public JsonResult getJson()
{
Customer obj = new Customer();
obj.CustomerCode = "c001";
return Json(obj,JsonRequestBehavior.AllowGet);
}
Please do once run the controller withthe above JSON action to check if the JSON result is displayed properly. If you are using chrome the display comes on the browser , if its internet explorer it spits out a file.
In case you are new to Jquery , please read this What is jquery ?
The next step is to consume the JSON data in Jquery using MVC view. So go ahead and add a view for example my view name is “LearnJquery.aspx”.
First thing add the Jquery library at the top of the ASPX page. In case you do not find jquery library in your project that means you have not created the MVC project using the basic template.
<script src="../../Scripts/jquery-1.8.2.js"></script>
You can then make a call the controller which is exposing in JSON format using “getJson” method as shown below. Its takes three parameters:-
$.getJSON("/Json/getJson", null, Display);
function Display(data)
{
alert(data.CustomerCode);
}
The complete MVC view HTML looks as shown below. I have created a simple HTML button and on the click event I am calling a “getJson” javascript method which makes a call to the JSON controller and displays the JSON data in a javascript alert.
<script language="javascript">
function getJson() {
$.getJSON("/Json/getJson", null, Display);
return true;
}
function Display(data)
{
alert(data.CustomerCode);
}
</script>
<input type="button" value="See Json data" onclick="return getJson();"/>
This view I have invoked by using “DisplayJson” action.
public class JsonController : Controller
{
public ActionResult DisplayJson()
{
return View("LearnJquery");
}
}
After you have done all the hardwork its time to hit the “DisplayJson” action to see the beauty running.
The primary goal of MVC is to create web applications and web applications use HTTP protocol. Now HTTP protocol is a stateless by nature. So when you send a request to MVC application it serves the request and forgets about the request. Next time when the same user sends the request MVC treats that as a complete new request.
Now think about the below situation:-
In short we need to have some kind of mechanism which will help us to remember states between request and response of MVC.
There are 3 ways of maintaining states in MVC and these ways can be used depending from which layer to which layer you navigate.
Temp data: -Helps to maintain data on redirects for a single request and response. Now the redirects can be from controller to controller or from controller to view.
View data: - Helps to maintain data when you move from controller to view.
View Bag: - It’s a dynamic wrapper around view data. When you use “Viewbag” type casting is not required. It uses the dynamic keyword internally.
Session variables: - By using session variables we can maintain data until the browser closes.
Let’s demonstrate the above fundamental with a demo.
Add two controllers “DefaultController1” and “DefaultController2”.
In the “Default1Controller” in “Action1” we set session,tempdata,viewdata and viewbag values as shown in the below code snippet. Once we set the values we do a redirect to the action “SomeOtherAction” which belongs to “Controller2”.
public class Default1Controller : Controller
{
//
// GET: /Default1/
public ActionResult Action1()
{
Session["Session1"] = "UntilBrowserCloses";
TempData["FortheFullRequest"] = "FortheFullRequest";
ViewData["Myval"] = "ControllertoView";
ViewBag.MyVal = "ControllertoView";
return RedirectToAction("SomeOtherAction","Default2");
} }
In “Default2Controller” we will try to read values set in “Default1Controller”. Once the values are read we invoke a view called as “SomeView”.
Please note I am setting “ViewData” and “ViewBag” before redirecting to the view.
public class Default2Controller : Controller
{
//
// GET: /Default2/
public ActionResult SomeOtherAction()
{
string str = Convert.ToString(TempData["FortheFullRequest"]);
string str2 = Session["Session1"].ToString();
string str3 = Convert.ToString(ViewData["Myval"]);
ViewData["Myval"] = "ControllertoView";
ViewBag.MyVal = "ControllertoViewCollection";
return View("SomeView");
}
}
The “SomeView”view justdisplays the data present in “TempData” ,”ViewData” , “ViewBag” and “Session” .
<%= TempData["FortheFullRequest"] %><br />
<%= ViewData["Myval"] %><br />
<%= Session["Session1"] %>
<%= ViewBag.MyVal %>
<a href="/Default1/Action1">Click</a>
So let’s put debug points in both the controller actions and let’s hit Default1 controller and Action1 action http://localhost:1203/Default1/Action1 . So in this action session,tempdata ,viewdata and viewbag are loaded. Below is how the watch window looks with data.
Now from here we are redirecting to controller2 action “SomeOtherAction”.
In controller2 you can see get “TempData” and “Session” variables but not “ViewBag” and “ViewData”( See “str3” and “str4” are set to null). In other words “ViewData” and “ViewBag” do not persist data in redirects while “TempData” and “Session” variables do.
I have set “ViewData” and “ViewBag” with some data again before invoking the view “SomeView”.
When the view gets invoked we can see all the data. In other words “ViewData” and “ViewBag” persist data from controller to view. And also tempdata and session have persisted data.
Now when the view invokes I have kept a click hyper link which invokes “Action1” from “Controller1”. This is to simulate a fresh request.
When we click on the link. All the other variables go off only session variables persist, see the below figure. It means “Session” variables can persist between requests.
