Public Class RichTextBoxEx
   Inherits System.Windows.Forms.RichTextBox
 
   Private pSearchIndex As Integer
   Public Property SearchIndex() As Integer
      Get
         Return pSearchIndex
      End Get
      Set(ByVal value As Integer)
         pSearchIndex = value
      End Set
   End Property
 
   Public Function SearchString(ByVal Search As String, ByVal SearchOptions As _
     Windows.Forms.RichTextBoxFinds) As Boolean
      Dim i As Integer
 
      Try
         If (SearchOptions And Windows.Forms.RichTextBoxFinds.Reverse) = _
           Windows.Forms.RichTextBoxFinds.Reverse Then
            i = Me.Find(Search, 0, Me.SearchIndex, SearchOptions)
         Else
            i = Me.Find(Search, Me.SearchIndex, SearchOptions)
         End If
      Catch ex As Exception
 
      End Try
 
      Me.Focus()
 
      If i < 0 Then
         Return False
      Else
         Me.SearchIndex = i + 1
         Return True
      End If
   End Function
 
   Public Sub MarkString(ByVal text As String, ByVal color As Color, ByVal _
     SearchOptions As Windows.Forms.RichTextBoxFinds)
      Do Until SearchString(text, SearchOptions) = False
         If Me.SelectedText.Length > 0 Then
            Me.SelectionColor = color
         End If
      Loop
      SearchIndex = 0
   End Sub
 
   Private Sub Editor_SelectionChanged(ByVal sender As System.Object, ByVal e _
     As System.EventArgs) Handles MyBase.SelectionChanged
      SearchIndex = Me.SelectionStart
   End Sub
End Class

Public Class Form1
   Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
     System.EventArgs) Handles Button1.Click
      RichTextBoxEx1.MarkString(TextBox1.Text, Color.Red, _
      RichTextBoxFinds.MatchCase)
 
      RichTextBoxEx1.SelectionStart = 0
      RichTextBoxEx1.SelectionLength = 0
   End Sub
 
   Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As _
     System.EventArgs) Handles Button2.Click
      RichTextBoxEx1.MarkString(TextBox2.Text, Color.Green, _
      RichTextBoxFinds.MatchCase)
 
      RichTextBoxEx1.SelectionStart = 0
      RichTextBoxEx1.SelectionLength = 0
   End Sub
End Class