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        protected override void OnTextBoxKeyPress(object source, System.Windows.Forms.KeyPressEventArgs e)                    
        {
            base.OnTextBoxKeyPress(source, e);
            if (e.Handled)
                return;

            string decimalSeparator = CultureInfo.CurrentCulture.NumberFormat.NumberDecimalSeparator;

            if (!char.IsNumber(e.KeyChar) && !e.KeyChar.ToString().Equals(decimalSeparator))
            {
                e.Handled = char.IsLetter(e.KeyChar) || char.IsPunctuation(e.KeyChar);
                return;
            }

            TextBox innerTextBox = source as TextBox;
        
            string previewString = innerTextBox.Text.Insert(innerTextBox.SelectionStart, e.KeyChar.ToString());
            double previewValue;

            if (double.TryParse(previewString, out previewValue))
            {
                int index = previewString.IndexOf(decimalSeparator);                
                if (index == -1)
                {
                    e.Handled = false; 
                }
                else
                {
                    int decPlaces = previewString.Length - (index + decimalSeparator.Length);
                    e.Handled = decPlaces > this.DecimalPlaces; 
                }
            }
            else
               e.Handled = true;
        }