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, 0);

                int offset = change[0].Offset;
                if (change[0].AddedLength > 0)
                {
                    double num;
                    if (!Double.TryParse(textBox.Text, out num))
                    {
                        textBox.Text = textBox.Text.Remove(offset, change[0].AddedLength);
                        textBox.Select(offset, 0);
                    }
                }
            }
        }

        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;
            }
        }
    }