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Build a Web Chat Application using ASP.Net 3.5, LINQ and AJAX (in VB 9.0)


Technologies Used: ASP.Net 3.5, AJAX, JavaScript, VB 9.0, LINQ-to-SQL, MS SQL Server 2000/2005

Note: As promised a week ago, here's the VB 9.0 equivalent of the article. To see my original article in C# click here.

Introduction:

A Java Programmer friend of mine once asked me if I have ever built a web chat application. I said "No". He then asked me if I were to build a really simple, monitored, bare minimum, working web chat application, how long do I think will it take (something to that effect). I said, "I don't know". A few days had passed, one lazy evening, I was surfing the web looking for ASP.Net web chat applications. It seems that I can't find one that is simple enough to implement. So I decided to just build something simple from scratch. When I say simple, that just means that: I'm am going to try to build this web chat as fast as possible, with very minimal planning or architecturing. So what you will read below are my notes after I got done building the web chat application. Here's an example of how the chatroom page looks like:

LINQ Chatroom

Requirements:

We will create a very simple web chat application using the latest ASP.Net 3.5 technologies from scratch just for fun. This chat application will contain 2 web pages, the login page and the chatroom page. Most of the tutorial will be focused on the chatroom page. Some of the things that I want to accomplish are as follows:
  • Must be accessible anywhere, and no need to download and install any components. This is why we're going to create a web chat.
  • Web chat must be "flicker-free". This is where AJAX will be very handy.
  • We want to be able to monitor chat conversations using a database. We will use MS SQL Server to store conversations and user information.
  • No use of frames. I read somewhere that frames are evil, and I kind of agree with that.
  • Use of dynamic SQL using LINQ-to-SQL instead of stored procedures for a super fast coding. Remember that we're doing this for fun.
  • No use of Application Variables. I've seen some examples on the web that uses application variables and I just don't like this idea.
The Fun Begins!

1. First, we need to build our database using MS SQL Server 2000/2005. Note that we will only create the bare minimum just to get the web chat application going. Listed below are the table names and their primary usage for our chat application.

LINQ Chatroom table structure
  • User: Contains user information. Feel free to add your own fields like address, city, and so on.
  • Message: Will hold the messages sent by the users while chatting.
  • Room: Contains information about different rooms. This means that you can have more than one room. But for the purposes of this tutorial, we will only use one room for now.
  • LoggedInUsers: Will hold users logged-in/chatting in the chatroom(s). In short, if a user enters in a room, we will save their information here, in this way, we can show the list of users chatting in a specific room.
2. Create an ASP.Net 3.5 website using Visual Studio 2008. For now, let's create this in C# 3.5.

3. Create a Login page. Our chat application will require all users to be logged in. Creation of the registration page for a new user will not be discussed in this tutorial. Although you can see that the username and password are in plain text, in the real world I recommend using hashed values instead. The login page is really simple; if you’re authenticated then you will be redirected to room 1. Again, you can customize this so that your users can pick from a number of rooms.

4. Create the Chatroom page.

First let's talk about the main structure of the GUI (graphical user interface). As shown on the the picture, we have the following:

LINQ GUI structure
  1. Div tag for Messages: This will house/show/contain the messages that are sent by the chatters. No frames here.
  2. TextBox: This is where chatters will be typing their messages.
  3. Send Button: Sends the messages when clicked.
  4. Div tag for Chatters: Shows the chatters logged-in to the current room.
  5. Log-out Button: Logs out the user from the current room.
  6. Update Panel: This is not a visible part of the GUI, but is one of the most important part of the chat application. This panel will make sure that the messages we see is "Flicker-Free".
  7. Timer Control: This is also not visible in the GUI. The function of the timer control is to refresh our page every 7 seconds.
That's it for now, we will look at these components in more detail in a little bit.

