WPF中的DateTimePicker控件

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.ComponentModel;

namespace DateTimePickerControl
{
    public partial class DateTimePicker : UserControl INotifyPropertyChanged
    {
        public DateTimePicker（）
        {
            InitializeComponent（）;

            DatePickerObj.SelectedDate = DateTime.Now;
            this.SendPropertyChanged（“SelectedDateTimeString“）;

            _selectedHour = DateTime.Now.Hour;
            _selectedMinute = DateTime.Now.Minute;
            _selectedSecond = DateTime.Now.Second;

            _oldTextBox = _currentTextBox = TextBox_Seconds;
            _currentTextBox.Background = Brushes.Pink;
        }
        public DateTime SelectedDateTime
        {
            get
            {
                DateTime obj = DatePickerObj.SelectedDate ?? DateTime.Now;
                return obj.Add（new TimeSpan（SelectedHour - obj.Hour SelectedMinute - obj.Minute SelectedSecond - obj.Second））;
            }
        }
        public String SelectedDateTimeString
        {
            get
            {
                return SelectedDateTime.ToString（“yyyy-MM-dd HH-mm-ss“）;
            }
        }

        #region private methods
        private void TextBox_Hours_GotFocus（object sender RoutedEventArgs e）
        {
            _oldTextBox.Background = Brushes.Transparent;
            _oldTextBox = _currentTextBox = TextBox_Hours;
            _currentTextBox.Background = Brushes.Pink;
        }
        private void TextBox_Minutes_GotFocus（object sender RoutedEventArgs e）
        {
            _oldTextBox.Background = Brushes.Transparent;
            _oldTextBox = _currentTextBox = TextBox_Minutes;
            _currentTextBox.Background = Brushes.Pink;
        }
        private void TextBox_Seconds_GotFocus（object sender RoutedEventArgs e）
        {
            _oldTextBox.Background = Brushes.Transparent;
            _oldTextBox = _currentTextBox = TextBox_Seconds;
            _currentTextBox.Background = Brushes.Pink;
        }
        private void ComboBox_DropDownClosed（object sender EventArgs e）
        {
            this.SendPropertyChanged（“SelectedDateTime“）;
            this.SendPropertyChanged（“SelectedDateTimeString“）;
        }

        private void BTN_IncreaseTime_Click（object sender RoutedEventArgs e）
        {
            Int32 result;
            if （Int32.TryParse（_currentTextBox.Text out result））
            {
                result++;
                _currentTextBox.Text = result.ToString（）;
            }
        }
        private void BTN_DecrementTime_Click（object sender RoutedEventArgs e）