Mark the text control as being changed to prevent any text content or selection changed events

    


<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

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

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