CollectionViewSource+PropertyGroupDescription - count of items in a group - wpf

Question

In my WPF application I have a CollectionViewSource which is providing a view to a private ObservableCollection. The CollectionViewSource has a PropertyGroupDescription which is utilised in a ListBox to present data to the User's preference.
Using a ControlTemplate containing a Expander Control within the ListBox GroupStyle, the result is quite nice. However, I would like to show the number of items in each group in the Expander Header in addition to the Group Name. Any ideas on the binding path?
Regards,
Liam
<Style x:Key="basicGroupStyle" TargetType="{x:Type GroupItem}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type GroupItem}">
<Expander Header="{Binding Name}" IsExpanded="True">
<ItemsPresenter/>
</Expander>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
<ListBox ItemsSource="{Binding Source={StaticResource myViewSource}}">
<ListBox.GroupStyle>
<GroupStyle ContainerStyle="{StaticResource basicGroupStyle}"/>
</ListBox.GroupStyle>
</ListBox>

Answer 1

you have to use property ItemCount
<Window x:Class="WpfApplication11.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Window1" Height="300" Width="300">
<Window.Resources>
<XmlDataProvider x:Key="data">
<x:XData>
<Animals xmlns="">
<Animal name="Dory" Species="Fish" />
<Animal name="Felix" Species="Cat" />
<Animal name="Fluffy" Species="Dog" />
<Animal name="Jake" Species="Snake" />
<Animal name="Mittens" Species="Cat" />
<Animal name="Murtle" Species="Turtle" />
<Animal name="Nemo" Species="Fish" />
<Animal name="Rex" Species="Dog" />
<Animal name="Rover" Species="Dog" />
<Animal name="Toonces" Species="Cat" />
</Animals>
</x:XData>
</XmlDataProvider>
<CollectionViewSource x:Key="animalsBySpecies" Source="{Binding Source={StaticResource data}, XPath=Animals/Animal}">
<CollectionViewSource.GroupDescriptions>
<PropertyGroupDescription PropertyName="#Species" />
</CollectionViewSource.GroupDescriptions>
</CollectionViewSource>
</Window.Resources>
<DockPanel>
<ScrollViewer DockPanel.Dock="Bottom" VerticalScrollBarVisibility="Auto">
<ItemsControl ItemsSource="{Binding Source={StaticResource animalsBySpecies}}">
<ItemsControl.GroupStyle>
<GroupStyle>
<GroupStyle.ContainerStyle>
<Style TargetType="{x:Type GroupItem}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type GroupItem}">
<GroupBox >
<GroupBox.Header>
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition></ColumnDefinition>
<ColumnDefinition></ColumnDefinition>
</Grid.ColumnDefinitions>
<TextBlock Text ="{Binding Name}" ></TextBlock>
<TextBlock Text="(" Grid.Column="1" Margin="15,0,0,0"></TextBlock>
<TextBlock Text="{Binding ItemCount}" Grid.Column="1" Margin="20,0,0,0"
HorizontalAlignment="Right" ></TextBlock>
<TextBlock Text=")" Margin="0,0,-5,0" Grid.Column="1
HorizontalAlignment="Right" ></TextBlock>
</Grid>
</GroupBox.Header>
<ItemsPresenter />
</GroupBox>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</GroupStyle.ContainerStyle>
</GroupStyle>
</ItemsControl.GroupStyle>
<ItemsControl.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding XPath=#name}" />
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</ScrollViewer>
</DockPanel>
</Window>

Answer 2

I updated the Group Style as follows. I found that I could not use a MultiBinding in the Expander.Header property, nothing was displayed on screen, I needed to include an intermediate TextBlock instead.
<Style x:Key="basicGroupStyle" TargetType="{x:Type GroupItem}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type GroupItem}">
<Expander IsExpanded="True">
<Expander.Header>
<TextBlock>
<TextBlock.Text>
<MultiBinding StringFormat="{}{0} ({1})">
<Binding Path="Name"/>
<Binding Path="ItemCount"/>
</MultiBinding>
</TextBlock.Text>
</TextBlock>
</Expander.Header>
<ItemsPresenter/>
</Expander>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>