限制TextBox输入，只能输入Double类型数字

      public class TextBoxDouble : TextBox
     {
         public TextBoxDouble()
         {
             KeyDown += TextBoxDouble_KeyDown;
             TextChanged += TextBoxDouble_TextChanged;
         }

         private void TextBoxDouble_TextChanged(object sender, TextChangedEventArgs e)
         {
             //屏蔽非法字符粘贴
             var textBox = sender as TextBox;
             if (textBox != null)
             {
                 var change = new TextChange[e.Changes.Count];
                 e.Changes.CopyTo(change, );

                 int offset = change[].Offset;
                 if (change[].AddedLength > )
                 {
                     double num;
                     if (!Double.TryParse(textBox.Text, out num))
                     {
                         textBox.Text = textBox.Text.Remove(offset, change[].AddedLength);
                         textBox.Select(offset, );
                     }
                 }
             }
         }

         private void TextBoxDouble_KeyDown(object sender, KeyEventArgs e)
         {
             var txt = sender as TextBox;
             if ((e.Key >= Key.NumPad0 && e.Key <= Key.NumPad9) || e.Key == Key.Decimal)
             {
                 // 允许输入小键盘数字0-9或者点号
                 if (txt != null && (txt.Text.Contains(".") && e.Key == Key.Decimal))
                 {
                     // 不允许输入多个点号
                     e.Handled = true;
                     return;
                 }
                 e.Handled = false;
             }
             else if (((e.Key >= Key.D0 && e.Key <= Key.D9) || e.Key == Key.OemPeriod) &&
                      e.KeyboardDevice.Modifiers != ModifierKeys.Shift)
             {
                 // 允许输入数字0-9或者点号 并且不能按着Shift
                 if (txt != null && (txt.Text.Contains(".") && e.Key == Key.OemPeriod))
                 {
                     // 不允许输入多个点号
                     e.Handled = true;
                     return;
                 }
                 e.Handled = false;
             }
             else if (e.Key == Key.Enter)
             {
                 // 允许输入回车
                 e.Handled = false;
             }
             else
             {
                 e.Handled = true;
             }
         }
     }