程序退出时更正用户修改的系统时间

程序运行时运行用户更改系统时间,
但再程序退出时调用函数把系统时间改回到 在原来的系统时间基础上 经过的时间.

        [StructLayout(LayoutKind.Sequential)]
        public struct SystemTime
        ...{
            public ushort wYear;
            public ushort wMonth;
            public ushort wDayOfWeek;
            public ushort wDay;
            public ushort wHour;
            public ushort wMinute;
            public ushort wSecond;
            public ushort wMiliseconds;
        }

        [DllImport("Kernel32.dll")]
        public static extern bool SetSystemTime(ref SystemTime sysTime);
        [DllImport("Kernel32.dll")]
        public static extern void GetSystemTime(ref SystemTime sysTime);

        /**//// <summary>
        /// 设置系统时间。
        /// </summary>
        public void ReSetSystemTime()
        ...{
            SystemTime sysTime = new SystemTime();

        // public DateTime ProgramStartTime;
        // frmMain.ProgramStartTime 在 frmMain_Load 符值：ProgramStartTime = DateTime.Now;
        // public static int sysTickCount;
        // frmMain.sysTickCount 在 frmMain_Load 符值：ProgramStartTime = System.EnvironmentTickCount;                            DateTime DateTimeNow = frmMain.ProgramStartTime.AddTicks(Convert.ToUInt16(System.Environment.TickCount - frmMain.sysTickCount));
            sysTime.wYear = Convert.ToUInt16(DateTimeNow.Year);
            sysTime.wMonth = Convert.ToUInt16(DateTimeNow.Month);

        //处置北京时间
            int nBeijingHour = DateTimeNow.Hour - 8;
            if (nBeijingHour <= 0)
            ...{
                nBeijingHour += 24;
                sysTime.wDay = Convert.ToUInt16(DateTimeNow.Day - 1);
                sysTime.wDayOfWeek = Convert.ToUInt16(DateTimeNow.DayOfWeek - 1);
            }
            else
            ...{
                sysTime.wDay = Convert.ToUInt16(DateTime.Now.Day);
                sysTime.wDayOfWeek = Convert.ToUInt16(DateTime.Now.DayOfWeek); 
            }


            sysTime.wHour = Convert.ToUInt16(nBeijingHour);
            sysTime.wMinute = Convert.ToUInt16(DateTimeNow.Minute);
            sysTime.wSecond = Convert.ToUInt16(DateTimeNow.Second);
            sysTime.wMiliseconds = Convert.ToUInt16(DateTimeNow.Millisecond);

            SetSystemTime(ref sysTime);
    }