Silverlight TextBox只能输入金额

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using System.Text.RegularExpressions;


namespace SilverlightApplication24
{
    public partial class MainPage : UserControl
    {
        /// <summary>
        /// 正金额如:0, 0.1, 0.12, 111, 111.1, 111.12
        /// </summary>
        private string pattern = "^(0|[1-9][0-9]*)(.[0-9]{1,2})?$";
        public MainPage()
        {
            InitializeComponent();
            TestTextBox.LostFocus += new RoutedEventHandler(TestTextBox_LostFocus);
        }
        /// <summary>
        /// 当TextBox失去焦点时触发
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        void TestTextBox_LostFocus(object sender, RoutedEventArgs e)
        {
            Match m = Regex.Match(TestTextBox.Text, pattern);
            if (!m.Success)
            {
                TestTextBox.Text = string.Empty;
                MessageBox.Show("金额输入错误！");
            }
        }
    }
}