by Darryn Frost (7 Submissions)
Category: Custom Controls/Forms/Menus
Compatability: Visual Basic 3.0
Difficulty: Intermediate
Date Added: Wed 3rd February 2021
Rating: 
(3 Votes)
This code allows you to have the smooth-scrolling effect seen in better applications on your datagrids(could also apply to other scroll bars in VB)
When you grab the trackbar and move it, VB doesn't do anything until you let go. Or if you click on the trackbar itself, the grid just jumps.
This code shows you how to change these effects so that the grid(or text) will scroll smoothly as you drag or click.
Assumes
I used the "MsgBlaster" .Bas module and type library for the subclassing, they are available free on the net, and I will upload it in a seperate Listing here right after this one
API DeclarationsPublic Type SCROLLINFO
cbSize As Long
fMask As Long
nMin As Long
nMax As Long
nPage As Long
nPos As Long
nTrackPos As Long
End Type
Public Const WM_HSCROLL = &H114
Public Const WM_VSCROLL = &H115
' Scroll Bar Commands
Public Const SB_PAGEUP = 2
Public Const SB_PAGEDOWN = 3
Public Const SB_THUMBTRACK = 5
' Scroll Bar Constants
Public Const SB_HORZ = 0
Public Const SB_VERT = 1
Public Const SB_CTL = 2
Public Const SB_BOTH = 3
Public Declare Sub Sleep Lib "Kernel32" (ByVal dwMilliseconds As Long)
VBcoders
'This is for a form with a datagrid
Option Explicit
Private m_Grid_Subclassed As Boolean
Private Const msCustomMessageName As String = "MsgBlasterCustomMessage"
Private mlCustomMessageID As Long
Private rglMsgIDs() As Long
Implements IMsgTarget
Private Sub Form_Load()
'Open a recordset and bind the grid to it here
Call SubClassGrid
End Sub
Private Sub SubClassGrid()
On Error GoTo SubClass_Error
If Not m_Grid_Subclassed = True Then
'To prevent it from trying again, since that can cause problems
m_Grid_Subclassed = True
' Register our custom message to get the message id.
mlCustomMessageID = RegisterWindowMessage(msCustomMessageName)
'The windows messages we are interested in are WM_VSCROLL and WM_HSCROLL
ReDim rglMsgIDs(1 To 3) As Long
rglMsgIDs(1) = WM_VSCROLL
rglMsgIDs(2) = WM_HSCROLL
rglMsgIDs(3) = mlCustomMessageID
MsgBlaster.SubclassWindow DataGrid1.hWnd, Me, rglMsgIDs
End If
Exit Sub
SubClass_Error:
'Since this is not a critical error, just ignore it for the user
Exit Sub
End Sub
Private Function IMsgTarget_OnMsg( _
ByVal hWnd As Long, _
ByVal msg As Long, _
ByVal wParam As Long, _
ByVal lParam As Long) As Long
Dim LOBYTE As Integer
Dim HIBYTE As Integer
Dim nRes As Long
Dim fEat As Boolean
Dim intAction As Integer
Dim pVert As Boolean
On Error GoTo SubClass_Error
'If this is False, the message will be passed along the chain
'If it is True, it will not be passed on
fEat = False
intAction = 0
Select Case msg
Case WM_VSCROLL
nRes = MsgBlaster.GetHiLoByte(wParam, LOBYTE, HIBYTE)
If LOBYTE = SB_THUMBTRACK Or LOBYTE = SB_PAGEDOWN Or LOBYTE = SB_PAGEUP Then
fEat = True
intAction = 1
pVert = True
End If
Case WM_HSCROLL
nRes = MsgBlaster.GetHiLoByte(wParam, LOBYTE, HIBYTE)
If LOBYTE = SB_THUMBTRACK Then
fEat = True
intAction = 1
pVert = False
End If
Case mlCustomMessageID
'lstLog.AddItem msCustomMessageName & vbTab & "wParam=0x" & Hex$(wParam) & vbTab & "lParam=0x" & Hex$(lParam)
End Select
If fEat = False Then
IMsgTarget_OnMsg = _
MsgBlaster.CallOrigWndProc(hWnd, msg, wParam, lParam)
Exit Function
Else
IMsgTarget_OnMsg = 1& 'Non-zero means we ate it
End If
If intAction = 1 Then SetScrollType pVert, LOBYTE
Exit Function
SubClass_Error:
Exit Function
End Function
Private Sub SetScrollType(ByVal pVert As Boolean, ByVal pLoByte As Integer)
Dim hWndVert As Long
Dim hWndHorz As Long
Dim typScroll As SCROLLINFO
Dim i As Integer
'Looking for Vertical scroll bar
hWndVert = FindWindowEx(DataGrid1.hWnd, 0&, "ScrollBar", vbNullString)
'Looking for Horizontal scroll bar
hWndHorz = FindWindowEx(DataGrid1.hWnd, hWndVert, "ScrollBar", vbNullString)
If pVert = True Then
If Not hWndVert = 0 Then
typScroll.cbSize = LenB(typScroll)
typScroll.fMask = 31
If GetScrollInfo(hWndVert, SB_CTL, typScroll) <> 0 Then
Select Case pLoByte
Case SB_THUMBTRACK
DataGrid1.Scroll 0, typScroll.nTrackPos - typScroll.nPos
Case SB_PAGEDOWN
For i = 1 To DataGrid1.VisibleRows - 1
DataGrid1.Scroll 0, 1
Sleep 25
Next i
Case SB_PAGEUP
For i = 1 To DataGrid1.VisibleRows - 1
DataGrid1.Scroll 0, -1
Sleep 25
Next i
End Select
End If
End If
Else
If Not hWndHorz = 0 Then
typScroll.cbSize = LenB(typScroll)
typScroll.fMask = 31
If GetScrollInfo(hWndHorz, SB_CTL, typScroll) <> 0 Then
DataGrid1.Scroll typScroll.nTrackPos - typScroll.nPos, 0
End If
End If
End If
End Sub