How to Set the Formatting Rectangle of a TextBox

MORE INFORMATION

Using the SendMessage API call and the EM_SETRECT message, you can set the formatting rectangle of a text box. If you do not send the EM_SETRECT message, the formatting rectangle defaults to the size of the client area of the text box.

You can use this API call to control where the scrolling starts in a text box. The default scrolling starts when the cursor reaches the left side of the text box. This API can make that rectangle smaller than the actual text box forcing the scrolling to start before the cursor reaches the left side of the text box.

Note the following if you do not use the message until after text has been entered into the text box:

If the text box does not have a horizontal scroll bar, and the formatting rectangle is set to be larger than the text box window, lines of text exceeding the width of the text box (but smaller than the width of the formatting rectangle) are clipped instead of wrapped.

Step-by-Step Demonstration

1. Start Visual Basic, or if you are in Visual Basic, start a new project.
2. Add a text box (Text1) to your form.
3. Set the Text1 MultiLine Property to True and the ScrollBars Property to 3 (Both).
4. Add a new module (Module1.bas) to the project.
5. Add the following code to Module1.bas:

      Type recttype
         l As Integer ' left of rectangular region
         t As Integer ' top of region
         r As Integer ' right of region
         b As Integer ' bottom of region
      End Type
      ' Note the following Declare must be on one, single line:
      Declare Function SendMessage Lib "user" (ByVal hwnd%, ByVal wMsg%,
         ByVal wp%, lp As Any) As Long
   						

6. Add the following code to the Form_Load event for Form1:

      Private Sub Form_Load ()
         EM_SETRECT = &H403      ' Set EM_SETRECT variable
         Dim rect As recttype    ' dim variable as rectype
         rect.l = 0              ' Set left to upper left corner
         rect.t = 0              ' Set top to upper left corner
         rect.r = 200            ' Set right of region
         rect.b = 200            ' Set bottom of region
         x% = SendMessage(text1.hwnd, EM_SETRECT, 0, rect)
      End Sub
   						

7. Run the program.

Start typing in the text box. Scrolling will begin when you reach the edge of your region. You can change the size of your region by changing the values of the rect type.