Question

I have a gridview and its data source comes from linq to sql statements:

var query = from user in dataContext.tbl_files
            select new { user.File_Name, user.Upload_Time, user.Uploaded_By };

GridView1.DataSource = query.ToList();
GridView1.DataBind();

I am trying to implement sorting feature of gridview :

public void GridView1_Sorting(object sender, GridViewSortEventArgs e)
{
    string previousSortExpression = (string)ViewState["SortDirection"];
    string sortExpression = e.SortExpression;
    SortDirection sortDirection = e.SortDirection;
    if (sortExpression.Equals(previousSortExpression))
    {
        sortDirection = SortDirection.Descending;
        ViewState["SortDirection"] = string.Empty;
    }
    else
        ViewState["SortDirection"] = sortExpression;

    string direction = sortDirection == SortDirection.Ascending ? "ASC" : "DESC";
    e.SortExpression = string.Format("it.{0} {1}", e.SortExpression, direction);

    DataTable dataTable = (DataTable)GridView1.DataSource; // here returns null!

    if (dataTable != null)
    {
        DataView dataView = new DataView(dataTable);
        dataView.Sort = e.SortExpression ;
        GridView1.DataSource = dataView;
        GridView1.DataBind();
    }
}

But " DataTable dataTable = (DataTable)GridView1.DataSource; " line returns null however count of datasource is 4. I got this error :

{“Unable to cast object of type ‘System.Collections.Generic.List1[<>f__AnonymousType03[System.String,System.Nullable`1[System.DateTime],System.String]]’ to type ‘System.Data.DataTable’.”}

How can I sort my gridview and correct my mistake? Thanks..

Answer 1

You can’t use the DataSource property of the grid to fetch the data source. It is only available after it is set and to the end of that postback. You’ll need the fetch the data from the database again.
Something like this:

public void GridView1_Sorting(object sender, GridViewSortEventArgs e)
{
  var users = (from user in dataContext.tbl_files
              select new { user.File_Name, user.Upload_Time, user.Uploaded_By }).ToList().AsEnumerable();

  switch(e.SortExpression)
  {
     case "File_Name":
       users = users.OrderBy(x => x.File_Name);
       break;
     case "Upload_Time":
       users = users.OrderBy(x => x.Upload_Time);
       break;
     case "Uploaded_By":
       users = users.OrderBy(x => x.Uploaded_By);
       break;
  }
  if(e.SortDirection == SortDirection.Descending)
    users = users.Reverse();

  GridView1.DataSource = users;
  GridView1.DataBind();
}