GridView Sort Column Arrow Performance

I see code like the following a lot:

protected void GridView1_RowCreated(object sender, GridViewRowEventArgs e)
{
     if (e.Row.RowType == DataControlRowType.Header)
            if (String.Empty != this.GridView1.SortExpression)  
                     AddSortImage(e.Row);             
           
}

The problem with this is that it fires for each row in the GridView slowing performance.  A better way is the following which only fires once per GridView binding:

The supporting methods are:

void AddSortImage(GridViewRow headerRow) 
{ 
     int iCol = GetSortColumnIndex();
     if (-1 == iCol) 
           return; 

     // Create the sorting image based on the sort direction.

     Image sortImage = new Image();
     if (SortDirection.Ascending == this.GridView1.SortDirection) 

}
      // Add the image to the appropriate header cell.
        headerRow.Cells[iCol].Controls.Add(new LiteralControl(" "));
        headerRow.Cells[iCol].Controls.Add(sortImage);
}

public int GetSortColumnIndex()
{
      // Iterate through the Columns collection to determine the index
      // of the column being sorted. 
      foreach (DataControlField field in GridView1.Columns)
       {
             if (field.SortExpression == this.GridView1.SortExpression)
               {
                  return this.GridView1.Columns.IndexOf(field);
                }
         }
      return -1;
}