Mark the text control as being changed to prevent any text content or selection changed events : TextBox « Windows Presentation Foundation « VB.Net Tutorial

1. VB.Net Tutorial
2. Windows Presentation Foundation
3. TextBox

<Window 
  x:Class="WpfApplication1.Window1"
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  Title="Window1" Height="600" Width="800">
  <DockPanel>
    <StackPanel DockPanel.Dock="Bottom" Orientation="Horizontal">
      <TextBox x:Name="tbxInsertionText" Width="200" Margin="5,0" />
      <Button DockPanel.Dock="Bottom" Content="Insert" Click="btnInsert_Click"/>
    </StackPanel>
    <RichTextBox x:Name="rtbTextContent" />
  </DockPanel>
</Window>
//File:Window.xaml.vb
Imports System.Windows
Imports System.Windows.Documents
Imports System.Windows.Input

Namespace WpfApplication1
  Public Partial Class Window1
    Inherits Window
    Public Sub New()
      InitializeComponent()
    End Sub

    Private Sub btnInsert_Click(sender As Object, e As RoutedEventArgs)
      If String.IsNullOrEmpty(tbxInsertionText.Text) Then
        Return
      End If
      rtbTextContent.BeginChange()
      If rtbTextContent.Selection.Text <> String.Empty Then
        rtbTextContent.Selection.Text = String.Empty
      End If
      Dim tp As TextPointer = rtbTextContent.CaretPosition.GetPositionAtOffset(0, LogicalDirection.Forward)
      rtbTextContent.CaretPosition.InsertTextInRun(tbxInsertionText.Text)
      rtbTextContent.CaretPosition = tp
      rtbTextContent.EndChange()
      Keyboard.Focus(rtbTextContent)
    End Sub
  End Class
End Namespace

16.4.TextBox
	16.4.1.	You cannot use TextBox and Image at the same time for Button Content
	16.4.2.	Single line and Multiline TextBox
	16.4.3.	TextBox Column
	16.4.4.	Bind value to TextBox
	16.4.5.	An upside down TextBox
	16.4.6.	Style with Data Trigger for TextBox
	16.4.7.	TextBox with custom ErrorTemplate and ToolTip
	16.4.8.	TextBox uses the ExceptionValidationRule and UpdateSourceExceptionFilter handler
	16.4.9.	TextBox with UpdateSourceExceptionFilter handler
	16.4.10.	TextBox focus listener
	16.4.11.	TextBox MouseLeftButtonDown action and PreviewMouseLeftButtonDown action
	16.4.12.	Mark the text control as being changed to prevent any text content or selection changed events
	16.4.13.	Listen to TextBox text changed event
	16.4.14.	Handler for the PreviewKeyDown event on the TextBox
	16.4.15.	Format TextBox with MenuItem: normal, bold, italic
	16.4.16.	TextBox: set text, select all, clear, prepend, insert, append, cut, paste, undo
	16.4.17.	Set TextBox to editable
	16.4.18.	Scroll TextBox
	16.4.19.	Use TextBox.CommandBindingst to bind command
	16.4.20.	Use Dictionary to record which textbox has been changed and not saved
	16.4.21.	Set TextBox ContextMenu to null
	16.4.22.	TextBox Selection start, end and selected text
	16.4.23.	Scrollable TextBox Column
	16.4.24.	Check Spelling Error