VB.Net Custome RichTextBox SetScrollPos

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I have a control that inherits form RichTextBox. I found A couple of properties that are supposed to get/set the scroll position (and they work to some degree). Here is the one to get/set the vertical scroll position:

VB

    <dllimport("user32.dll",> _
Public Shared Function GetScrollPos(ByVal hWnd As IntPtr, ByVal nBar As Integer) As Integer
End Function

<dllimport("user32.dll")> _
Private Shared Function SetScrollPos(ByVal hWnd As IntPtr, ByVal nBar As Integer, ByVal nPos As Integer, ByVal bRedraw As Boolean) As Integer
End Function

Private Const SB_VERT As Integer = &H1
Public Property VScrollPos() As Integer
    Get
        Return GetScrollPos(DirectCast(Me.Handle, IntPtr), SB_VERT)
    End Get
    Set(ByVal value As Integer)
        SetScrollPos(DirectCast(Me.Handle, IntPtr), SB_VERT, value, True)
    End Set
End Property

The problem is that they don't refresh the content of the RichTextBox. The scroll bars refresh to their correct positions, but the text and everything else don't. I have tried Googling. I have also tried several calls including .Refresh(), Application.DoEvents(), and .Invalidate(), but none of them have worked as of yet. Is there anything else I can try in order to force the whole thing to redraw?

Thanks!
Ethan

Posted 1-Dec-11 19:43pm

Matchlighter

Updated 1-Dec-11 19:48pm

Eduard Lu

v2

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[no name] 2-Dec-11 1:48am

EDIT: updated "pre" tag

Matchlighter 2-Dec-11 2:26am

Thanks for doing that. I couldn't figure out how when I first posted. It usually does it by itself when I paste it from VS.

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strogg · Accepted Answer · 2011-12-02T07:29:00

The SetScrollPos just does that. Wont update the window.
You can use the SendMessage() function to get/set scroll position. Here's the interop

VB

Private Declare Auto Function RtfScroll _
                Lib "user32.dll" Alias "SendMessage" ( _
                ByVal hWnd As IntPtr, _
                ByVal Msg As Integer, _
                ByVal wParam As IntPtr, _
                ByRef lParam As System.Drawing.Point) As Integer

Private Const WM_USER = &H400
Private Const EM_GETSCROLLPOS = WM_USER + 221
Private Const EM_SETSCROLLPOS = WM_USER + 222

Eg to set scroll position to x=0, y =100

RtfScroll(RichTextCtl.Handle, EM_SETSCROLLPOS, 0, New System.Drawing.Point(0, 100))

To get scroll position

Dim pt As New System.Drawing.Point()
RtfScroll(rt.Handle, EM_GETSCROLLPOS, 0, pt)

==============================

There's another simpler way to achieve this without using interop.

To do it,
1. Place the cursor at the appropriate position by setting the SelectionStart property's value and setting the SelectionLength to zero.
2. call the ScrollToCaret() function to scroll to the caret