浅谈c# WPF中的PreviewTextInput

private void This_TextInput(object sender, TextCompositionEventArgs e)
    {
      string newText = e.Text;
      int number;
      if (int.TryParse(e.Text, out number) && number > 5)
      {
        e.Handled = false;
      }
      else
      {
        e.Handled = true;//(这一行代码非常重要，决定能否显示当前输入的内容)
      }      
      
    }

private void tb_tempreture_TextChanged(object sender, TextChangedEventArgs e)
        {
            string currentText = this.tb_tempreture.Text;
            if (!string.IsNullOrEmpty(currentText))
            {
                int length = currentText.Length;
                string lastChar = currentText.Substring(length - 1);
                Regex regex = new Regex("^[0-9]*$");
                Match match = regex.Match(lastChar);
                bool isNumber = !string.IsNullOrEmpty(match.ToString());
                int ascall = (int)Convert.ToChar(lastChar);
                //如果输入的不是中文或者英文或者顿号的情况下弹出如下警告
                if (!(ascall == 045 || ascall == 043 || isNumber))
                {
                    MessageBox.Show("字符" + "'" + lastChar + "'" + "不是有效输入，" + "请输入数字，或者是输入表示温度的‘+'和‘-'!", "提示", MessageBoxButton.OK, MessageBoxImage.Information);                   
                    this.tb_tempreture.Text = currentText.Substring(0, length - 1);                   
                    this.tb_tempreture.Select(currentText.Length,0);//每次改变之后设置光标的位置为文字的最后面
                }
            }          
 
        }