Now let's look at the flow of the web application.
  1. All chatters must be authenticated. In short, everyone who wants to chat must login. The Default.aspx is our login page, all unauthenticated users will be redirected here. This is easily configured in our web.config file. See code below: 

       50         <authentication mode="Forms">
       51             <forms name=".ASPXAUTH" loginUrl="Default.aspx"/>
       52         </authentication>
       53 
       54         <authorization>
       55             <deny users="?" />
       56         </authorization>


    Save the UserID in a Session before redirecting the user to the chat room page. For simplicity's sake, the user is then automatically redirected to "room 1" when authenticated. Note: You can redirect the user to a page where you have a list of chatrooms and have your user pick from the list before you redirect them to the chat room page, simply add rooms to the Room table, and list them in a page. 

       12     Protected Sub Login1_Authenticate(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.AuthenticateEventArgs) Handles Login1.Authenticate
       13         Dim db As LinqChatDataContext = New LinqChatDataContext
       14 
       15         Dim user = (From u In db.Users _
       16                    Where u.Username = Login1.UserName _
       17                    And u.Password = Login1.Password _
       18                    Select u).SingleOrDefault()
       19 
       20         If Not user Is Nothing Then
       21             e.Authenticated = True
       22             Session("ChatUserID") = user.UserID
       23             Session("ChatUsername") = user.Username
       24         Else
       25             e.Authenticated = False
       26         End If
       27     End Sub


  2. The user then arrives in the chat room page. The first thing we check is the roomID from the query string. Again for simplicity's sake, the code below assumes that you passed an integer value for the roomID. You should, however, make sure that the roomID is not null and can be converted to an integer. The code below also shows that the roomID value is assigned to an invisible Label Control called lblRoomID. We could have just as easily saved this value in a Session variable, but this is my preference since we don't really need to know the roomID in other pages than the one we're currently in. We need to know the roomID value throughout the page like when we're retrieving messages for this room, or when we're inserting messages for this room, or when we're retrieving users for this room, or when we're logging users out of this room, etc., you get the idea right? 

       13             ' for simplity's sake we're going to assume that a
       14             ' roomId was passed in the query string and that
       15             ' it is an integer
       16             ' note: in reality you would check if the roomId is empty
       17             ' and is an integer
       18             Dim roomId = Request("roomId").ToString()
       19             lblRoomId.Text = roomId


  3. We want to tell all chatters that this user just logged in. So we add/insert this user to the LoggedInUser table specific to this room. Then we retrieve and show all the users for this room.

    The call to insert a message: 

       23  Me.InsertMessage(ConfigurationManager.AppSettings("ChatLoggedInText") + " " + DateTime.Now.ToString())


    The insert message method: Notice in line 84 that I'm removing the less than characters "<", simply because it blows up the app and I'm in no mood to make my web app a little bit insecure by setting the ValidateRequest to false. I was in a hurry when I wrote this web chat, now I'm thinking I should have used the AJAX Control Toolkit's Filtered Text Box instead of a regular text box where you type your messages. Oh well, maybe in part 2. 

       96     Private Sub InsertMessage(ByVal text As String)
       97         Dim db As LinqChatDataContext = New LinqChatDataContext()
       98 
       99         Dim message As Message = New Message()
      100         message.RoomID = Convert.ToInt32(lblRoomId.Text)
      101         message.UserID = Convert.ToInt32(Session("ChatUserID"))
      102 
      103         If String.IsNullOrEmpty(text) Then
      104             message.Text = txtMessage.Text.Replace("<", "")
      105             message.Color = ddlColor.SelectedValue
      106         Else
      107             message.Text = text
      108             message.Color = "gray"
      109         End If
      110 
      111         message.ToUserID = Nothing            ' in the future, we will use this value for private messages
      112         message.TimeStamp = DateTime.Now
      113         db.Messages.InsertOnSubmit(message)
      114         db.SubmitChanges()
      115     End Sub


    In the web.config file: 

       24     <appSettings>
       25         <add key="ChatLoggedInText" value="Just logged in!"/>
       26     </appSettings>


    Then we add/insert a message in the Message table saying that this user just logged in. We also need to retrieve the messages and show the updated messages in the messages box. And yes, we add or retrieve data specific to this room. Rather than I keep saying "specific to this room" all the time, I would like to say that everything we do in this chat room page is specific to this room, which simply means, we need to pass in the roomID. 

