ASP.NET GridView Subclass with Dynamic Footer Totals

A frequent requirement when using an ASP.NET GridView on a web page is to have a footer with totals for numeric columns in the GridView. Here is a GridView subclass that calculates footer totals dynamically.  It requires 3 parameters:

FirstComputedColumnIndex - the for index of the first column in the data set to be computed
FirstVisbleComputedColumnIndex - for the index of the first computed column to be shown
NumberOfComputedColumns - for the number of computed columns.

Here is the class code:

namespace Eric.TotalGrid {

  public partial class GridView : System.Web.UI.WebControls.GridView

    {

        private Indexer footerTotals;

        public int FirstComputedColumnIndex { get; set; }

        public int FirstVisbleComputedColumnIndex { get; set; }

        public int NumberOfComputedColumns { get; set; }    

        protected override void OnLoad(EventArgs e)

        {

            ShowFooter = true;

            base.OnLoad(e);

        }

        protected override void OnInit(EventArgs e)

        {

            footerTotals = new Indexer(NumberOfComputedColumns);

            InitializeComponent();

            base.OnInit(e);

        }

        private void InitializeComponent()

        {

            this.RowDataBound += new GridViewRowEventHandler(this.GridView1_RowDataBound);

        }

        protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)

        {           

            DataRowView tableData = e.Row.DataItem as DataRowView;

            if (e.Row.RowType == DataControlRowType.DataRow)

            {            

                for (int i = FirstComputedColumnIndex; i < (FirstComputedColumnIndex + NumberOfComputedColumns); i++)

                {               

                    if (tableData[i] != DBNull.Value)

                    {

                        decimal result = 0;

                        if (Decimal.TryParse(tableData[i].ToString(), out result))

                        {

                            footerTotals[i - FirstComputedColumnIndex] += result;

                        }

                    }

                }

            }

            else if (e.Row.RowType == DataControlRowType.Footer)

            {

                for (int i = 0; i < NumberOfComputedColumns; i++)

                {

                    if (e.Row.Cells.Count > (i + FirstVisbleComputedColumnIndex))

                        e.Row.Cells[i + FirstVisbleComputedColumnIndex].Text = footerTotals[i].ToString();

                }

            }

        }
}

The key to this GridView is using an Indexer class that can be accessed like an array. Here is its listing:

class Indexer

        {

            private int _upperLimit;      

            private decimal[] myArray;

            public Indexer(int limit)

            {

                _upperLimit = limit;

                myArray = new decimal[_upperLimit];

            }

            public decimal this[int index]   // Indexer declaration

            {

                get

                {

                    // Check the index limits.

                    if (index < 0 || index >= _upperLimit)

                        return 0;

                    else

                        return myArray[index];

                }

                set

                {

                    if (!(index < 0 || index >= _upperLimit))

                        myArray[index] = value;

                }

            }

        }

The Indexer class can be nested within the GridView subclass.


The last example shows how to use the custom GridView on a ASP.NET web page:
First,  use the register tag:
<%@ Register Namespace="Eric.TotalGrid" TagPrefix="x" Assembly="TotalGrid" %>

Then, use it just like any other GridView:

<x:GridView runat="server" ....
FirstComputedColumnIndex="4" FirstVisbleComputedColumnIndex="3" NumberOfComputedColumns="10"  >