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In this article I will discuss how to sort columns in grid and more. At the end it will help answer some very frequently
asked questions like following.
- How to sort DataGird in ASP.Net?
- How to sort GridView?
- How to show sort direction image in column header of GridView or DataGrid?
- How to keep track of sorting direction and sort expression while sorting GridView?
Along with getting answers to these question I will also discuss some of the issues with implementation of sorting in
GridView. And one of the very frequently brought up issue is that
SortDirection property of
GridViewSortEventArgs is always set to Ascending.
Specifying Sorting Attributes For GridView
To enable sorting for GridView set
Sorting attribute for the control to True and if you are specifying event handlers
for controls on page itself then set the event handler function for
OnSort event of the control. The following code snippet
from ASPX page shows how these attributes are set.
<sp:GridView ID="ctlGridView" runat="server" autogeneratecolumns=False
<asp:boundfield datafield="ProductID" sortexpression="ProductID" />
<asp:boundfield datafield="Name" headertext="Name" sortexpression="Name" />
<asp:boundfield datafield="ProductNumber" headertext="Product Number" sortexpression="ProductNumber" />
OnSort Event Handler
Now when grid is loaded and user clicks on column header, OnSort event gets fired and your handler will get called. Second
parameter for event handler is
GridViewSortEventArgs which has two properties that specify sort direction and
sort expression for the column which was clicked by user. These properties are
SortDirection. Unfortunately in all my attempts I have always seen value of
set to Ascending. So only piece of useful information we have is
SortExpression. You can use this
property for multiple purposes. One basic purpose is to sort the data table with this sort expression. You can append ASC or DESC to
sort expression to sort data as per user's click action. And then you can save this sort expression in ViewState to decide if
SortDirection needs to be reversed on next click on header. You can compare SortExpression from the event argument with the one
stored in ViewState. If they are different that means a new sort command needs to be executed otherwise you simply need to
Showing Image In Column To Indicate Sort Direction
Displaying an image indicator along side the column header to show sort direction gives a very
cleat indication to user about which column is sorted and in what direction. Header is nothing more than a collection of controls. To
display an indicator image you simply need to insert appropriate image at desired location. If you look at the image shown at the top of
the article, you will notice that "Name" column has been sorted in ascending order an arrow image is shown right next to column header.
Following code snippet shows the implemenation included in the sample project of this article.
protected void OnSort(object sender, GridViewSortEventArgs e)
// There seems to be a bug in GridView sorting implementation. Value of
// SortDirection is always set to "Ascending". Now we will have to play
// little trick here to switch the direction ourselves.
if (String.Empty != m_strSortExp)
if (String.Compare(e.SortExpression, m_strSortExp, true) == 0)
(m_SortDirection == SortDirection.Ascending) ? SortDirection.Descending : SortDirection.Ascending;
ViewState["_Direction_"] = m_SortDirection;
ViewState["_SortExp_"] = m_strSortExp = e.SortExpression;
protected void OnRowCreated(object sender, GridViewRowEventArgs e)
if (e.Row.RowType == DataControlRowType.Header)
if (String.Empty != m_strSortExp)
void AddSortImage(GridViewRow headerRow)
Int32 iCol = GetSortColumnIndex(m_strSortExp);
if (-1 == iCol)
// Create the sorting image based on the sort direction.
Image sortImage = new Image();
if (SortDirection.Ascending == m_SortDirection)
sortImage.ImageUrl = "~/dwn.gif";
sortImage.AlternateText = "Ascending Order";
sortImage.ImageUrl = "~/up.gif";
sortImage.AlternateText = "Descending Order";
// Add the image to the appropriate header cell.