Chris Newman - Generics

Sunday, March 09, 2008

ASP.NET Persistent Checkbox State in a GridView With Data Paging.

One major downsides of using a checkbox in a GridView control to handle mass updates and deletes is that the state of the checkboxs will be lost when going to another page.

To work around this were going to have to write some code to save and load the state of the checkboxes.

You can download the files below.

gridviewCheckbox.zip

The 1st thing we want to do is set up our GridView and a DataSource.

         <%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>

        <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

        <html xmlns="http://www.w3.org/1999/xhtml">

        <head runat="server">

            <title>Grid View Check Box Example</title>

        </head>

        <body>

            <form id="form1" runat="server">

                <div>

                    <asp:GridView ID="Gridview1" OnDataBound="Gridview1_OnDataBound" runat="server" Width="100%" OnPageIndexChanging="Gridview1_PageIndexChanging" AllowPaging="True" AutoGenerateColumns="False" DataKeyNames="recordID" DataSourceID="AccessDataSource1">

                        <Columns>

                            <asp:BoundField DataField="recordID" HeaderText="recordID" InsertVisible="False" ReadOnly="True" SortExpression="recordID" />

                            <asp:TemplateField>

                                <ItemTemplate>

                                    <asp:CheckBox ID="chkPerson" runat="server" />

                                </ItemTemplate>

                            </asp:TemplateField>

                            <asp:BoundField DataField="firstName" HeaderText="firstName" SortExpression="firstName" />

                            <asp:BoundField DataField="lastName" HeaderText="lastName" SortExpression="lastName" />

                        </Columns>

                        <HeaderStyle HorizontalAlign="Left" />

                    </asp:GridView>

                    <asp:AccessDataSource ID="AccessDataSource1" runat="server" DataFile="~/App_Data/gridviewCheckbox.mdb" SelectCommand="SELECT [recordID], [firstName], [lastName] FROM [record]"></asp:AccessDataSource>

                    <br />

                    <br />

                    <asp:Button ID="bttnMassUpdate" runat="server" OnClick="bttnMassUpdate_Click" Text="Mass Update" /><br />

                </div>

            </form>

        </body>

        </html>

For those of you who are unfamiliar with grid views, The DataKeyNames property is set to the PrimaryKey column of your datasource and in this example its the recordID column.

The OnDataBound and OnPageIndexChanging properties are set to the name of the functions I created that I want called when these events are fired.

I used a AccessDataSource for this example because It would allow anyone to download and run this example without the need to install a SQL server.

The data in this Access Database was generated with http://www.generatedata.com/.

Now since we have our aspx page setup we need to choose a data structure that can hold the primary key for each select row. I chose a List for this task.

protected void Page_Load(object sender, EventArgs e)

       if (!Page.IsPostBack)

           List<int> list = new List<int>();

           Session["gridSave"] = list;

Now when we go to another page we need a way to store the primary key of each row that has been selected and to also remove any key that has been unselected.

private void saveValues()

    List<int> list = (List<int>)Session["gridSave"];

    foreach (GridViewRow row in Gridview1.Rows)

        int id = (int)Gridview1.DataKeys[row.RowIndex].Value;

        bool chk = ((CheckBox)row.FindControl("chkPerson")).Checked;

        if (chk)

            //see if we have a id added already

            if (list.Contains(id) == false)

                list.Add(id);

        else

            if (list.Contains(id))

                list.Remove(id);

    Session["gridSave"] = list;

Everytime we go to a new page we will also have to see if any checkboxes need to be checked

private void loadValues()

    List<int> list = (List<int>)Session["gridSave"];

    foreach (GridViewRow row in Gridview1.Rows)

        int id = (int)Gridview1.DataKeys[row.RowIndex].Value;

        if (list.Contains(id))

            CheckBox chkPerson = (CheckBox)row.FindControl("chkPerson");

            chkPerson.Checked = true;

The above functions are called from the GridViews PageIndexChanging and OnDataBound Events.

protected void Gridview1_PageIndexChanging(object sender, GridViewPageEventArgs e)

       saveValues();

       Gridview1.PageIndex = e.NewPageIndex;

   protected void Gridview1_OnDataBound(object sender, EventArgs e)

       loadValues();

Sunday, March 09, 2008 1:48:42 AM (Eastern Standard Time, UTC-05:00)

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Tuesday, January 08, 2008

Dictionary VS Hash Table

Posted in ASP.NET | Generics

We all know how useful a hash table can be, but if you are using the .NET Framework 2.0 you should be using a Dictionary instead. A dictionary and a hash table in .NET 2.0 are very similar but with 1 main difference, a dictionary is faster because it does not need to box and unbox the data as a hash table would.

I made a simple program to see just how much faster a dictionary is than a hash table. I ran the test 20 times for each data set and the results were close each time. A GUID as the key and a boolean as the data.

This is the results of the last test for each dataset.

Time in Milliseconds for 100,000 keys	Dictionary	Hash Table
Inserting	34.41264	76.0970
Reading	18.9005	31.1648
Deleting	21.2474	30.4655

Time in Seconds for 10,000,000 keys	Dictionary	Hash Table
Inserting	6.5704143	26.9096540
Reading	3.1362891	5.6670613
Deleting	3.4623316	4.8830676

My comp specs

Vista Business 32bit, AMD 64 x2 5000+, 2GB ram

and now for the code I used. You can also download the project.

hashVsDictionary.zip

using System;

using System.Collections;

using System.Collections.Generic;

using System.Diagnostics;

namespace hashVsDictionary

    internal class Program

        private static void Main(string[] args)

            #region init

            int num = 10000000;

            Guid[] guids = new Guid[num];

            Stopwatch s = new Stopwatch();

            s.Start();

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

                guids[i] = Guid.NewGuid();

            s.Stop();

            Console.WriteLine("Data Creation = " + s.Elapsed);

            s.Reset();

            #endregion

            #region hash

            Hashtable hash = new Hashtable();

            s.Start();

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

                hash.Add(guids[i], true);

            s.Stop();

            Console.WriteLine("Insert Hash = " + s.Elapsed);

            s.Reset();

            s.Start();

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

                bool b = Convert.ToBoolean(hash[guids[i]]);

            Console.WriteLine("Extracting Hash = " + s.Elapsed);

            s.Reset();

            s.Start();

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

                hash.Remove(guids[i]);

            Console.WriteLine("Removing Hash = " + s.Elapsed);

            s.Reset();

            #endregion

            #region dict

            Dictionary<Guid, bool> dict = new Dictionary<Guid, bool>();

            s.Start();

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

                dict.Add(guids[i], true);

            s.Stop();

            Console.WriteLine("Insert Dictionary = " + s.Elapsed);

            s.Reset();

            s.Start();

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

                bool b = dict[guids[i]];

            Console.WriteLine("Extracting Dict = " + s.Elapsed);

            s.Reset();

            s.Start();

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

                dict.Remove(guids[i]);

            Console.WriteLine("Removing Dict = " + s.Elapsed);

            s.Reset();

            #endregion

            Console.ReadLine();

Tuesday, January 08, 2008 2:18:33 AM (Eastern Standard Time, UTC-05:00)

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