All Data Of Gridview Are Sort Even When I Change The Page Index Of Gridview

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C#

my code is


readonly Image _sortImage = new Image();
public string SortDireaction
{
get {
return ViewState["SortDireaction"] != null ? ViewState["SortDireaction"].ToString() : string.Empty;
}
set
{
ViewState["SortDireaction"] = value;
}
}
private string _sortDirection;
protected new void Page_Load(object sender, EventArgs e)
{
base.Page_Load(sender, e);
if (IsPostBack) return;

BindGrid();

}

protected void GridView1_PageIndexChanging(object sender, GridViewPageEventArgs e)
      {
          GridView1.PageIndex = e.NewPageIndex;
          GridView1.DataBind();
          BindGrid();
      }

      protected void BindGrid()
      {
          var fl = GetList();
          var dt = EntitySetToDataTable.ConvertEntitySetToDataTable(fl);
          GridView1.DataSource = dt;
          GridView1.DataBind();
      }

      protected void gv_Sorting(object sender, GridViewSortEventArgs e)
      {
          SetSortDirection(SortDireaction);
          var fl = GetList();
          var dt = EntitySetToDataTable.ConvertEntitySetToDataTable(fl);
          dt.DefaultView.Sort = e.SortExpression + " " + _sortDirection;
          GridView1.DataSource = dt;
          GridView1.DataBind();
          SortDireaction = _sortDirection;
          var columnIndex = 0;
          foreach (var headerCell in GridView1.HeaderRow.Cells.Cast<DataControlFieldHeaderCell>().Where(headerCell => headerCell.ContainingField.SortExpression == e.SortExpression))
          {
              columnIndex = GridView1.HeaderRow.Cells.GetCellIndex(headerCell);
          }
          GridView1.HeaderRow.Cells[columnIndex].Controls.Add(_sortImage);
      }

      protected void SetSortDirection(string sortDirection)
      {
          if (sortDirection == "ASC")
          {
              _sortDirection = "DESC";
              _sortImage.ImageUrl = "../Images/desc.png";

          }
          else
          {
              _sortDirection = "ASC";
              _sortImage.ImageUrl = "../Images/asc.png";
          }
      }

      private IEnumerable<FileList> GetList()
      {
          var filePaths = Directory.GetFiles(MainFolder + ddlMainFolder.SelectedValue + "/" + ddlSubFolder.SelectedValue);
          return (from filePath in filePaths
              let fl = new FileInfo(filePath)
              select new FileList
              {
                  FileName = Path.GetFileName(filePath), Download = filePath, FileSize = GetFileLength(fl.Length), FileSizeInBytes = fl.Length, UploadDate = string.Format("{0:g}", fl.CreationTime)
              }).ToList();
      }

only that page should be sort which i clicked
plz help me