      117     ''' <summary>
      118     ''' Get the last 20 messages for this room
      119     ''' </summary>
      120     Private Sub GetMessages()
      121         Dim db As LinqChatDataContext = New LinqChatDataContext()
      122 
      123         Dim messages = (From m In db.Messages _
      124                         Where m.RoomID = Convert.ToInt32(lblRoomId.Text) _
      125                         Order By m.TimeStamp Descending _
      126                         Select m).Take(20).OrderBy(Function(m As Message) m.TimeStamp)
      127 
      128
      129 
      130         If Not messages Is Nothing Then
      131             Dim sb As StringBuilder = New StringBuilder()
      132             Dim ctr As Integer = 0    ' toggle counter for alternating color
      133 
      134             For Each message In messages
      135                 ' alternate background color on messages
      136                 If ctr = 0 Then
      137                     sb.Append("<div style='padding: 10px;'>")
      138                     ctr = 1
      139                 Else
      140                     sb.Append("<div style='background-color: #EFEFEF; padding: 10px;'>")
      141                     ctr = 0
      142                 End If
      143 
      144                 If message.User.Sex.ToString().ToLower() = "m" Then
      145                     sb.Append("<img src='Images/manIcon.gif' style='vertical-align:middle' alt=''>  " + message.Text + "</div>")
      146                 Else
      147                     sb.Append("<img src='Images/womanIcon.gif' style='vertical-align:middle' alt=''>  " + message.Text + "</div>")
      148                 End If
      149             Next
      150 
      151             litMessages.Text = sb.ToString()
      152         End If
      153     End Sub


  4. We also need to retrieve all the users logged in to this room so we can list them in the users div tag. Notice that users other than yourself will be clickable, this is because in part 2, I will show you how to send a private message to another chatter. 

       46     Private Sub GetLoggedInUsers()
       47         Dim db As LinqChatDataContext = New LinqChatDataContext()
       48 
       49         ' let's check if this authenticated user exist in the
       50         ' LoggedInUser table (means user is logged-in to this room)
       51         Dim user = (From u In db.LoggedInUsers _
       52                     Where u.UserID = Convert.ToInt32(Session("ChatUserID")) _
       53                     And u.RoomID = Convert.ToInt32(lblRoomId.Text) _
       54                     Select u).SingleOrDefault()
       55 
       56         ' if user does not exist in the LoggedInUser table
       57         ' then let's add/insert the user to the table
       58         If user Is Nothing Then
       59             Dim loggedInUser As LoggedInUser = New LoggedInUser()
       60             loggedInUser.UserID = Convert.ToInt32(Session("ChatUserID"))
       61             loggedInUser.RoomID = Convert.ToInt32(lblRoomId.Text)
       62             db.LoggedInUsers.InsertOnSubmit(loggedInUser)
       63             db.SubmitChanges()
       64         End If
       65 
       66         Dim userIcon As String
       67         Dim sb As StringBuilder = New StringBuilder()
       68 
       69         ' get all logged in users to this room
       70         Dim loggedInUsers = From l In db.LoggedInUsers _
       71                             Where l.RoomID = Convert.ToInt32(lblRoomId.Text) _
       72                             Select l
       73 
       74         For Each loggedInUser In loggedInUsers
       75             ' show user icon based on sex
       76             If loggedInUser.User.Sex.ToString().ToLower() = "m" Then
       77                 userIcon = "<img src='Images/manIcon.gif' style='vertical-align:middle' alt=''>  "
       78             Else
       79                 userIcon = "<img src='Images/womanIcon.gif' style='vertical-align:middle' alt=''>  "
       80             End If
       81 
       82             If (Not loggedInUser.User.Username = Session("ChatUsername").ToString()) Then
       83                 sb.Append(userIcon + "<a href=#>" + loggedInUser.User.Username + "</a><br>")
       84             Else
       85                 sb.Append(userIcon + "<b>" + loggedInUser.User.Username + "</b><br>")
       86             End If
       87         Next
       88 
       89         ' holds the names of the users shown in the chatroom
       90         litUsers.Text = sb.ToString()
       91     End Sub


  5. So in simple terms this is what happens. You log-in, when authenticated you get redirected to the chatroom page, when you get to the chatroom page a message is shown on the screen to alert other chatters saying that you logged in.
Now that we know the flow of the web application, let's move on to the details of how certain things work. We will look at the events that happen when an event is triggered.

