private string oldSelectedText = "" ;
private string curSelectedText = "" ;
private void richTextBox1_SelectionChanged( object sender , EventArgs e)
{
oldSelectedText = curSelectedText; //
curSelectedText = (( RichTextBox )sender) . SelectedText;
}
private void richTextBox1_TextChanged( object sender , EventArgs e)
{
Text = " + oldSelectedText;
}