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:
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.
- 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:
- Div tag for Messages: This will house/show/contain the messages that are sent by the chatters. No frames here.
- TextBox: This is where chatters will be typing their messages.
- Send Button: Sends the messages when clicked.
- Div tag for Chatters: Shows the chatters logged-in to the current room.
- Log-out Button: Logs out the user from the current room.
- 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".
- 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.
-
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
-
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
-
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
-
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
-
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:
-
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)
-
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"
>
-
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.
-
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.
-
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
-
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.
-
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.
-
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.
-
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.
As always, the code and the article are provided "As Is", there is absolutely no warranties. Use at your own risk.
Code Download: Click here to download the code
Questions, comments: junnark@gmail.com
Happy Coding!!!
Date Modified: June 26, 2008