Show / Hide GridView Columns in ASP.NET

using System;
using System.Collections;
using System.Collections.Generic;
using System.Configuration;
using System.Data;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Text;

public partial class ShowHideGridViewColumnsServer : System.Web.UI.Page
{
    #region Properties & Fields

    /// <summary>
    /// List of column names
    /// </summary>
    List<string> columnNames = new List<string>() { "Id", "Description", "Assigned To", "Status" };

    private List<int> hiddenColumnIndexes
    {
        get
        {
            return ViewState["hiddenColumnIndexes"] == null ? new List<int>() : (List<int>)ViewState["hiddenColumnIndexes"];
        }
        set
        {
            ViewState["hiddenColumnIndexes"] = value;
        }
    }

    #endregion

    #region Page Load

    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            _sampleData = null;

            // Populate the GridView
            this.GridView1.DataSource = _sampleData;
            this.GridView1.DataBind();

            hiddenColumnIndexes = new List<int>();
        }
    }

    #endregion

    #region Control Events

    protected void GridView1ShowHideColumns_SelectedIndexChanged(object sender, EventArgs e)
    {
        if(this.GridView1ShowHideColumns.SelectedIndex > 0)
        {
            int columnIndex = int.Parse(this.GridView1ShowHideColumns.SelectedValue);
            hiddenColumnIndexes.Remove(columnIndex);

            SetupShowHideColumns();
        }
    }

    #endregion

    #region GridView Events

    protected void GridView1_RowCommand(object sender, GridViewCommandEventArgs e)
    {
        if (e.CommandName == "hideCol")
        {
            // Add the column index to hide to the hiddenColumnIndexes list
            hiddenColumnIndexes.Add(int.Parse(e.CommandArgument.ToString()));
        }

        SetupShowHideColumns();
    }

    protected void GridView1_RowCreated(object sender, GridViewRowEventArgs e)
    {
        // For the header row add a link button to each header
        // cell which can execute a row command
        if (e.Row.RowType == DataControlRowType.Header)
        {
            // Loop through each cell of the header row
            for (int columnIndex = 0; columnIndex < e.Row.Cells.Count; columnIndex++)
            {
                LinkButton hideLink = new LinkButton();
                hideLink.CommandName = "hideCol";
                hideLink.CommandArgument = columnIndex.ToString();
                hideLink.Text = "-";
                hideLink.CssClass = "gvHideColLink";
                hideLink.Attributes.Add("title", "Hide Column");

                // Add the "Hide Column" LinkButton to the header cell
                e.Row.Cells[columnIndex].Controls.AddAt(0, hideLink);

                // If there is column header text then
                // add it back to the header cell as a label
                if (e.Row.Cells[columnIndex].Text.Length > 0)
                {
                    Label columnTextLabel = new Label();
                    columnTextLabel.Text = e.Row.Cells[columnIndex].Text;
                    e.Row.Cells[columnIndex].Controls.Add(columnTextLabel);
                }
            }
        }

        // Hide the column indexes which have been stored in hiddenColumnIndexes
        foreach(int columnIndex in hiddenColumnIndexes)
            if (columnIndex < e.Row.Cells.Count)
                e.Row.Cells[columnIndex].Visible = false;
    }

    #endregion

    #region Private Methods

    /// <summary>
    /// Setup the drop down list, adding options based on the hiddenColumnIndexes list 
    /// </summary>
    private void SetupShowHideColumns()
    {
        this.GridView1ShowHideColumns.Items.Clear();

        if (hiddenColumnIndexes.Count > 0)
        {
            this.GridView1ShowHideColumns.Visible = true;
            this.GridView1ShowHideColumns.Items.Add(new ListItem("-Show Column-", "-1"));
            
            foreach (int i in hiddenColumnIndexes)
                this.GridView1ShowHideColumns.Items.Add(new ListItem(columnNames[i], i.ToString()));
        }
        else
        {
            this.GridView1ShowHideColumns.Visible = false;
        }

        // Populate the GridView
        this.GridView1.DataSource = _sampleData;
        this.GridView1.DataBind();
    }

    #endregion

    #region Sample Data

    /// <summary>
    /// Property to manage data
    /// </summary>
    private DataTable _sampleData
    {
        get
        {
            DataTable dt = (DataTable)Session["TestData"];

            if (dt == null)
            {
                // Create a DataTable and save it to session
                dt = new DataTable();

                dt.Columns.Add(new DataColumn("Id", typeof(int)));
                dt.Columns.Add(new DataColumn("Description", typeof(string)));
                dt.Columns.Add(new DataColumn("AssignedTo", typeof(string)));
                dt.Columns.Add(new DataColumn("Status", typeof(string)));

                dt.Rows.Add(new object[] { 1, "Create a new project", "John", "Complete" });
                dt.Rows.Add(new object[] { 2, "Build a demo applcation", "Helen", "In Progress" });
                dt.Rows.Add(new object[] { 3, "Test the demo applcation", "Peter", "Pending" });
                dt.Rows.Add(new object[] { 4, "Deploy the demo applcation", "Andy", "Pending" });
                dt.Rows.Add(new object[] { 5, "Support the demo applcation", "Claire", "Pending" });

                // Add the id column as a primary key
                DataColumn[] keys = new DataColumn[1];
                keys[0] = dt.Columns["id"];
                dt.PrimaryKey = keys;

                _sampleData = dt;
            }

            return dt;
        }
        set
        {
            Session["TestData"] = value;
        }
    }

    #endregion
}