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    The following example demonstrates how to use a ComboBox as an auto-filter control to automatically filter the content of the ShipCountry column. ComboBox controls do not support multiple selections; therefore, the values of the target column will only be filtered by 1 value.

    Since, by default, the auto-filter control in the column-manager-cell drop downs support multiple selections, it is recommended to deactivate the drop down by setting the AllowAutoFilter property of the ColumnManagerRow to false to hide the column-manager cells' auto-filter controls and prevent unexpected synchronization behavior between the controls that have the same auto-filter target column or different selection modes.

    XAML
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    <Grid>
  <Grid.Resources>
    <xcdg:DataGridCollectionViewSource x:Key="cvsOrders"
                                       Source="{Binding Source={x:Static Application.Current},Path=Orders}"
                                       AutoFilterMode="And"
                                       AutoCreateItemProperties="False"
                                       DefaultCalculateDistinctValues="False"
                                       DistinctValuesConstraint="Filtered"
                                       DistinctValuesRefreshNeeded="cvsOrders_DistinctValuesRefreshNeeded">
      <xcdg:DataGridCollectionViewSource.ItemProperties>
        <xcdg:DataGridItemProperty Name="ShipCountry"
                                   Title="Country"
                                   CalculateDistinctValues="True" />
        <xcdg:DataGridItemProperty Name="ShipCity"
                                   Title="City"
                                   CalculateDistinctValues="True" />
        <xcdg:DataGridItemProperty Name="ShipAddress"
                                   Title="Address" />
        <xcdg:DataGridItemProperty Name="ShipPostalCode"
                                   Title="Postal Code" />
        <xcdg:DataGridItemProperty Name="ShipName"
                                   Title="Name" />
        <xcdg:DataGridItemProperty Name="OrderDate"
                                   Title="Order Date" />
        <xcdg:DataGridItemProperty Name="Freight" />
      </xcdg:DataGridCollectionViewSource.ItemProperties>
    </xcdg:DataGridCollectionViewSource>
  </Grid.Resources>
  <DockPanel>
    <StackPanel Margin="20,0,0,0"
                Orientation="Horizontal"
                DockPanel.Dock="Top"
                HorizontalAlignment="Left">
      <xcdg:AutoFilterControl x:Name="ShipCountryAutoFilterControl"
                              AutoFilterColumn="{Binding ElementName=dataGrid, Path=Columns[ShipCountry]}"
                              AutoFilterContext="{Binding ElementName=dataGrid, Path=DataGridContext}">
        <xcdg:AutoFilterControl.Template>
          <ControlTemplate TargetType="{x:Type xcdg:AutoFilterControl}">
            <StackPanel>
              <Button Content="Clear Country filter"
                      Command="xcdg:AutoFilterControl.ClearAutoFilterValues"
                      CommandTarget="{Binding ElementName=ShipCountryAutoFilterControl}" />
              <ComboBox x:Name="PART_DistinctValuesHost"
                        DropDownOpened="ShipCountryAutoFilterControl_DropDownOpened" />
            </StackPanel>
          </ControlTemplate>
        </xcdg:AutoFilterControl.Template>
      </xcdg:AutoFilterControl>
      <xcdg:AutoFilterControl x:Name="ShipCityAutoFilterControl"
                              AutoFilterColumn="{Binding ElementName=dataGrid, Path=Columns[ShipCity]}"
                              AutoFilterContext="{Binding ElementName=dataGrid, Path=DataGridContext}">
        <xcdg:AutoFilterControl.Template>
          <ControlTemplate TargetType="{x:Type xcdg:AutoFilterControl}">
            <StackPanel>
              <Button Content="Clear City filter"
                      Command="xcdg:AutoFilterControl.ClearAutoFilterValues"
                      CommandTarget="{Binding ElementName=ShipCityAutoFilterControl}" />
              <ComboBox x:Name="PART_DistinctValuesHost"
                        DropDownOpened="ShipCityAutoFilterControl_DropDownOpened" />
            </StackPanel>
          </ControlTemplate>
        </xcdg:AutoFilterControl.Template>
      </xcdg:AutoFilterControl>
    </StackPanel>
    <xcdg:DataGridControl x:Name="dataGrid"
                          ItemsSource="{Binding Source={StaticResource cvsOrders}}">
      <xcdg:DataGridControl.View>
        <xcdg:TableflowView UseDefaultHeadersFooters="False">
          <xcdg:TableflowView.FixedHeaders>
            <DataTemplate>
              <xcdg:GroupByControl />
            </DataTemplate>
            <DataTemplate>
              <xcdg:ColumnManagerRow AllowAutoFilter="False" />
            </DataTemplate>
          </xcdg:TableflowView.FixedHeaders>
        </xcdg:TableflowView>
      </xcdg:DataGridControl.View>
    </xcdg:DataGridControl>
  </DockPanel>
</Grid>

