A Simple Scroll Controller for Winforms

 

I am currently researching “flick” scrolling for Windows XP and over.  As part of this I need the ability to scroll controls in code.

To do this I have created a wrapper around the scrolling apis to assist with this.

Here’s how to use it for an autoscrolling panel:

 

Dim loScrollIt As New ScrollController(Panel1)

loScrollIt.VerticalScroll(20)

 

Here’s the code:

Imports System.Runtime.InteropServices
Public Class ScrollController

    ' Scrollbar direction
    '
    Const SBS_HORZ = 0
    Const SBS_VERT = 1

    ' Windows Messages
    '
    Const WM_VSCROLL = &H115
    Const WM_HSCROLL = &H114
    Const SB_THUMBPOSITION = 4

    Private Declare Function GetScrollPos Lib "user32.dll" ( _
        ByVal hWnd As IntPtr, _
        ByVal nBar As Integer) As Integer

    'Example: position = GetScrollPos(textbox1.handle, SBS_HORZ)
    Private Declare Function SetScrollPos Lib "user32.dll" ( _
        ByVal hWnd As IntPtr, _
        ByVal nBar As Integer, _
        ByVal nPos As Integer, _
        ByVal bRedraw As Boolean) As Integer

    'Example: SetScrollPos(hWnd, SBS_HORZ, position, True

    Private Declare Function PostMessageA Lib "user32.dll" ( _
        ByVal hwnd As IntPtr, _
        ByVal wMsg As Integer, _
        ByVal wParam As Integer, _
        ByVal lParam As Integer) As Boolean

    'Example: PostMessageA(hWnd, WM_HSCROLL, SB_THUMBPOSITION _
    '                         + &H10000 * position, Nothing)

    Private moControl As Control

    Public Sub New(ByVal controlToScroll As Control)

        moControl = controlToScroll
    End Sub
    Public Sub VerticalScroll(ByVal amount As Integer)
        Dim liHwnd As IntPtr = moControl.Handle
        Dim Position = GetScrollPos(liHwnd, SBS_VERT) + amount

        If (SetScrollPos(liHwnd, SBS_VERT, Position, True) <> -1) Then

            PostMessageA(liHwnd, WM_VSCROLL, SB_THUMBPOSITION + _
                                       &H10000 * Position, Nothing)
        End If

    End Sub

End Class