Q161270: HOWTO: Extend the Scrolling Capabilities of a TextBox Control

Article: Q161270
Product(s): Microsoft Visual Basic for Windows
Version(s): 
Operating System(s): 
Keyword(s): kbVBp500 kbVBp600 kbGrpDSVB
Last Modified: 11-JAN-2001

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The information in this article applies to:

- Microsoft Visual Basic Control Creation Edition for Windows, versions 5.0, 6.0 
- Microsoft Visual Basic Learning Edition for Windows, versions 5.0, 6.0 
- Microsoft Visual Basic Professional Edition for Windows, versions 5.0, 6.0 
- Microsoft Visual Basic Enterprise Edition for Windows, versions 5.0, 6.0 
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SUMMARY
=======

Using the Windows API function SendMessage, you can scroll text a specified
number of lines vertically and/or a specified number of columns horizontally in
a text box. You can also scroll text programmatically, without any user
interaction. This technique extends a text box's scrolling capabilities beyond
those provided by its built-in properties and methods.

MORE INFORMATION
================

In Visual Basic, you can scroll text in a text box vertically or horizontally by
actively clicking the vertical or horizontal scroll bar respectively, at run
time. However, the text always scrolls one line or one column per click of the
scroll bar. Furthermore, there are no built-in properties or methods to scroll
text without user interaction. To work around these limitations, you can call
the Windows API SendMessage function using the EM_LINESCROLL message.
SendMessage requires the following parameters:

     SendMessage(hWnd, EM_LINESCROLL, wParam, lParam) where:

- hWnd is the hWnd of the text box.

- wParam is used to specify the number of horizontal columns to scroll. A
  positive value causes text to scroll to the left. A negative value causes
  text to scroll to the right.

- lParam is used to specify the number of vertical lines to scroll. A positive
  value causes text to scroll upward. A negative value causes text to scroll
  downward.

SendMessage returns True if the text box is multiline and False if it is
single-line. Note that calling SendMessage to scroll text vertically does not
require a vertical scroll bar, but the length of text within the text box should
exceed the text box height. To scroll text horizontally, a scroll bar is
required.

Step-by-Step Example
--------------------

1. Start a new Standard EXE project. Form1 is added by default.

2. Add a TextBox control, Text1, to Form1 and change its MultiLine property to
  True and its ScrollBars property to 3-Both.

3. Add two CommandButton controls, Command1 and Command2, to Form1.

4. Add the following code to the General Declarations section of Form1:

        Const EM_LINESCROLL = &HB6

        Private Declare Function SendMessage Lib "User32" Alias _
        "SendMessageA" _
           (ByVal hWnd As Long, _
            ByVal wMsg As Integer, _
            ByVal wParam As Integer, _
            ByVal lParam As Long) As Long

        Private Sub Form_Load()
           Dim intLineIndex As Integer, intWordIndex As Integer

           'Initialize Text1.
           Text1.Font = "Courier New"
           Text1.Text = ""
           For intLineIndex = 1 To 25             'Add 25 lines of text.
              Text1.Text = Text1.Text & "Line" & Str$(intLineIndex)
              For intWordIndex = 1 To 5           'Make each line 12 words
                                                  'long.
                 Text1.Text = Text1.Text & " Word" & Str$(intWordIndex)
              Next intWordIndex
              Text1.Text = Text1.Text & vbCrLf
           Next intLineIndex

           Command1.Caption = "Vertical"
           Command2.Caption = "Horizontal"
        End Sub

        Private Sub Command1_Click()
           Dim lngRet As Long

           lngRet = SendMessage(Text1.hWnd, EM_LINESCROLL, 0, 5&)
        End Sub

        Private Sub Command2_Click()
           Dim lngRet As Long

           lngRet = SendMessage(Text1.hWnd, EM_LINESCROLL, 5, 0&)
        End Sub

5. Press the F5 key to run the program. Click "Vertical" to scroll the text up
  five lines at a time and click "Horizontal" to scroll the text left five
  columns at a time.

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Keywords          : kbVBp500 kbVBp600 kbGrpDSVB 
Technology        : kbVBSearch kbAudDeveloper kbZNotKeyword6 kbZNotKeyword2 kbVB500Search kbVB600Search kbVBA500Search kbVBA500 kbVBA600 kbVB500 kbVB600 kbZNotKeyword3
Issue type        : kbhowto

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