    The following code provides the code-behind implementation of the DistinctValuesRefreshNeeded and DropDownOpened events.

    public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
        //Reset all flags
        m_distinctValuesNeedRefreshFlags.Add("ShipCountry", false);
        m_distinctValuesNeedRefreshFlags.Add("ShipCity", false);
    }
    private void cvsOrders_DistinctValuesRefreshNeeded(object sender, EventArgs e)
    {
        //Use this event to set flags that will tell the AutoFilterControl it needs to update when its DropDown is opening.
        IList<string> keys = m_distinctValuesNeedRefreshFlags.Keys.ToList();
        for (int i = 0; i < keys.Count; i++)
        {
            m_distinctValuesNeedRefreshFlags[keys[i]] = true;
        }
    }
    private void ShipCountryAutoFilterControl_DropDownOpened(object sender, EventArgs e)
    {
        //If DistinctValues need to be updated
        if (m_distinctValuesNeedRefreshFlags["ShipCountry"])
        {
            //Get the collection view
            DataGridCollectionView collectionView = dataGrid.ItemsSource as DataGridCollectionView;
            if (collectionView != null)
            {
                //And refresh the DistinctValues only for the required field
                collectionView.RefreshDistinctValuesForFieldName("ShipCountry");
            }
            //Reset the flag.
            m_distinctValuesNeedRefreshFlags["ShipCountry"] = false;
        }
    }
    private void ShipCityAutoFilterControl_DropDownOpened(object sender, EventArgs e)
    {
        //If DistinctValues need to be updated
        if (m_distinctValuesNeedRefreshFlags["ShipCity"])
        {
            //Get the collection view
            DataGridCollectionView collectionView = dataGrid.ItemsSource as DataGridCollectionView;
            if (collectionView != null)
            {
                //And refresh the DistinctValues only for the required field
                collectionView.RefreshDistinctValuesForFieldName("ShipCity");
            }
            //Reset the flag.
            m_distinctValuesNeedRefreshFlags["ShipCity"] = false;
        }
    }
    private Dictionary<string, bool> m_distinctValuesNeedRefreshFlags = new Dictionary<string, bool>();
}
    Public Partial Class MainWindow
 Inherits Window
 Public Sub New()
  InitializeComponent()
  'Reset all flags
  m_distinctValuesNeedRefreshFlags.Add("ShipCountry", False)
  m_distinctValuesNeedRefreshFlags.Add("ShipCity", False)
 End Sub
 Private Sub cvsOrders_DistinctValuesRefreshNeeded(sender As Object, e As EventArgs)
  'Use this event to set flags that will tell the AutoFilterControl it needs to update when its DropDown is opening.
  Dim keys As IList(Of String) = m_distinctValuesNeedRefreshFlags.Keys.ToList()
  For i As Integer = 0 To keys.Count - 1
   m_distinctValuesNeedRefreshFlags(keys(i)) = True
  Next
 End Sub
 Private Sub ShipCountryAutoFilterControl_DropDownOpened(sender As Object, e As EventArgs)
  'If DistinctValues need to be updated
  If m_distinctValuesNeedRefreshFlags("ShipCountry") Then
   'Get the collection view
   Dim collectionView As DataGridCollectionView = TryCast(dataGrid.ItemsSource, DataGridCollectionView)
   If collectionView IsNot Nothing Then
    'And refresh the DistinctValues only for the required field
    collectionView.RefreshDistinctValuesForFieldName("ShipCountry")
   End If
   'Reset the flag.
   m_distinctValuesNeedRefreshFlags("ShipCountry") = False
  End If
 End Sub
 Private Sub ShipCityAutoFilterControl_DropDownOpened(sender As Object, e As EventArgs)
  'If DistinctValues need to be updated
  If m_distinctValuesNeedRefreshFlags("ShipCity") Then
   'Get the collection view
   Dim collectionView As DataGridCollectionView = TryCast(dataGrid.ItemsSource, DataGridCollectionView)
   If collectionView IsNot Nothing Then
    'And refresh the DistinctValues only for the required field
    collectionView.RefreshDistinctValuesForFieldName("ShipCity")
   End If
   'Reset the flag.
   m_distinctValuesNeedRefreshFlags("ShipCity") = False
  End If
 End Sub
 Private m_distinctValuesNeedRefreshFlags As New Dictionary(Of String, Boolean)()
End Class