c# - ASP.NET 中的 Gridview 排序

Question

我有一个gridview，它的数据源来自linq to sql语句:

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();

我正在尝试实现gridview的排序功能:

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();
    }
}

但是" DataTable dataTable = (DataTable)GridView1.DataSource; "行返回 null，但数据源计数为 4。我收到此错误:

{"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'."}

如何对 gridview 进行排序并纠正错误？谢谢..

Answer 1

您不能使用网格的DataSource 属性来获取数据源。它仅在设置后和回发结束后才可用。您需要再次从数据库中获取数据。
像这样的事情:

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();
}