为什么 GridView 的 SortExpression 在 RowDataBound 上变空 - C#

Question

我想在排序网格视图的 header 上显示 up/down 箭头。我已经在下面附加的代码中实现了它，但是在行数据绑定事件中，sortexpression 是空的。因此，我无法设置图像的排序方向。

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False"
CssClass="gridview_alter"  GridLines="Both"  
Caption="Submissions today"  CaptionAlign="Top"          
AllowSorting="true"
AllowPaging="true"  PageSize="10" OnPageIndexChanging="GridView1_PageIndexChanging" 
OnRowCommand="GridView1_RowCommand" OnRowDataBound="GridView1_RowDataBound" 
OnSorting="GridView1_Sorting">

<Columns>
<asp:BoundField DataField="student_name" HeaderText="student_name" 
ReadOnly="True"  SortExpression="student_name">  </asp:BoundField>                             
<asp:BoundField DataField="Role" HeaderText="Role" 
ReadOnly="True"  SortExpression="Role">  </asp:BoundField>                  
</Columns> 

</asp:GridView>

protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{
  string imgAsc = @" <img src='~/images/up.png' border='1' title='Ascending' 'width='50' height='50' />";
  string imgDes = @" <img src='~/images/dwn.png' border='1' title='Descendng' 'width='50' height='50' />";
 if (e.Row.RowType == DataControlRowType.Header)
 {
        foreach (TableCell td in e.Row.Cells)
        {
         LinkButton lnkbtn = (LinkButton)td.Controls[0];

        if (lnkbtn.Text == GridView1.SortExpression)//sortexpression is grtting empty here
            {
                if (GridView1.SortDirection == SortDirection.Ascending)
                {
                    lnkbtn.Text += imgAsc;
                }
                else
                    lnkbtn.Text += imgDes;
            }
        }
    }

Answer 1

检查 sortexpression（以及任何基于排序的工作）的最佳位置是 Gridview 的 OnSorting 事件。

因此，在此 OnSorting 事件中，您可以获得 Header 行并应用 ASC / DESC 图像。

protected void GridView1_Sorting(object sender, GridViewSortEventArgs e)
  {
    // Get the header row.
    GridViewRow headerRow = GridView1.HeaderRow;
    if(headerRow != null)
     {
        foreach (TableCell td in headerRow.Cells)
         {
            LinkButton lnkbtn = (LinkButton)td.Controls[0];

             if (lnkbtn.Text == e.SortExpression)
               {
                  if (GridView1.SortDirection == SortDirection.Ascending)
                  {
                      lnkbtn.Text += imgAsc;
                  }
                  else
                    lnkbtn.Text += imgDes;
               }
         }        
     }
  }

为什么 GridView 的 SortExpression 在 RowDataBound 上变空 - C#

Why is SortExpression of GridView getting empty on RowDataBound - C#

c#

asp.net

gridview

sortexpression