未将对象引用设置到实例

Question

public static void GridViewToExcel(GridView gv, string excelName)
    {
        HttpContext.Current.Response.ContentEncoding = System.Text.Encoding.GetEncoding("GB2312");
        HttpContext.Current.Response.AppendHeader("Content-Disposition", "attachment;filename=" + excelName + ".xls");        //关闭 ViewState
        //this.EnableViewState = false;
        System.IO.StringWriter tw = new System.IO.StringWriter();        System.Web.UI.HtmlTextWriter hw = new HtmlTextWriter(tw);
        //获取control的HTML
        gv.RenderControl(hw);
        //把HTML写回浏览器
        HttpContext.Current.Response.Write(tw.ToString());
        HttpContext.Current.Response.End();  
        tw.Close();
        hw.Close();
    }
    public override void VerifyRenderingInServerForm(Control control)
    {
        //方法重写
    }
protected void btnExcel_Click(object sender, EventArgs e)
    {
        string[] excelCustName = new string[dtgOdOrderlt.Columns.Count];
        for (int i = 0; i < dtgOdOrderlt.Columns.Count; i++)
        {
            view_ALLodOrder col = new view_ALLodOrder();
            if (!string.IsNullOrEmpty(col.CustName.ToString()))
            {
                string headText = col.CustName.ToString();
                string names = dtgOdOrderlt.Columns[i].ToString();
                names = headText;
                int charIndex = dtgOdOrderlt.Columns[i].ToString().IndexOf('/');
                if (charIndex > -1)
                {
                    excelCustName[i] = headText.Substring(0, charIndex);
                }
                else
                {
                    excelCustName[i] = headText;
                }
            }
            else
            {
                excelCustName[i] = null;
            }
        }
        GridViewToExcel(dtgOdOrderlt, "OrderLook");
    }
    报错：如下“/AlbumFoundation”应用程序中的服务器错误。
--------------------------------------------------------------------------------未将对象引用设置到对象的实例。 
说明: 执行当前 Web 请求期间，出现未处理的异常。请检查堆栈跟踪信息，以了解有关该错误以及代码中导致错误的出处的详细信息。 异常详细信息: System.NullReferenceException: 未将对象引用设置到对象的实例。源错误: 
行 878: get
行 879:         {
行 880: return base.Getstring(ColumnNames.CustName);
行 881: }
行 882: set
 源文件: d:\Projects\AlbumFoundation.root\AlbumFoundation\WebSites\AlbumFoundation\App_Code\Concrete\view_ALLodOrder.cs    行: 880 堆栈跟踪: 
[NullReferenceException: 未将对象引用设置到对象的实例。]
   MyGeneration.dOOdads.BusinessEntity.Getstring(String columnName) +72
   Watabe.Shanghai.Albumfoundation.view_ALLodOrder.get_CustName() in d:\Projects\AlbumFoundation.root\AlbumFoundation\WebSites\AlbumFoundation\App_Code\Concrete\view_ALLodOrder.cs:880
   orders_ODOrderListtest.btnExcel_Click(Object sender, EventArgs e) in d:\Projects\AlbumFoundation.root\AlbumFoundation\WebSites\AlbumFoundation\orders\ODOrderListtest.aspx.cs:448
   System.Web.UI.WebControls.Button.OnClick(EventArgs e) +111
   System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +110
   System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +10
   System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +13
   System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +36
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +1565 

Answer 1

插入断点，依次快速检视  ColumnNames，ColumnNames.CustName,以及Getstring（） ,其中必然有一个是null或者抛出了异常

Answer 2

return base.Getstring(ColumnNames.CustName);调试下这个ColumnNames对象是否为空，或者ColumnNames.CustName这个属性为空也有可能

Answer 3

ColumnNames可能是null
设置断点调试一下！！

Answer 4

if(ColumnNames!=null)
    return base.Getstring(ColumnNames.CustName);
多加个 判断把