海康威视 NET_DVR_FindNextFile 的错误

    public struct NET_DVR_FIND_DATA
    {
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = )]

        /// <summary>
        /// 文件名
        ///     char sFileName[100];
        /// </summary>
        public string sFileName;
        /// <summary>
        /// 文件的开始时间
        /// </summary>
        public NET_DVR_TIME struStartTime;
        /// <summary>
        /// 文件的结束时间
        /// </summary>
        public NET_DVR_TIME struStopTime;
        /// <summary>
        /// 文件的大小
        /// </summary>
        public uint dwFileSize;
    }

      int FindFile = HCNetSDK.NET_DVR_FindNextFile(lRealHandle, ref Net_DVR_FindData);
             if (Findhandle != -)
             {
                 //当找到录像文件时接口将返回1000，当没有查找到文件或查找结束将返回1003或者1004，返回1002表示当前正在查找
                 while (FindFile != )
                 {
                     switch (FindFile)
                     {
                         case :
                             HCNetSDK.NET_DVR_FIND_DATA FindData = new HCNetSDK.NET_DVR_FIND_DATA();
                             FindData.sFileName = Net_DVR_FindData.sFileName;
                             FindData.dwFileSize = Net_DVR_FindData.dwFileSize;
                             FindData.struStartTime = Net_DVR_FindData.struStartTime;
                             FindData.struStopTime = Net_DVR_FindData.struStopTime;
                             dgvFile.Rows.Add(new object[] { FindData.sFileName, FindData.dwFileSize, string.Format("{0}.{1}.{2} {3}:{4}:{5}", FindData.struStartTime.dwYear, FindData.struStartTime.dwMonth, FindData.struStartTime.dwDay, FindData.struStartTime.dwHour, FindData.struStartTime.dwMinute, FindData.struStartTime.dwSecond) });
                             FindFile = HCNetSDK.NET_DVR_FindNextFile(Findhandle, ref Net_DVR_FindData);
                             break;
                         case :
                             MessageBox.Show("没有找到文件！");
                             break;
                         case :
                             FindFile = HCNetSDK.NET_DVR_FindNextFile(Findhandle, ref Net_DVR_FindData);
                             break;
                         case :
                             MessageBox.Show("查找完毕！");
                             break;
                         default:
                             MessageBox.Show("查找文件时异常");
                             break;
                     }
                 }