Forms Data Controls :: ListView And GridView Not Displaying Header

Grid View I added a function and then called it in the following event.

private void ShowNoResultFound(DataTable source, GridView gv)
{
source.Rows.Add(source.NewRow());
gv.DataSource = source;
gv.DataBind();
int columnsCount = gv.Columns.Count;
gv.Rows[0].Cells.Clear();
gv.Rows[0].Cells.Add(new TableCell());
gv.Rows[0].Cells[0].ColumnSpan = columnsCount;
gv.Rows[0].Cells[0].Text = "No Data Found";
}
protected void AppList_Selected(object sender, SqlDataSourceStatusEventArgs e)
{
if (e.AffectedRows == 0 )
{
ShowNoResultFound(AppList, GridView1);
}
}

It displays the following error The type or namespace name 'DataTable' could not be found (are you missing a using directive or an assembly reference?

ListView

Added the following. It shows the message but not the header. Also tried adding ShowHeader="True". It it not allowing it.

...
<EmptyDataTemplate>
Sorry, no data to display.
</EmptyDataTemplate>
</asp:ListView>