Hiding expander when all content is collapsed

Question

I have A WPF Datagrid that has a Collection View Source with 3 levels of grouping on it.

I have styled the datagrid to use 3 expanders such that it looks like this:

Level 1 Expander
<content>
    Level 2 Expander
    <content>
        Level 3 Expander
        <content>

Level 2 and Level 1 are just title of the groups

I have a second control that allows the user to show and hide level 3 items which works by binding the Level 3 expander to a Boolean "IsVisible" property in the object behind.

       <!--  Style for groups under the top level. this is the style for how a sample is displayed  -->
        <GroupStyle>
            <GroupStyle.ContainerStyle>
                <Style TargetType="{x:Type GroupItem}">
                    <Setter Property="Margin" Value="0,0,0,0" />
                    <Setter Property="Template">
                        <Setter.Value>
                            <ControlTemplate TargetType="{x:Type GroupItem}">

                                <!--  The parent control that determines whether or not an item needs to be displayed. This holds all of the sub controls displayed for a sample  -->
                                <Expander Margin="2"
                                          Background="{Binding Path=Name,
                                                               Converter={StaticResource SampleTypeToColourConverter}}"
                                          IsExpanded="True"
                                          Visibility="{Binding Path=Items[0].IsVisibleInMainScreen,
                                                               Converter={StaticResource BoolToVisibilityConverter}}">

This approach works fantasically well.

HOWEVER

If the user deselects all items in a level 3 expander, the Level 2 expander header still displays meaning that valuable real estate is used up showing the header of a group with no visible data.

What I would like is a way to bind the visibility of the level 2 expander to its child controls and say "If all children are visible then show the expander, otherwise collapse it"

Is this possible?

Answer 1

I found a rather simple and clean way, yet not perfect, to achieve your goal. This should do the trick if hou don't have too much groups.

I've just added this trigger to the GroupItem ControlTemplate :

<ControlTemplate.Triggers>
    <DataTrigger Binding="{Binding ElementName=IP, Path=ActualHeight}" Value="0">
        <Setter Property="Visibility" Value="Hidden"/>
        <Setter Property="Height" Value="1"/>
    </DataTrigger>
</ControlTemplate.Triggers>

When the ItemsPresenter (IP) ActualSize drops to zero, it Will almost collapse the header.

Why almost ?

When the control gets initialized and before the binding occurs, the ItemPresenter ActualHeight is 0 and when Visibility is set to Collapsed, the ItemPresenter doesn't get rendered at all.

Using Visibility.Hidden allows the ItemsPresenter to go to the render phase and be mesured. I succedeed to drop Height to .4 px but I suspect this to be device dependant.