Sending a Message:
  1. You will notice that the TextBox control where you type your messages keeps the focus even after you hit the "Enter Key" or when you directly click the send button. This is done in two (2) places:

    In the BtnSend_Click event: 

       160   ScriptManager1.SetFocus(txtMessage.ClientID)


    And in the Timer1_OnTick event: 

       169   ScriptManager1.SetFocus(txtMessage)


  2. You will also notice that you don't have to directly click the "send button" to send a message, you can just hit the "enter key" from your keyboard and it gets the same effect as if you directly hit the send button. Code shown below.

    <form id="form1" defaultbutton="btnSend" defaultfocus="txtMessage" runat="server" >



  3. There are a few things that happen when you send a message. Here they are in order
    • The message is inserted in the Message table.
    • The messages are retrieved from the Message table.
    • Messages are then shown on the message box. Based on the sex of the chatter, a man or woman icon is shown along with messages.
    • Users are retrieved from the LoggedInUser table.
    • Users are then reconstructed and shown in the list of chatters box. You will notice that all the other users except you is shown as a link. This is because in the next installment of this tutorial we will add on to this code and make other users clickable so that you can chat privately. For now, it's just a placeholder for future code.

  4. You will also notice that the scroll bar on the div tag for the messages are always set to the bottom of the div, this is because we are calling a client-side function that sets the position of the div scroll to the bottom every single time the page re-loads.

    From the body tag:

    <body style="background-color: gainsboro;" onload="SetScrollPosition()" onunload="LogMeOut()">



    The client side function:

    function SetScrollPosition()

    {

          var div = document.getElementById('divMessages');

          div.scrollTop = 100000000000;

    }
Logging Out:

There are two (2) ways to log out. You can log out by clicking the logout button or by closing your browser.
  1. Clicking the Log-Out button: When the user clicks the log-out button, this user is then deleted from the LoggedInUser table. A message is inserted in the Message table saying that this user logged out. 

      173     Protected Sub BtnLogOut_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnLogOut.Click
      174         ' log out the user by deleting from the LoggedInUser table
      175         Dim db As LinqChatDataContext = New LinqChatDataContext()
      176 
      177         Dim loggedInUser = (From l In db.LoggedInUsers _
      178                             Where l.UserID = Convert.ToInt32(Session("ChatUserID")) _
      179                             And l.RoomID = Convert.ToInt32(lblRoomId.Text) _
      180                             Select l).SingleOrDefault()
      181 
      182         db.LoggedInUsers.DeleteOnSubmit(loggedInUser)
      183         db.SubmitChanges()
      184 
      185         ' insert a message that this user has logged out
      186         Me.InsertMessage("Just logged out! " + DateTime.Now.ToString())
      187 
      188         ' clean the session
      189         Session.RemoveAll()
      190         Session.Abandon()
      191 
      192         ' redirect the user to the login page
      193         Response.Redirect("Default.aspx")
      194     End Sub


  2. Closing the Browser: My guess is that most users will probably NOT click the Logout button, and instead, just close their browser when they leave the chatroom. The only place where we can capture this is on the client-side. And of course my favorite script on the client side is JavaScript. We can capture this using the "onunload" function, by placing this on the body tag as shown below.

    <body style="background-color: gainsboro;" onload="SetScrollPosition()" onunload="LogMeOut()">



    The client-side JavaScript that calls back a server-side method:

    function LogMeOut()

    {

          LogOutUserCallBack();

    }



    We also need to call a server-side method to delete this user from the LoggedInUser table asynchronously from the client side. Of course there are many ways to do this. I used the CallBack feature of ASP.Net. To do this, we simply need to implement the "ICallbackEventHandler" explicitly in our code behind file, as shown below. 

