Dispatcher.Invoke(
                 DispatcherPriority.Background,
                 new Action(delegate { }));
                cb.IsDropDownOpen = true;
            }
        }
    }


    private static T FindVisualParent<T>(UIElement element) where T : UIElement
    {
        UIElement parent = element;
        while (parent != null)
        {
            T correctlyTyped = parent as T;
            if (correctlyTyped != null)
            {
                return correctlyTyped;
            }

            parent = VisualTreeHelper.GetParent(parent) as UIElement;
        }
        return null;
    }