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Controls / RadRichTextBox / Features / Selection
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Selection

Updated on Jan 20, 2026

RadRichTextBox supports not only selection via the UI, but also programmatic selection. This topic shows how you can use both approaches.

UI Selection

The user is able to select the content inside RadRichTextBox in the same way as in MS Word. This is done by clicking on the desired position and dragging to the desired end of the selection. A multiple ranges selection is also allowed. This one is done by holding the Ctrl key while selecting the different ranges.

You can modify the appearance of the selection in the control through the SelectionFill and SelectionStroke properties of RadRichTextBox.

Customize the appearance of the selection

XAML
	<telerik:RadRichTextBox Name="radRichTextBox" SelectionStroke="DarkRed">
	    <telerik:RadRichTextBox.SelectionFill>
	        <SolidColorBrush Color="Red" Opacity="0.5" />
	    </telerik:RadRichTextBox.SelectionFill>
	</telerik:RadRichTextBox>

Customize the appearance of the selection

C#
	this.radRichTextBox.SelectionFill = new System.Windows.Media.SolidColorBrush(Colors.Red); 
	this.radRichTextBox.SelectionFill.Opacity = 0.2;
	this.radRichTextBox.SelectionStroke = System.Windows.Media.Brushes.DarkRed;

Custom selection colors

Customized Selection in RadRichTextBox

Advanced Selection Mode

By default when the user select text the words are selected letter by letter. We have introduced an advanced selection mode that allow you to select whole word automatically. The automatic words selection begins after the selection leaves the first word. This mode can be enabled by the IsAdvancedSelectionEnabled property.

Programmatic Selection

The developer is allowed to manipulate the selection programmatically. This can be used in a lot of scenarios involving editing of the document, or for example, when implementing Search functionality in your RadRichTextBox and you want to select the found string.

The programmatic selection is represented via the DocumentSelection class. The instance of the class gets associated with the RadDocument of RadRichTextBox and allows you to specify selection start and end positions, selection ranges and other. You can manage the selection by either using the Selection property of RadDocument or by creating an instance of the DocumentSelection class.

To learn more about the DocumentPosition read the Positioning topic.

Members of DocumentSelection

Properties:

  • Ranges—Holds a collection of all SelectionRange instances in the selection.
  • IsEmpty—Holds a value determining whether the selection is empty or not.

Methods for manipulating the selection:

  • SelectAll—Selects all the content of the document.
  • SetSelectionStart—Empties the selection and begins a new SelectionRange starting at the specified position. This method starts the creation of a range, which should be finished with the AddSelectionEnd method.
  • AddSelectionStart—Begins a new SelectionRange starting at the specified position. This method starts the creation of a range, which should be finished with the AddSelectionEnd method.
  • AddSelectionEnd—Finishes the started SelectionRange by setting its end.
  • SelectAnnotationRange—Selects annotation range including the AnnotationRangeStart and AnnotationRangeEnd elements.
  • SelectTableRow—Creates a new selection containing the specific table row.
  • SelectTableColumn—Creates a new selection containing all the cells in a table column. There are two overloads that allow you to pass a cell from the column or the table and the grid column index, which should be selected.
  • AddDocumentElementToSelection—Adds a specified document element to the existing selection.
  • AddTableCellToSelection—Adds a table cell to the existing selection.
  • AddParagraphToSelection—Adds a paragraph to the existing selection.

Obtaining information and elements from the selection:

  • CopySelectedDocumentElements—Copies all selected document elements to a DocumentFragment instance.
  • GetSelectedText—Gets the text from the selection. Offers an overload allowing you to specify whether the result should include the bullet or numbering characters in case a paragraph is in a list.
  • GetSelectedParagraphs—Gets the paragraphs included in the selection.
  • GetSelectedBoxes&lt;T&gt;—Enumerates through all inline layout boxes of type T included in the selected ranges.
  • GetFullSelectionGeometry—Gets a System.Windows.Media.Geometry instance describing the form of the selection.
  • GetVisibleSelectionGeometry—Gets a System.Windows.Media.Geometry instance describing the form of the selection visible in the rectangle passed as a parameter.
  • CreateDocumentFromSelection—Creates a new RadDocument instance containing the selected elements.
  • ContainsAnnotationMarkersOfType&lt;T&gt;—Determines whether the selection contains annotation markers of type T.
  • GetAnnotationMarkersOfType&lt;T&gt;—Gets all annotation markers of type T in the selection.
  • GetSelectedSingleInline—Gets the selected Inline if it is the only inline selected, otherwise returns null. This method is suitable to check if only an ImageInline is selected, for example.
  • ToString—Gets the text from the selected document elements.

Clearing the selection method:

  • Clear—Empties the selection.

Events:

  • SelectionChanging—Occurs before the selection is changed.
  • SelectionChanged—Occurs after the selection is changed. Such an event is exposed by the RadRichTextBox class as well.

