Gridview SortExpression为空

Question

下面的代码显示了在对GridView进行排序时添加上升 - 下降图像，但GridView SortExpression返回NULL。

知道为什么会这样吗？

 protected void grvSample_RowCreated(object sender, GridViewRowEventArgs e)
    {
        if (e.Row.RowType == DataControlRowType.Header)
        {
            foreach (TableCell tc in e.Row.Cells)
            {
                if (tc.HasControls())
                {
                    LinkButton lnk = (LinkButton)tc.Controls[0];
                    if (lnk != null)
                    {
                        System.Web.UI.WebControls.Image img = new System.Web.UI.WebControls.Image();
                        img.ImageUrl = "~/Images/" + (grvSample.SortDirection == SortDirection.Ascending ? "asc" : "desc") + ".gif";
                        if (grvSample.SortExpression == lnk.CommandArgument)
                        {
                            // adding a space and the image to the header link
                            tc.Controls.Add(new LiteralControl(" "));
                            tc.Controls.Add(img);
                        }
                    }
                }
            }
        }
    }

Answer 1

我不认为在创建行时会设置它。单击排序列时会设置它。