WPF - Maintain Group Style in ListView

Question

I've got a simple ListView which pulls data from an ObservableCollection and I'm using a CollectionViewSource to a set a GroupPropertyDescription so that my rows appear grouped. I've used the following style to use an expander for each group:

<Style TargetType="{x:Type GroupItem}" x:Key="listViewGroupStyle">
    <Setter Property="Margin" Value="0 0 0 5" />
    <Setter Property="Template" >
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type GroupItem}">
                <Expander IsExpanded="False" BorderBrush="{Binding Name, Converter={StaticResource statusForegroundConverter}}" BorderThickness="2" Margin="1">
                    <Expander.Header>
                        <Border BorderThickness="3" BorderBrush="{Binding Name, Converter={StaticResource statusBackgroundConverter}}" CornerRadius="6">
                            <DockPanel TextBlock.FontWeight="Bold" TextBlock.Foreground="{Binding Name, Converter={StaticResource statusForegroundConverter}}">
                                <TextBlock Text="{Binding Name, Converter={StaticResource statusStringConverter}}" Margin="5 2 2 2" />
                                <TextBlock Text=" - " Margin="2" />
                                <TextBlock Text="{Binding Path=ItemCount}" Margin="0 2 5 2"/>
                            </DockPanel>
                        </Border>
                    </Expander.Header>
                    <Expander.Content>
                        <ItemsPresenter />
                    </Expander.Content>
                </Expander>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

The problem I have is that my collection is updated frequently during runtime and everytime it is, all the groups get collapsed regardless of whether or not I had some open.

Is there a way for me to maintain the appearance of the ListView after my collection has been reassigned?

Answer 1

I've found a solution, with most of the details here:

http://social.msdn.microsoft.com/Forums/en/wpf/thread/f022425b-f685-4a7a-91df-828103871ebc

The main point is that when an ItemsSource is reassigned, it invalidates the associated control, causing it to redraw. However, as I was using an ObservableCollection, it's far easier to accumulate your new data in a temporary list and add or remove objects from the original list as necessary:

ObservableCollection<xxx> tempBuilds = new ObservableCollection<xxx>();

IEnumerable<xxx> addRange = tempBuilds.Except(_filteredBuilds);
IEnumerable<xxx> removeRange = _filteredBuilds.Except(tempBuilds);

addRange.ToList().ForEach(bm => _filteredBuilds.Add(bm));
removeRange.ToList().ForEach(bm => _filteredBuilds.Remove(bm));