using System;
using System.ComponentModel;
using System.Windows.Forms;

public partial class DecimalTextBox : TextBox
{
	public DecimalTextBox()
	{
		InitializeComponent();
	}

	protected override void OnTextChanged(EventArgs e)
	{
		if (IsDecimal())
			base.OnTextChanged(e);
	}

	protected override void OnKeyPress(KeyPressEventArgs e)
	{
		if (!char.IsNumber(e.KeyChar)
			&& ((Keys)e.KeyChar != Keys.Back)
			&& (e.KeyChar != ','))
			e.Handled = true;

		if (e.KeyChar == ',' && Text.IndexOf(',') > 0)
			e.Handled = true;

		base.OnKeyPress(e);
	}

	protected override void OnGotFocus(EventArgs e)
	{
		ResetValueOnFocus();
		base.OnGotFocus(e);
	}

	private void ResetValueOnFocus()
	{
		if (IsDecimal())
		{
			if (!IsDecimalZero())
				return;
		}
		Text = "";
	}

	private bool IsDecimal()
	{
		decimal result;
		return decimal.TryParse(Text, out result);
	}

	private bool IsDecimalZero()
	{
		return (decimal.Parse(Text) == 0);
	}

	private void DecimalTextBox_Validating(object sender, CancelEventArgs e)
	{
		decimal value;
		decimal.TryParse(Text, out value);

		const string NUMBER_FORMAT_2_DIGITS = "N2";
		Text = value.ToString(NUMBER_FORMAT_2_DIGITS);
	}

	public decimal Value
	{
		get
		{
			return decimal.Parse(Text);
		}
	}
}