Question

在代码编译并运行后，我在jTable的浏览器View中收到以下错误： Object reference not set to an instance of an object.我调试了代码和代码的这一行

newlist = newlist.OrderBy(item => GetPropertyValue(item, sortExpression)).ToList();

我得到了上面提到的错误。我也通过评论这行代码确认了它。

我试图通过点击表的列标题来执行sorting，但它没有这样做并且输出错误。已经好几个星期试图找出它，但它似乎似乎不起作用。任何帮助都将是一个很大的帮助，并提前感谢。

以下是您检查的完整代码：

public JsonResult TopPlayedInVenueList1(string StartDate = "", string EndDate = "", int jtStartIndex = 0, int jtPageSize = 0, string jtSorting = null)
    {
        try
        {

            if (Request.IsAuthenticated == true)
            {
                string Path = @"C:\\5Newwithdate-1k.xls";
                OleDbConnection con = new OleDbConnection(@"Provider=Microsoft.Jet.OLEDB.4.0;Data Source= '" + Path + "';Extended Properties=" + (char)34 + "Excel 8.0;IMEX=1;" + (char)34 + "");
                OleDbDataAdapter da = new OleDbDataAdapter("select * from [Sheet1$]", con);
                con.Close();
                System.Data.DataTable data = new System.Data.DataTable();
                da.Fill(data);

                List<TopPlayed> daa = new List<TopPlayed>();

                foreach (DataRow p in data.Rows)
                {
                    TopPlayed top = new TopPlayed()
                    {
                        TrackID = Convert.ToInt32(p.Field<double>("TrackID")),
                        Date = p.Field<DateTime>("DateTimes"),
                        TrackName = p.Field<string>("TrackName"),
                        ArtistName = p.Field<string>("ArtistName"),
                        Times = Convert.ToInt32(p.Field<double>("Times"))
                    };

                    daa.Add(top);
                }

                var listOrder = daa.Where(i => i.Date >= Convert.ToDateTime(StartDate) && i.Date <= Convert.ToDateTime(EndDate)).ToList();

                if (jtStartIndex + 150 > listOrder.ToList().Count)
                {
                    int val = listOrder.ToList().Count - jtStartIndex;
                    jtPageSize = val;
                }

                var newlist = listOrder.OrderByDescending(i => i.Date).ToList().GetRange(jtStartIndex, jtPageSize);

                if (string.IsNullOrEmpty(jtSorting)) { jtSorting = "Date ASC"; }

                SortDirection sortDirection = jtSorting.ToLower().Contains("desc") ? SortDirection.DESC : SortDirection.ASC;
                string sortExpression = sortDirection == SortDirection.DESC ? jtSorting.ToLower().Replace(" desc", "") : 
                    jtSorting.ToLower().Contains(" asc") ? jtSorting.ToLower().Replace(" asc", "") : jtSorting;

                if (sortDirection == SortDirection.ASC)
                {
                 newlist = newlist.OrderBy(item => GetPropertyValue(item, sortExpression)).ToList();
                }
                else
                {
                 newlist = newlist.OrderByDescending(item => GetPropertyValue(item, sortExpression)).ToList();
                }

                return Json(new { Result = "OK", Records = newlist, TotalRecordCount = listOrder.ToList().Count });
            }

编辑：GetPropertyValue方法：

public static object GetPropertyValue(object obj, string propertyName)
    {
        return obj == null ? null : obj.GetType().GetProperty(propertyName).GetValue(obj, null);
    }

Answer 1

确保您的newList包含元素且sortExpression具有适当的值。

在对表列标题进行排序时，对象引用未设置为对象的实例

1 个答案: