* VB-CODE (1)
Tip 133: Using the SendMessage Function to Scroll Contents of Text Box =
Controls

July 1, 1995

Abstract
In Microsoft=AE Visual Basic=AE, you can programmatically scroll through =
the contents
of a Text Box control without actually waiting for your user to click =
the Scroll
Bar control. You can do this by sending one of the scrolling messages to =
the
system with the Microsoft Windows=AE application programming interface =
(API)
SendMessage function.

Scrolling Through a Text Box Control
In the example program below, the code attached to the Left command =
button scrolls
the contents of the Text Box control to the left by one character =
position. You
accomplish this by sending a WM_HSCROLL message to the Text Box control. =
When a
user clicks the horizontal scroll bar in the Text Box, this message is =
sent to the
window. In this program, however, you send the message when the user =
clicks the
command button.

To control the direction of the scrolling action, you must tell the =
Microsoft=AE
Windows=AE application programming interface (API) SendMessage function =
to send a
WM_HSCROLL message to the Text Box control with a directional argument =
in the
wParam argument. The following shows the valid settings that you can be =
specify
for the wParam argument:

SB_LEFT       Scroll to the left all the way
SB_RIGHT      Scroll to the right all the way
SB_LINELEFT   Scroll left one unit
SB_LINERIGHT  Scroll right one unit

As you can see from the list above, to scroll the contents of the Text =
Box left by
one character, you set the wParam argument to SB_LINELEFT. To scroll the =
contents
of the Text Box right by one character, you set the wParam argument to
SB_LINERIGHT.

Example Program
This program shows how you can scroll the contents of a Text Box control =
by using
the SendMessage function.

 1. Create a new project in Visual Basic. Form1 is created by default.
 2. Add the following Constant and Declare statements to the General =
Declarations
    section of Form1 (note that the Declare statement must be typed as a =
single
    line of code):

Private Declare Function SendMessage Lib "user32" Alias "SendMessageA"
   (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Integer,
   ByVal lParam As Long) As Long
Const SB_LINERIGHT =3D 1
Const SB_LINELEFT =3D 0
Const WM_HSCROLL =3D &H114

 3. Add a Text Box control to Form1. Text1 is created by default. Set =
its
    MultiLine property to True. Set its ScrollBars property to 3-Both.
 4. Add a Command Button control to Form1. Command1 is created by =
default. Set
    its Caption property to "Left".
 5. Add the following code to the Click event for Command1:

Private Sub Command1_Click()
    Dim X As Long
    X =3D SendMessage(Text1.hwnd, WM_HSCROLL, SB_LINELEFT, ByVal 0&)
End Sub

 6. Add a second Command Button control to Form1. Command2 is created by =
default.
    Set its Caption property to "Right".
 7. Add the following code to the Click event for Command2:

Private Sub Command2_Click()
    Dim X As Long
    X =3D SendMessage(Text1.hwnd, WM_HSCROLL, SB_LINERIGHT, ByVal 0&)
End Sub

Run the example program by pressing F5. Type some text into the Text Box =
control.
Click the Left command button. The text scrolls to the left by one =
character
position. Click the Right command button. The text scrolls to the right =
by one
character position.

Additional References
"Scroll Bar Messages." (Development Library, Books and Periodicals,
   Programming Windows 3.1 by Charles Petzold, PART 1 Getting Started,
   Chapter 2 Painting with Text)
"SendMessage." (Development Library, Product Documentation, SDKs,
   Windows 3.1 SDK, Programmer's Reference Volume 2: Functions)
"WM_HSCROLL." (Development Library, Product Documentation, SDKs,
   Windows 3.1 SDK, Programmer's Reference Volume 3: Messages, =
Structures, and Macros)