System.Windows.Forms.NumericUpDown.OnTextBoxKeyPress C# (CSharp) Method

		protected override void OnTextBoxKeyPress(object source, KeyPressEventArgs e) {
			if ((ModifierKeys & ~Keys.Shift) != Keys.None) {
				return;
			}

			NumberFormatInfo nfi = CultureInfo.CurrentCulture.NumberFormat;
			string pressedKey = e.KeyChar.ToString ();

			if ((pressedKey != nfi.NegativeSign) && (pressedKey != nfi.NumberDecimalSeparator) && 
				(pressedKey != nfi.NumberGroupSeparator)) {
				string acceptable = hexadecimal ? "\b0123456789abcdefABCDEF" : "\b0123456789";
				if (acceptable.IndexOf (e.KeyChar) == -1) {
					// FIXME: produce beep to signal that "invalid" key was pressed
					// prevent the key from reaching the text box
					e.Handled = true;
				}
			}

			base.OnTextBoxKeyPress(source, e);
		}