WPF ListView with CollectionViewSource not getting SelectedItem in ViewModel

Question

I Have a ListView I am grouping using a CollectionViewSource, but I cant seem to get the selected item back into the ViewModel. What do I need to do to get the item the user selects? SelectedItem="{Binding SelectedComparatorGroupItem}" does not appear to work when using a collectionviewSource, I tried IsSynchronizedWithCurrentItem="True" but that did not help.

                <Grid>
                    <Grid.Resources>
                        <CollectionViewSource x:Key="NumberGroups"
                                              Source="{Binding Path=ComparatorGroupItemList}">
                            <CollectionViewSource.GroupDescriptions>
                                <PropertyGroupDescription PropertyName="Group" />
                            </CollectionViewSource.GroupDescriptions>
                        </CollectionViewSource>
                    </Grid.Resources>
                    <ListView x:Name="lvNumbers"
                              DataContext="{StaticResource NumberGroups}"
                              ItemsSource="{Binding IsAsync=True}"
                              IsSynchronizedWithCurrentItem="True"
                              SelectedItem="{Binding SelectedComparatorGroupItem}"
                              VirtualizingPanel.IsContainerVirtualizable="True"
                              VirtualizingPanel.IsVirtualizing="True"
                              VirtualizingPanel.IsVirtualizingWhenGrouping="True">           
                          
                        <ListView.View>
                            <GridView>
                                <GridViewColumn Header="Number" DisplayMemberBinding="{Binding Number}"/>
                                <GridViewColumn Header="# Found" DisplayMemberBinding="{Binding NumberFound}"/>
                            </GridView>
                        </ListView.View>
                        <ListView.GroupStyle>
                            <GroupStyle>
                                <GroupStyle.ContainerStyle>
                                    <Style TargetType="{x:Type GroupItem}">
                                        <Setter Property="Template">
                                            <Setter.Value>
                                                <ControlTemplate>
                                                    <Expander IsExpanded="False">
                                                        <Expander.Header>
                                                            <StackPanel Orientation="Horizontal">
                                                                <TextBlock Text="{Binding Name}"
                                                                           Margin="3"
                                                                           FontSize="18" FontWeight="Bold"
                                                                           />
                                                                <TextBlock Text="{Binding ItemCount}"
                                                                           Margin="3"
                                                                           FontSize="18" FontWeight="Bold"
                                                                           />
                                                            </StackPanel>
                                                        </Expander.Header>
                                                        <ItemsPresenter/>
                                                    </Expander>
                                                </ControlTemplate>
                                            </Setter.Value>
                                        </Setter>
                                    </Style>
                                </GroupStyle.ContainerStyle>
                            </GroupStyle>
                        </ListView.GroupStyle>
                    </ListView>
                </Grid>

Answer 1

You set the DataContext of the ListView to your local CollectionViewSource. That means that binding SelectedItem to SelectedComparatorGroupItem is going to look for the SelectedComparatorGroupItem property on the CollectionViewSource, not your viewmodel. You should be seeing some kind of binding error in the output window from that.

Don't set the DataContext, just let it flow through naturally. All you should need to do is bind the ItemsSource to the CollectionViewSource.

I think this will do it, but I don't have VS open, or access to your ViewModel, to verify:

<ListView x:Name="lvNumbers"
    ItemsSource="{Binding Source={StaticResource NumberGroups}, IsAsync=True}"
    IsSynchronizedWithCurrentItem="True"
    SelectedItem="{Binding SelectedComparatorGroupItem}"
    VirtualizingPanel.IsContainerVirtualizable="True"
    VirtualizingPanel.IsVirtualizing="True"
    VirtualizingPanel.IsVirtualizingWhenGrouping="True"> 

As a general rule, if you are ever setting the DataContext of something, you are not doing the way WPF wants you to do it. Usually the only place I end up setting it is when I am being lazy with a UserControl.