Change Style of Filtered Column Headers

Environment

Product Version	2021.2.511
Product	RadGridView for WPF

Description

How to highlight the header cells of a filtered column.

Solution

To style the header cells of a column after it has been filtered, you can handle the CollectionChanged event of RadGridView's FilterDescriptors collection.

Example 1: Subscribe to the CollectionChanged event

C#

	this.GridView.FilterDescriptors.CollectionChanged += OnFilterDescriptorsCollectionChanged;

In the event handler, you can set the HeaderCellStyle property of the column which was affected by the filtering and remove the style once the filter is cleared.

Example 2: Handle the CollectionChanged event

C#

	private void OnFilterDescriptorsCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
	{
		switch (e.Action)
		{
			case System.Collections.Specialized.NotifyCollectionChangedAction.Add:
				if (e.NewItems.Count == 1)
				{
					var columnFilterDescriptor = e.NewItems[0] as IColumnFilterDescriptor;
					if (columnFilterDescriptor != null)
					{
						var column = columnFilterDescriptor.Column;
						column.HeaderCellStyle = App.Current.Resources["FilteredHeaderCellStyle"] as Style;
					}
				}
				break;
			case System.Collections.Specialized.NotifyCollectionChangedAction.Remove:
				if (e.OldItems.Count == 1)
				{
					var columnFilterDescriptor = e.OldItems[0] as IColumnFilterDescriptor;
					if (columnFilterDescriptor != null)
					{
						var column = columnFilterDescriptor.Column;
						column.HeaderCellStyle = App.Current.Resources["FilteredHeaderCellStyle"] as Style;
					}
				}
				break;
		}
	}

You can then define the FilteredHeaderCellStyle in the way you desire to highlight the header cells. Example 3 demonstrates how to set the Foreground of the affected header cell to Red.

Example 3: Define the style for the affected header cells in App.xaml

XAML

	<Style x:Key="FilteredHeaderCellStyle" TargetType="telerik:GridViewHeaderCell">
		<Setter Property="Foreground" Value="Red"/>
	</Style>

Figure 1: The highlighted header cell of the filtered column