VB Forum / General 2 / September 2004

One way would be to use a ListBox to hold the data items.  If you have
no interest in anything except the last N items, here's one way to do
that (air code).

Start with the listbox sized to show the number of lines you care to see
at once.  N/2 lines might be a convenient number, or maybe all N --
whatever you like.

Option Explicit

Private Sub Command1_Click

Const nLines As Long = 20

Dim hFile As Long
Dim Buff As String

List1.Clear
hFile = FreeFile
Open Text1.Text For Input As hFile
Do Until EOF(hFile)
  Line Input #hFile, Buff
  With List1
     If .ListCount > nLines Then
        .RemoveItem 0
     End If
     .AddItem Left$(Buff, 60)
     .TopIndex = .ListCount - 1  'latest at the bottom
     .Refresh
  End With
  Sleep 100    ' gives time to read screen
Loop
Close #hFile

End SUb

Maybe choose the Sleep value with a slider -- if so, add a DoEvents so
the form will be responsive.

Another way is to add a timer to your Form and let it read the chunks
of 20 records, adding it to (or replacing the contents of) a multiline
Textbox.

In fact, there is even an easier solution. The RichTextBox should be
able to handle a 20 meg file without problems. So just read the file
with the RichTextbox's loadfile function. Then have a timer fire off
an EM_LINESCROLL message to the box at a suitable period.

Add a RichTextBox to your Form and paste this code in.
You may want to add a pause/start button too, so you can pause and
restart at will, by dis- or en-abling the timer.

Option Explicit

Private Const EM_LINESCROLL = &HB6
Private Declare Function SendMessage Lib "user32" Alias _
"SendMessageA"  (ByVal hwnd As Long, ByVal wMsg As Long, _
ByVal wParam As Long, lParam As Any) As Long

Private Sub Form_Load()
   Timer1.Enabled = False
    Timer1.Interval = 2000
   RichTextBox1.LoadFile "insert your file's path here"
   Timer1.Enabled = True
End Sub

Private Sub Timer1_Timer()
   'scroll 1 line at a time.
    ' Return value from SendMsg is the number of lines scrolled
   If SendMessage(RichTextBox1.hwnd, EM_LINESCROLL, 0, _
    ByVal 1) = 0 Then
       'we're done, so disable the timer.
       Timer1.Enabled = False
   End If
End Sub