ACC2000: How to Limit Number of Characters to Size of Text Box

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What follows is a Visual Basic for Applications procedure, LimitTextToControlWidth, that you can call from the KeyPress event of a text box to limit the amount of text a user can enter.

This procedure is ideal for developers who want to use a non- proportionally spaced font to print text into a fixed location on a pre- printed form. The LimitTextToControlWidth procedure ensures that a user will not be able to type more text than can fit in the defined area on the form.

A number of factors affect the width of text. The larger the font size, the fewer the characters that you can type. The font that you select also affects the width of characters in the text. Characters in a non-proportionally spaced font, such as Arial or Times New Roman, have different widths. The letter "i" is narrower in width than the letter "X." In addition, the letter "i" in one font may have a different width in another font. For example, the "i" in Arial font is much narrower than the "i" in Courier New font.

The following steps provide both 16-bit and 32-bit versions of the procedure, followed by an example of how to apply the procedure to controls on a form.

NOTE: The following code uses the GetTextExtentPoint Windows application programming interface (API) function. You can call this API function only from the control that has focus on an Access form.

1. Create a new module and type the following in the Declarations section:

   Option Explicit
   
   Const LOGPIXELSX = 88
   Const LOGPIXELSY = 90
   Const TWIPSPERINCH = 1440
   
   Type Size
      cx As Long
      cy As Long
   End Type
   
   
   Declare Function GetDC Lib "user32" (ByVal hWnd As Long) As Long
   Declare Function GetDeviceCaps Lib "gdi32" (ByVal hDC As Long, _
      ByVal nIndex As Long) As Long
   Declare Function GetFocus Lib "user32" () As Long
   Declare Function GetTextExtentPoint Lib "gdi32" Alias _
      "GetTextExtentPointA" (ByVal hDC As Long, ByVal lpsz As String, _
      ByVal cbString As Long, lpSIZE As Size) As Long
   Declare Function ReleaseDC Lib "user32" (ByVal hWnd As Long, _
      ByVal hDC As Long) As Long
   
   					

2. Type the following procedures:

   Sub ConvertPixelsToTwips(X As Long, Y As Long)
      Dim hDC As Long, hWnd As Long, RetVal As Long
      Dim XPIXELSPERINCH As Long, YPIXELSPERINCH As Long
   
      '' Retrieve the current number of pixels per inch, which is
      '' resolution-dependent.
      hDC = GetDC(0)
      XPIXELSPERINCH = GetDeviceCaps(hDC, LOGPIXELSX)
      YPIXELSPERINCH = GetDeviceCaps(hDC, LOGPIXELSY)
      RetVal = ReleaseDC(0, hDC)
   
      '' Compute and return the measurements in twips.
      X = (X / XPIXELSPERINCH) * TWIPSPERINCH
      Y = (Y / YPIXELSPERINCH) * TWIPSPERINCH
   End Sub
   
   Sub LimitTextToControlWidth(KeyAscii As Integer)
      Dim AC As Control
      Dim Txt As String
      Dim TxtWidth As Long, SpaceWidth As Long
      Dim hWnd As Long, hDC As Long
      Dim lpSIZE As Size
      Dim RetVal As Long
   
      '' Exit if a non-printable character is typed.
      If KeyAscii < 32 Then Exit Sub
   
      '' Record active control.
      Set AC = Screen.ActiveControl
   
      '' Get the control text.
      Txt = AC.Text & ""
   
      '' Append typed character into the text.
      If KeyAscii > 32 Then
         Txt = Left(Txt, AC.SelStart)
         Txt = Txt & Chr$(KeyAscii)
         Txt = Txt & Mid(Txt, AC.SelStart + 1 + AC.SelLength)
      End If
   
      hWnd = GetFocus()
      hDC = GetDC(hWnd)
   
      '' Compute the width of the text.
      RetVal = GetTextExtentPoint(hDC, Txt, Len(Txt), lpSIZE)
      ConvertPixelsToTwips lpSIZE.cx, lpSIZE.cy
      TxtWidth = lpSIZE.cx
   
      '' Compute width of a space.
      RetVal = GetTextExtentPoint(hDC, " ", 1, lpSIZE)
      ConvertPixelsToTwips lpSIZE.cx, lpSIZE.cy
      SpaceWidth = lpSIZE.cx
   
      '' Are there trailing spaces to contend with?
      If AC.SelStart + 1 > Len(Txt) Then
         '' Add number of spaces * SpaceWidth to width of string.
         TxtWidth = TxtWidth + ((AC.SelStart + 1 - Len(Txt)) *  _
            SpaceWidth)
      End If
   
      If TxtWidth + (SpaceWidth / 2) > AC.Width Then
         Beep
         KeyAscii = 0
      End If
   
   End Sub
   
   					

How to use the LimitTextToControlWidth Procedure

1. Create a new, blank form not based on any table or query, with the following properties:

      Form: Test1
      -----------------
      Caption: TestForm
   
      Text box
      ---------------
      Name: One
      Left: 1"
      Top: .5"
      Width: 1"
      Height: 0.1667"
      FontName: Arial
      FontSize: 12
   
      Text box
      ---------------
      Name: Two
      Left: 1"
      Top: 1"
      Width: 1"
      Height: 0.1667"
      FontName: Arial
      FontSize: 8
   
      Text box
      ---------------
      Name: Three
      Left: 1"
      Top: 1.5"
      Width: 1"
      Height: 0.3743"
      FontName: Arial
      FontSize: 24
   					

2. Call the LimitTextToControlWidth procedure from the KeyPress event of each text box above, for example:

   Sub One_KeyPress(KeyAscii As Integer)
       LimitTextToControlWidth KeyAscii
   End Sub
   					

3. View the form and try typing the following text in each text box:

   This is a test of the emergency broadcast system

   Note that the result appears as follows:

      Text box     Text allowed to type
      ---------------------------------
      One          This is a test
      Two          This is a test of the
      Three        This is