Below is a summary table which shows different mechanism of persistence.
| Maintains data between | ViewData/ViewBag | TempData ( For single request) | Session |
| Controller to Controller | No | Yes | Yes |
| Controller to View | Yes | Yes | Yes |
| View to Controller | No | No | Yes |
MVC applications at the end of the day are web applications which are hosted inside IIS.Now when any request comes to MVC controller it pulls up a thread from thread pool and serves that request. In other words IIS web server maintains a pool of threads rather than creating threads from scratch again and again to gain performance benefits.
Let’s assume that a web server has a thread pool size of 2. Now this is just an assumption because a pool size of two is very much hypothetical. But to make things simple consider that the thread pool size is 2.
So let’s say first request comes to the site, IIS pulls up a readymade thread object from the thread pool and starts serving that request. In the meantime let’s say second request comes in so again IIS pulls up a thread from the thread pool and starts serving the second request.
Now the fun starts when third request comes in. The IIS webserver does not have any more thread objects in the pool as those are already serving “request1” and “request2”. So he just moves the third request in to a waiting mode or the server can send “503 busy” message to the client.
This situation is termed as “Thread Starvation”. Thread starvation situations can be overcome by making the request “Asynchronous”. So the request comes in and immediately the request is processed in an “Asynch” manner and releasing the thread serving the request immediately.
So to avoid this we can achieve the same by making our controllers “Asynch”.
Below is a nice video which demonstrates MVC Thread starvation.
So let’s understand step by step how to implement MVC Asynch controllers.
Consider the below controller class “HeavyController” which has an action “SomeHeavyMethod” and this action waits for 20 seconds. So let understand how we can make this simple controller aasynch controller.
public class HeavyController : Controller
{
//
// GET: /Heavy/
public ActionResult SomeHeavyMethod()
{
Thread.Sleep(20000);
return View();
}
}
So the first step is to inherit from “AsyncController” class.
public class HeavyController : AsyncController
{
}
The next step is to append “Async” word after the methods. So you can see “SomeHeavyMethod” has been changed to “SomeHeavyMethodAsync”.
The heavy logic code i.e. “Thread.Sleep” is moved to a different method and that method is invoked using task parallel library from the “SomeHeavyMethodAsync”.
Every time a “Task” or a “Thread” is started we increment the outstanding operations counter by using “AsynchManager” and every time a multi-threaded task is completed we decrement the counter.
public class HeavyController : AsyncController
{
public void SomeHeavyMethodAsync()
{
AsyncManager.OutstandingOperations.Increment();
Task.Run(new Action(Heavy));
}
public void Heavy()
{
Thread.Sleep(20000);
AsyncManager.OutstandingOperations.Decrement();
}
}
Now once all the multi-threaded tasks complete and the outstanding operations are zero we need to return the view. So for the same we need to create an action result method with “Completed” word appended. This method gets called when all outstanding operations are zero.
public ActionResult SomeHeavyMethodCompleted()
{
return View();
}
Also ensure you add “SomeHeavyMethod” view with some text on it.
<html>
<head runat="server">
<meta name="viewport" content="width=device-width" />
<title>Some heavy method</title>
</head>
<body>
<div>
This is loaded after some time....
</div>
</body>
</html>
Now try hitting “Heavy/SomeHeavyMethod” and see the output. I would suggest you to measure “Thread queued” to see the benefit of asynch controller. Watch this video to see how to measure “Thread Queued” http://www.youtube.com/watch?v=wvg13n5V0V0.
Still working on it.
Final note, you can watch my c# and MVC training videos on various sections like WCF, Silver light, LINQ, WPF, Design patterns, Entity framework etc. By any chance do not miss my .NET and c# interview questions and answers book from www.questpond.com .
For technical training related to various topics including ASP.NET, Design Patterns, WCF, MVC, BI, WPF contact SukeshMarla@gmail.com or visit www.sukesh-marla.com
Start with MVC 5
In case you want to start with MVC 5 start with the below video Learn MVC 5 in 2 days.
In case you are going for interviews you can read my 50 Important MVC interview questions with answer article http://www.codeproject.com/Articles/556995/Model-view-controller-MVC-Interview-questions-and
In case you are completely a fresher I will suggest to start with the below 4 videos which are 10 minutes approximately so that you can come to MVC quickly.
Lab 1:- A simple Hello world ASP.NET MVC application.
Lab 2:- In this Lab we will see how we can share data between controller and the view using view data.
Lab 3 :- In this lab we will create a simple customer model, flourish the same with some data and display the same in a view.
Lab 4 :- In this lab we will create a simple customer data entry screen with some validation on the view.
- The first parameter in “getJson” is the MVC JSON URL with complete controller/action path format.
- The second parameter is the data to be passed. For now its NULL as we are more interesting in getting JSON data rather posting data.
- The last parameter is the call back method (“Display”) which will be invoked once we get the JSON data from the controller. The “Display” function is also available in the below code snippet. I am just putting an alert with the property name. FYI you can see how I have just typed “data.CustomerCode” , no parsing nothing the JSON data is automatically translated to javascript object.
- End user sends request to a MVC site.
- MVC sends a login page.
- User enters proper details and sends data to the MVC application.
- MVC validates the user and sends home page of the site. MVC application now forgets everything about the user as it’s stateless.
- Now user clicks on one of the home page links. This is sent to the MVC application and because MVC application has forgotten everything about the user, he sends a login page again for authentication….User would feel Weird…
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