Select current word

C#
    DocumentPosition startPosition = new DocumentPosition(this.radRichTextBox.Document.CaretPosition);
    DocumentPosition endPosition = new DocumentPosition(startPosition);
    startPosition.MoveToCurrentWordStart();
    endPosition.MoveToCurrentWordEnd();
    this.radRichTextBox.Document.Selection.SetSelectionStart(startPosition);
    this.radRichTextBox.Document.Selection.AddSelectionEnd(endPosition);

The next snippet demonstrates how you can check the content that is selected and select and delete the current paragraph if the text in the selection contains the word "Test".

Select current paragraph and delete it

C#
	string selectedText = this.radRichTextBox.Document.Selection.GetSelectedText();
	
	if (selectedText.Contains("Test"))
	{
	    this.radRichTextBox.Document.Selection.Clear();
	    Paragraph currentParagraph = this.radRichTextBox.Document.CaretPosition.GetCurrentParagraph();
	
	    this.radRichTextBox.Document.Selection.AddDocumentElementToSelection(currentParagraph);
	    this.radRichTextBox.Delete(true);
	}

What is Selection Range?

The selection in RadRichTextBox consists of selection ranges. These ranges are represented by the SelectionRange class which exposes the following members:

  • StartPosition—The position determining the start of the selection range.

  • EndPosition—The position determining the end of the selection range.

  • ContainsPosition—Method that determines whether the range contains a specified DocumentPosition.

  • IsEmpty—Determines whether the range contains any document elements.

  • IsReversed—Returns true when the start position is after the end position. This might be achieved as in code as well as when the user starts dragging the mouse from right to left.

  • IsValid—A range is considered valid when it has valid start and end positions and is not empty.

  • RangeType—When working with ranges, you might need to check what elements are included in a selection range. This could be achieved with the RangeType property of SelectionRange. This property is of type SelectionRangeType and could have one of the following values:

  • Composite—Represents selection range with mixed elements.

  • Table—SelectionRange, which contains a Table.

  • TableRow—The range consists of a TableRow.

  • TableCell—TableCell selection range.

Check the type of the elements inside the selection

C#
	SelectionRange selectionRange = this.radRichTextBox.Document.Selection.Ranges.First();
	if (selectionRange.RangeType == SelectionRangeType.Table)
	{
	    SetTableProperties();
	}

Multi-Range Selection

You can implement multi-range Selection by either calling multiple times the AddSelectionStart and AddSelectionEnd methods of the DocumentSelection class or by working with the Ranges collection.

Here is an example of how you can use the first approach.

Select all occurrences of the "RadRichTextBox" word

C#
	DocumentPosition position = new DocumentPosition(this.radRichTextBox.Document);
	do
	{
	    //GetCurrentSpan().Text returns the word at the position
	    string word = position.GetCurrentSpanBox().Text;
	    if (word.Contains("RadRichTextBox"))
	    {
	        DocumentPosition wordEndPosition = new DocumentPosition(position);
	        wordEndPosition.MoveToCurrentWordEnd();
	        this.radRichTextBox.Document.Selection.AddSelectionStart(position);
	        this.radRichTextBox.Document.Selection.AddSelectionEnd(wordEndPosition);
	
	    }
	} 
	while (position.MoveToNextWordStart());

Multiple selection in RadRichTextBox

Selection in RadRichTextBox

Mouse Selection Settings

  • MouseSelectionHandler.DoubleClickTime—This static property controls the double click speed of the RichTextBox. The default value is 400ms. It is different from the default value in .NET which is 500ms. This property allows you to set the value that best suits your case. You can set it in your code usually when initializing the RichTextBox control.

  • MouseSelectionHandler.MouseDragThreshold—This static property controls the number of pixels that the mouse needs to travel so that the action is considered a drag operation. The default value is 3.

  • MouseSelectionHandler.MouseDoubleClickThreshold—This static property controls the number of pixels that are allowed for the mouse to move when double-clicking. The default value of this property is 1.

Customizing Keyboard Shift Selection

The keyboard selection that happens on Shift + arrow keys press can be customized by creating a custom KeyboardSelectionHandler. The handler is assigned to the KeyboardSelectionHandler property of the ActiveEditorPresenter of RadRichTextBox.

The selection handler allows you to override the MoveActiveEnd method, which is invoked on selection when using the Shift key.

