How to sort gridview using a dropdown list

the specific example i am referring to is this site

http://www.iamextreme.net/category.php?CategoryId=1&SubCatego开发者_JS百科ryId=0&SortBy=name

notice the sort by drop down list. basically i want to sort products according to price,name,popularity??

do i have to requery the database and retreive the sorted data in gridview again, or should i already sort the items in the gridview that are already there??

I tried to this but its the wrong approach, basically i was trying to repopulate data in the page load event, which was giving error.

Now what is the correct approach.

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You could have something like this in for the DropDownList's SelectIndexChanged Event

protected void DropDownList1_SelectIndexChanged(object sender, EventArgs e)
        {
            gvSorting.Sort(DropDownList1.SelectedValue, SortDirection.Ascending);
        }

and handle GridView's Sorting event

protected void gvSorting_Sorting(object sender, GridViewSortEventArgs e)
{
    DataTable dtSortTable = gvSorting.DataSource as DataTable;
    if (dtSortTable != null)
    {
        DataView dvSortedView = new DataView(dtSortTable);
        dvSortedView.Sort = e.SortExpression + " " + getSortDirectionString(e.SortDirection);
        gvSorting.DataSource = dvSortedView;
        gvSorting.DataBind();
    }
}

private static string getSortDirectionString(SortDirection sortDireciton)
{
    string newSortDirection = String.Empty;
    if (sortDireciton == SortDirection.Ascending)
    {
        newSortDirection = "ASC";
    }
    else
    {
        newSortDirection = "DESC";
    }
    return newSortDirection;
}

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You shouldn't have to requery the database, but it might be better overall (to ensure that new stuff gets into the results while users are browsing).

I would respond to an event (in the example case it'd be SelectedValueChanged on the DropDownList) and do the sorting there. I would sort a collection, which you either keep in Session or re-query each time, then set the GridView's DataSource and re-bind.