WPF Datagrid, is it possible to have a mixture of Groups and plain (non grouped) rows?

Question

I am using WPF Datagrid and have a requirement to show 10,000 rows, hence need virtualization. From several articles on StackOverflow I see that virtualization + grouping is not possible with the WPF Datagrid. This is because the Expander template to render a group cannot be virtualized.

In our system we may have 10,000 rows but only ever 3 or 4 are in each group. Also, the vast majority of rows are not grouped - they have a null GroupId. In a prototype I am working on these render as a group expander with no header. What I'd ideally like is those to be not grouped, just rows, and the rest rendered inside an expander. Is this possible?

Answer 1

try this...

<GroupStyle.ContainerStyle>
    <Style TargetType="{x:Type GroupItem}">
        <Style.Resources>
            <ControlTemplate x:Key="MultiItemGroupTemplate"
                             TargetType="{x:Type GroupItem}">
                <Expander IsExpanded="False">
                    <Expander.Header>
                        <StackPanel Orientation="Horizontal">
                            <TextBlock Text="{Binding Path=Name}" />
                        </StackPanel>
                    </Expander.Header>
                    <ItemsPresenter />
                </Expander>
            </ControlTemplate>
            <ControlTemplate x:Key="SingleItemGroupTemplate"
                             TargetType="{x:Type GroupItem}">
                   <ItemsPresenter />
            </ControlTemplate>
        </Style.Resources>                                
        <Style.Triggers>
            <DataTrigger Binding="{Binding ItemCount}" Value="1">
                <Setter Property="Template"
                        Value="{StaticResource SingleItemGroupTemplate}">
                </Setter>
            </DataTrigger>
        </Style.Triggers>
        <Setter Property="Template"
                Value="{StaticResource MultiItemGroupTemplate}"/>
    </Style>
</GroupStyle.ContainerStyle>

Note: Please note that this will change for DataGrid... DataGrid's ItemPresenter is actually DataGridRowsPresenter