Creating custom KeyboardSelectionHandler

C#
	public class CustomSelectionHandler : KeyboardSelectionHandler
	{
		public CustomSelectionHandler(RadDocument document) : base(document)
		{
		}

		public override void MoveActiveEnd(NavigationUnit unit, Direction direction)
		{
			base.MoveActiveEnd(unit, direction);
			
			RadDocument document = this.Document;
			DocumentPosition position = document.CaretPosition;
			// update the document position
		}
	}

Assigning the custom KeyboardSelectionHandler

C#
	private void RadRichTextBox_Loaded(object sender, RoutedEventArgs e)
	{
		var documentPresenter = (DocumentPresenterBase)this.radRichTextBox.ActiveEditorPresenter;
		documentPresenter.KeyboardSelectionHandler = new CustomSelectionHandler(this.radRichTextBox.Document);
	}

Customizing Mouse Selection Behavior

The mouse selection behavior in the RichTextBox control can be customized by creating a class that derives from MouseSelectionHandler and override its methods. The custom handler, can be assigned to the MouseSelectionHandler property of the ActiveEditorPresenter of RadRichTextBox.

The following example shows how to implement a custom selection handler which selects specific words on a single click.

Creating custom MouseSelectionHandler

C#
	public class CustomMouseSelectionHandler : MouseSelectionHandler
	{
		RadDocument currentDocument;
		private List<string> predefinedSingleClickWords;

		internal List<string> PredefinedSingleClickWords
		{
			get 
			{
				if (predefinedSingleClickWords == null)
				{
					predefinedSingleClickWords = new List<string>();
				}
				return predefinedSingleClickWords; 
			}
		}

		public CustomMouseSelectionHandler(RadDocument document, DocumentPresenterBase presenter)
			: base(document, presenter)
		{
			currentDocument = document;
		}

		public override void RegisterDocumentMouseUp(SourceType source = SourceType.Mouse, Point? position = null)
		{
			base.RegisterDocumentMouseUp(source, position);
			TrySelectWordUnderMouse();
		}

		public bool TrySelectWordUnderMouse()
		{
			var position = currentDocument.CaretPosition;
			var clickedInlineBox = position.GetCurrentInlineBox();

			if (predefinedSingleClickWords.Any(x => x.ToLower().Equals(clickedInlineBox.Text.ToLower())))
			{
				DocumentPosition startPosition = new DocumentPosition(position);
				DocumentPosition endPosition = new DocumentPosition(startPosition);
				startPosition.MoveToCurrentWordStart();
				endPosition.MoveToCurrentWordEnd();
				this.currentDocument.Selection.SetSelectionStart(startPosition);
				this.currentDocument.Selection.AddSelectionEnd(endPosition);
				return true;
			}
			return false;
		}

		// Below you can see other methods that can be overridden:

		protected override void RegisterDocumentMultipleMouseDown(bool ctrlPressed, bool shiftPressed, Point position)
		{
			base.RegisterDocumentMultipleMouseDown(ctrlPressed, shiftPressed, position);
		}

		public override void RegisterDocumentMouseRightButtonDown(UIElement originalSource, SourceType source = SourceType.Mouse)
		{
			base.RegisterDocumentMouseRightButtonDown(originalSource, source);
		}

		public override void RegisterDocumentMouseDown(bool ctrlPressed, bool shiftPressed, Point position, UIElement originalSource = null, SourceType source = SourceType.Mouse)
		{
			base.RegisterDocumentMouseDown(ctrlPressed, shiftPressed, position, originalSource, source);
		}

		public override void RegisterDocumentMouseMove(Point position, SourceType source = SourceType.Mouse)
		{
			base.RegisterDocumentMouseMove(position, source);
		}

		protected override void RegisterDocumentSingleMouseDown(bool ctrlPressed, bool shiftPressed, Point position, UIElement originalSource)
		{
			base.RegisterDocumentSingleMouseDown(ctrlPressed, shiftPressed, position, originalSource);
		}
	}

Assigning the custom MouseSelectionHandler

C#
	private void RadRichTextBox_Loaded(object sender, RoutedEventArgs e)
	{
		UpdateMouseSelectionHandler((RadRichTextBox)sender);
	}

	private void RadRichTextBox_DocumentChanged(object sender, EventArgs e)
	{
		UpdateMouseSelectionHandler((RadRichTextBox)sender);
	}

	private void UpdateMouseSelectionHandler(RadRichTextBox rtb)
	{
		var presenter = rtb.ActiveEditorPresenter as DocumentPresenterBase;
		if (presenter != null)
		{
			var selectionHandler = new CustomMouseSelectionHandler(rtb.Document, presenter);
			selectionHandler.PredefinedSingleClickWords.Add("Telerik");
			selectionHandler.PredefinedSingleClickWords.Add("Microsoft");
			selectionHandler.PredefinedSingleClickWords.Add("NET");
			presenter.MouseSelectionHandler = selectionHandler;
		}
	}

See Also

In this article
UI SelectionAdvanced Selection ModeProgrammatic SelectionMembers of DocumentSelectionWhat is Selection Range?Multi-Range SelectionMouse Selection SettingsCustomizing Keyboard Shift SelectionCustomizing Mouse Selection BehaviorSee Also
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