Limit a TextBox to Numeric Entry Only in VB6

I am surprised at how often I still see this question asked, and the answer almost always involves using the KeyUp, or KeyDown event and programmatically canceling the keystroke if the key pressed was not numeric. I don’t like doing it that way because

1. It takes several lines of code to accomplish
2. It has to be done for every textbox you want to limit

So if I don’t like using the Keyup / Keydown events to limit a TextBox to numeric input, how do I choose to do it. I use the Windows API. It’s something I learned early when I started programming in Visual Basic. Many things that are hard to do with VB are much easier to do with the Windows API. In this case I use the SetWindowLong function. I have a .bas module that contains all of my common routines. This particular method is implemented as a function that takes a handle to an edit control as a parameter and returns the result of the SetWindowLong function. I can call this function for any number of TextBoxes I need to.

Option Explicit

Private Const ES_NUMBER = &H2000&
Private Const GWL_STYLE = (-16)
Private Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long

'set an editbox to numeric only - return the previous
'style on success or zero on error
Public Function ForceNumeric(ByVal EditControlhWnd As Long) As Long
   Dim lngCurStyle As Long
   Dim lngReturn As Long

   lngCurStyle = GetWindowLong(EditControlhWnd, GWL_STYLE)
   If lngCurStyle <> 0 Then
      lngReturn = SetWindowLong(EditControlhWnd, GWL_STYLE, lngCurStyle Or ES_NUMBER)
   End If

   ForceNumeric = lngReturn

End Function

To use this function:

Private Sub Form_Load()
    Dim lngResult As Long

    lngResult = ForceNumeric(Text1.hwnd)

End Sub

The limit of this approach is that it doesn’t allow for decimals. It also doesn’t allow for characters such as currency, or negative (-) signs.