        8    public partial class Chatroom : System.Web.UI.Page, System.Web.UI.ICallbackEventHandler


    The ICallbackEventHandler have 2 members that you need to explictly implement. The "RaiseCallbackEvent" is the event that handles our callback from the client side to the server side code. This is where we delete the user from the LoggedInUser table as shown below. 

      200     Public Sub RaiseCallbackEvent(ByVal eventArgument As String) Implements System.Web.UI.ICallbackEventHandler.RaiseCallbackEvent
      201         _callBackStatus = "failed"
      202 
      203         ' log out the user by deleting from the LoggedInUser table
      204         Dim db As LinqChatDataContext = New LinqChatDataContext()
      205 
      206         Dim loggedInUser = (From l In db.LoggedInUsers _
      207                             Where l.UserID = Convert.ToInt32(Session("ChatUserID")) _
      208                             And l.RoomID = Convert.ToInt32(lblRoomId.Text) _
      209                             Select l).SingleOrDefault()
      210 
      211         db.LoggedInUsers.DeleteOnSubmit(loggedInUser)
      212         db.SubmitChanges()
      213 
      214         ' insert a message that this user has logged out
      215         Me.InsertMessage("Just logged out! " + DateTime.Now.ToString())
      216 
      217         _callBackStatus = "success"
      218     End Sub


    The "GetCallbackResult" is the method where you can return a string to a JavaScript (client-side) function. So from the RaiseCallbackEvent you can assign a variable some value that is returned from the GetCallbackResult method. For our purposes, we can just return "success" or "failed" value respectively. Code is shown below. 

      196     Public Function GetCallbackResult() As String Implements System.Web.UI.ICallbackEventHandler.GetCallbackResult
      197         Return _callBackStatus
      198     End Function


    The beauty of this asynchronous/call-back processing is possible because on the Page_Load part of the code, we registered the scripts for callback. 

       26             ' create a call back reference so we can log-out user when user closes the browser
       27             Dim callBackReference As String = Page.ClientScript.GetCallbackEventReference(Me, "arg", "LogOutUser", "")
       28             Dim logOutUserCallBackScript As String = "function LogOutUserCallBack(arg, context) { " & callBackReference & "; }"
       29             Me.ClientScript.RegisterClientScriptBlock(Me.GetType(), "LogOutUserCallBack", logOutUserCallBackScript, True)
Message Retrieval and Page Refresh:

Let me talk about how we retrieve the messages from the database. There are two (2) primary ways on the way we retrieve the messages from the database to show to chatters.
  1. When we send a message: Every single time you hit that send button or the enter-key, a message is inserted in the Message table. In your chat window, you will also automatically retrieve the messages from the Message table. So, for example you're chatting with someone else, and the other chatter sent a message a second ago, that message will appear on top of message you just sent, and it will look like the other user just sent you a message. If the other user constantly sends messages, to that user, it will look like he/she is getting a response back asap, and there's no dry time when chatting.

  2. Every 7 seconds on the Timer Tick Event: If for some reason you just never send messages, the back-up is the Timer Control. The timer control will automatically refresh your window every 7 seconds to show the updated chat messages. First you would think that this is just too long. Not really, because would really just retrieve messages only when you don't send any messages for 7 seconds. The cool thing about this is; the timer counter will reset to zero (0) every single time you hit the send button or the enter key. This makes the performance of your web app a little faster.

  3. Lastly, the combination of the above mentioned retrieval process will give you better performance rather than refreshing your browser every second. It will also present the users a seemless and faster message retrieval.
Last Words:

Building this Web Chat Application was indeed fun for me, and most of all fast (about 2 hours) because of the use of LINQ. As a matter of fact, it took me a lot longer, way, way longer to write this article than to actually build the chat application in Visual Studio 2008. Of course you can improve on this chat application by adding to it, the article presented here is just to give you a taste of how fun and fast you would be able to build a chat application using LINQ and AJAX. I'm planning to write a second part to this article which will show you how you can, just as easily add a way to communicate (im other chatters privately) with other chatters privately.


Code Download: Click here to download the code

As always, the code and the article are provided "As Is", there is absolutely no warranties. Use at your own risk.

Happy Coding!!!

Date Created: Thursday, June 26, 2008


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