https://stackoverflow.com/questions/15096507
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RussianWhile the responses I got to this were all along the right track, I didn't think any of them really answered my question well enough to be marked as the solution. What I ended up doing was deriving a custom control from the ComboBox (right-click on a ComboBox in the designer and choose Edit Template -> Edit a Copy, this generates a whole bunch of XAML code for the ComboBox template which I copied into the Generic.xaml file of the custom control project I made). I then edited the Popup portion of the generated XAML code to add a WatermarkTextBox (from the Extended WPF Toolkit) above the ItemsPresenter like so:
<Popup x:Name="PART_Popup" AllowsTransparency="true" Grid.ColumnSpan="2" IsOpen="{Binding IsDropDownOpen, RelativeSource={RelativeSource TemplatedParent}}" Margin="1" PopupAnimation="{DynamicResource {x:Static SystemParameters.ComboBoxPopupAnimationKey}}" Placement="Bottom">
<Themes:SystemDropShadowChrome x:Name="Shdw" Color="Transparent" MaxHeight="{TemplateBinding MaxDropDownHeight}" MinWidth="{Binding ActualWidth, ElementName=MainGrid}">
<Border x:Name="DropDownBorder" BorderBrush="{DynamicResource {x:Static SystemColors.WindowFrameBrushKey}}" BorderThickness="1" Background="{DynamicResource {x:Static SystemColors.WindowBrushKey}}">
<ScrollViewer x:Name="DropDownScrollViewer">
<Grid RenderOptions.ClearTypeHint="Enabled">
<Canvas HorizontalAlignment="Left" Height="0" VerticalAlignment="Top" Width="0">
<Rectangle x:Name="OpaqueRect" Fill="{Binding Background, ElementName=DropDownBorder}" Height="{Binding ActualHeight, ElementName=DropDownBorder}" Width="{Binding ActualWidth, ElementName=DropDownBorder}"/>
</Canvas>
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition/>
</Grid.RowDefinitions>
<xtk:WatermarkTextBox Grid.Row="0"
Visibility="{Binding IsDropDownOpen, RelativeSource={RelativeSource TemplatedParent}, Converter={StaticResource booleanToVisibilityConverter}}"
Watermark="Type here to filter..."
Text="{Binding SearchFilter, RelativeSource={RelativeSource TemplatedParent}, UpdateSourceTrigger=PropertyChanged}">
</xtk:WatermarkTextBox>
<ItemsPresenter x:Name="ItemsPresenter" Grid.Row="1" KeyboardNavigation.DirectionalNavigation="Contained" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
</Grid>
</Grid>
</ScrollViewer>
</Border>
</Themes:SystemDropShadowChrome>
</Popup>
The SearchFilter property I'm binding the Text to is a property in my custom control's code-behind which then performs the actual filtering of the values in the ComboBox. It's a little beyond the scope of my original question but here's how I'm doing the filtering in case anyone is curious:
public class SearchableComboBox : ComboBox
{
public const string SearchFilterPropertyName = "SearchFilter";
public readonly static DependencyProperty SearchFilterProperty;
public string SearchFilter
{
get { return (string)GetValue(SearchFilterProperty); }
set { SetValue(SearchFilterProperty, value); }
}
static SearchableComboBox()
{
DefaultStyleKeyProperty.OverrideMetadata(typeof(SearchableComboBox), new FrameworkPropertyMetadata(typeof(SearchableComboBox)));
SearchFilterProperty = DependencyProperty.Register(SearchFilterPropertyName, typeof(string), typeof(SearchableComboBox),
new PropertyMetadata(string.Empty, new PropertyChangedCallback(SearchFilter_PropertyChanged)));
}
private static void SearchFilter_PropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
((SearchableComboBox)d).RefreshFilter();
}
private void RefreshFilter()
{
if (this.ItemsSource != null)
{
ICollectionView view = CollectionViewSource.GetDefaultView(this.ItemsSource);
view.Refresh();
}
}
private bool FilterPredicate(object value)
{
if (value == null)
return false;
if (string.IsNullOrEmpty(SearchFilter))
return true;
return value.ToString().Contains(SearchFilter, StringComparison.CurrentCultureIgnoreCase);
}
protected override void OnItemsSourceChanged(IEnumerable oldValue, IEnumerable newValue)
{
if (newValue != null)
{
ICollectionView view = CollectionViewSource.GetDefaultView(newValue);
view.Filter += this.FilterPredicate;
}
if (oldValue != null)
{
ICollectionView view = CollectionViewSource.GetDefaultView(oldValue);
view.Filter -= this.FilterPredicate;
}
base.OnItemsSourceChanged(oldValue, newValue);
}
