Private Sub TextBox_KeyPress_char(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyPressEventArgs)
End Sub
Private Sub TextBox_KeyPress_char(ByVal sender As System.Object, ByVal e As System.Windows.Forms.KeyPressEventArgs)
        If e.KeyChar = "." Then
            e.KeyChar = ","
        End If
        If CType(sender, TextBox).Text = String.Empty And e.KeyChar = ","Then
            e.Handled = True
            Return
        End If
        '---if textbox already has a decimal point---
        If CType(sender, TextBox).Text.Contains(DECIMAL_POINT) And e.KeyChar = "," Then
            e.Handled = True
            Return
        End If
        '---if the key pressed is not a valid decimal number---
        If (Not (Char.IsDigit(e.KeyChar) Or Char.IsControl(e.KeyChar) Or (e.KeyChar = ","))) Then
            e.Handled = True
        End If
End Sub