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'Controls - How to Make a TextBox accept only digits using API
'Use the SetWindowLong API function to set the TextBox's extended style to
'include ES_NUMBER. Then subclass the control to monitor its messages.

Private Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal hwnd As Long, _
    ByVal nIndex As Long, ByVal dwNewLong As Long) As Long
Private Declare Function GetWindowLong Lib "user32" Alias "GetWindowLongA" (ByVal hwnd As Long, _
    ByVal nIndex As Long) As Long
 
Private Const GWL_STYLE As Long = (-16)
Private Const ES_NUMBER As Long = &H2000
 
Private Sub Form_Load()
    Dim style As Long
 
    ' Get the current style.
    style = GetWindowLong(Text1.hwnd, GWL_STYLE)
 
    ' Add ES_NUMBER to the style.
    SetWindowLong Text1.hwnd, GWL_STYLE, style Or ES_NUMBER
End Sub