RichTextBox flickers while coloring words

Question

I have a RichTextBox.

lets say I want to draw every word "test" in the text. My problem is not to find the "test" in the text, My problem is when I color the word I can see the RichTextBox Selection process.

My color function:

Private Sub DrawSubPart(ByVal StartIndex As Integer, ByVal EndIndex As Integer, ByVal col As Color)
    Dim save As Integer = TextScreen.SelectionStart
    TextScreen.SelectionStart = StartIndex                 'Here I can see the selection, And I dont want to see it.
    TextScreen.SelectionLength = EndIndex - EndIndex + 1
    TextScreen.SelectionColor = col
    TextScreen.SelectionLength = 0
    TextScreen.SelectionStart = save
End Sub

I tried to catch the Selection process and it look like that:

enter image description here

And after one millisecond it looks ok:

enter image description here

So how can I stop the Selection "flickering" ?

If you're going to use this as a syntax highlighter I suggest you use ScintillaNET instead: https://scintillanet.codeplex.com/ — Visual Vincent, Mar 13 '15 at 18:33

score 1 · Accepted Answer · answered Mar 13 '15 at 17:31

Try using a custom RichTextBox control that turns off the drawing and scrolling events while you reformat the contents:

Public Class RichTextBoxEx
  Inherits RichTextBox

  <DllImport("user32.dll")> _
  Private Shared Function SendMessage(hWnd As IntPtr, wMsg As Int32, wParam As Int32, ByRef lParam As Point) As IntPtr
  End Function

  <DllImport("user32.dll")> _
  Private Shared Function SendMessage(hWnd As IntPtr, wMsg As Int32, wParam As Int32, lParam As IntPtr) As IntPtr
  End Function

  Const WM_USER As Integer = &H400
  Const WM_SETREDRAW As Integer = &HB
  Const EM_GETEVENTMASK As Integer = WM_USER + 59
  Const EM_SETEVENTMASK As Integer = WM_USER + 69
  Const EM_GETSCROLLPOS As Integer = WM_USER + 221
  Const EM_SETSCROLLPOS As Integer = WM_USER + 222

  Private _ScrollPoint As Point
  Private _Painting As Boolean = True
  Private _EventMask As IntPtr
  Private _SuspendIndex As Integer = 0
  Private _SuspendLength As Integer = 0

  Public Sub SuspendPainting()
    If _Painting Then
      _SuspendIndex = Me.SelectionStart
      _SuspendLength = Me.SelectionLength
      SendMessage(Me.Handle, EM_GETSCROLLPOS, 0, _ScrollPoint)
      SendMessage(Me.Handle, WM_SETREDRAW, 0, IntPtr.Zero)
      _EventMask = SendMessage(Me.Handle, EM_GETEVENTMASK, 0, IntPtr.Zero)
      _Painting = False
    End If
  End Sub

  Public Sub ResumePainting()
    If Not _Painting Then
      Me.Select(_SuspendIndex, _SuspendLength)
      SendMessage(Me.Handle, EM_SETSCROLLPOS, 0, _ScrollPoint)
      SendMessage(Me.Handle, EM_SETEVENTMASK, 0, _EventMask)
      SendMessage(Me.Handle, WM_SETREDRAW, 1, IntPtr.Zero)
      _Painting = True
      Me.Invalidate()
    End If
  End Sub
End Class

Then your usage would be:

RichTextBoxEx1.SuspendPainting()
Dim save As Integer = RichTextBoxEx1.SelectionStart
RichTextBoxEx1.SelectionStart = StartIndex
RichTextBoxEx1.SelectionLength = EndIndex - StartIndex + 1
RichTextBoxEx1.SelectionColor = Color.Green
RichTextBoxEx1.SelectionLength = 0
RichTextBoxEx1.SelectionStart = save
RichTextBoxEx1.ResumePainting()

RichTextBox flickers while coloring words

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