this could also be your Solution - integrate the functionality into your own customized Textbox :
Public Class NumericTextbox
Inherits TextBox
Private Sub NumericTextBox\_KeyPress(sender As Object, e As KeyPressEventArgs) Handles Me.KeyPress
Dim keyChar = e.KeyChar
If Char.IsControl(keyChar) Then
'Allow all control characters.
ElseIf Char.IsDigit(keyChar) OrElse keyChar = "."c Then
Dim box As TextBox = DirectCast(sender, TextBox)
Dim text As String = box.Text
Dim selectionStart As Integer = box.SelectionStart
Dim selectionLength As Integer = box.SelectionLength
text = text.Substring(0, selectionStart) & keyChar & text.Substring(selectionStart + selectionLength)
Dim valueInt32 As Integer
Dim valueDouble As Double
If Integer.TryParse(text, valueInt32) AndAlso valueInt32 > 999 Then
' Reject an integer that is longer than 3 digits.
e.Handled = True
ElseIf Double.TryParse(text, valueDouble) AndAlso text.IndexOf("."c) < text.Length - 4 Then
' Reject a real number with two many decimal places.
e.Handled = True
End If
Else
' Reject all other characters.
e.Handled = True
End If
End Sub
End Class
