Extending the Windows Forms Textbox - Numeric textbox

Written: 28 October 2012

While doing a C# Windows Forms project, I needed a numeric textbox. On googling I found this. It pretty much did what I needed, but wanted to add these features-

Restrict the user to enter only one decimal point.
The negative sign could be entered only at the begining.

Here is the modified code

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace CustomeControls
{
    class NumericTextbox : TextBox
    {
        bool allowSpace = false;
        bool allowNegative = true;

        // Restricts the entry of characters to digits (including hex), the negative sign,
        // the decimal point, and editing keystrokes (backspace).
        protected override void OnKeyPress(KeyPressEventArgs e)
        {
            base.OnKeyPress(e);

            System.Globalization.NumberFormatInfo numberFormatInfo = System.Globalization.CultureInfo.CurrentCulture.NumberFormat;
            string decimalSeparator = numberFormatInfo.NumberDecimalSeparator;
            string groupSeparator = numberFormatInfo.NumberGroupSeparator;
            string negativeSign = numberFormatInfo.NegativeSign;

            string keyInput = e.KeyChar.ToString();

            if (Char.IsDigit(e.KeyChar))
            {
                // Digits are OK
            }
            else if (keyInput.Equals(decimalSeparator))
            {
                //Make sure there is only one decimal separator
                if (this.Text.IndexOf('.') != -1)
                    e.Handled = true;
            }
            else if (this.allowNegative && keyInput.Equals(negativeSign))
            {
                //The negative sign should be the first character
                if (this.SelectionStart != 0)                
                    e.Handled = true;
            }
            else if (keyInput.Equals(groupSeparator))
            {
                // Decimal separator is OK
            }
            else if (e.KeyChar == '\b')
            {
                // Backspace key is OK
            }
            //    else if ((ModifierKeys & (Keys.Control | Keys.Alt)) != 0)
            //    {
            //     // Let the edit control handle control and alt key combinations
            //    }
            else if (this.allowSpace && e.KeyChar == ' ')
            {

            }
            else
            {
                // Swallow this invalid key and beep
                e.Handled = true;
                //System.Media.SystemSounds.Beep.Play();
            }
        }

        public int IntValue
        {
            get
            {
                return Int32.Parse(this.Text);
            }
        }

        public decimal DecimalValue
        {
            get
            {
                return Decimal.Parse(this.Text);
            }
        }

        public bool AllowSpace
        {
            set
            {
                this.allowSpace = value;
            }

            get
            {
                return this.allowSpace;
            }
        }

        public bool AllowNegative
        {
            set
            {
                this.allowNegative = value;
            }

            get
            {
                return this.allowNegative;
            }
        }
    }
}