Introduction
Users are always
interested in a rich experience, or a well UI Experience. They expect real-time
action between both client and server, no matter if the technology used is
HTML5 web sockets or something else. There comes the SignalR. It is framework
built on top of ASP.NET and JavaScript library that helps to build rich
interactive web applications.
We can use signalR in the scenarios where require polling server
after fix interval to check if server has something which client needs to
update. Well, In Definition “SignalR is an asynchronous signaling framework that helps maintain persistent
connections between client and server”. It uses the raw technique of
keeping connections open between a web client and a web server. Actually it
uses an existing technique called long polling. Behind the scenes, it could
very well use Web Sockets transparently.
How it works
Long Polling: With long-polling, the browser sends a
request to the server and the server keeps the request open for a set period. If a notification is received within that
period, a response containing the message is sent to the client. If a
notification is not received within the set time period, the server sends a
response to terminate the open request
SignalR: SignalR registers some code to run at
application start time that finds all hubs in your application which is done by
jquery.signalR.min.js and SignalR.dll. On the first request to signalr/hubs,
the proxy is generated and cached for the lifetime of the application.
Server Hub:
[HubName("testHub")]
[HubName("testHub")]
public class TestingHub :Hub
{
/// <summary>
/// This method is called from signalR client
/// Clients is dynamic property.
/// </summary>
/// <param
name="message"></param>
public void Send(string
message)
{
Clients.broadcastMessage(message);
}
}
Client Side Scripting:
<script src="Scripts/jquery-1.4.1.min.js" type="text/javascript"></script>
<script src="Scripts/jquery.signalR.min.js" type="text/javascript"></script>
<script src="/signalr/hubs" type="text/javascript"></script>
<script type="text/javascript">
$(function () {
var broadCaster = $.connection.testHub;
broadCaster.broadcastMessage = function (message) {
$('#brodcastArea').html(message);
};
$.connection.hub.start();
$('#btnBroadCast').click(function () {
broadCaster.send($('#txtMessage').val());
});
});
</script>
Business problem
with SignalR
Real time stock
update system, we can create a very interactive stock updating tool, which
reflects the live stock market change to the clients. Our server will communicate to Stock API’s and
updates all the open clients with the real time market data.
History
The concept of SignalR that is long polling or server side
scripting is not new in the world of Web. It is an existing technique which can
be achieve by Socket.IO, node.js and Nowjs. We could say SignalR is related to
this, but a new prospect that it is completely uses JavaScript on Client side
and ASP.NET on server side.