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State Pattern in ASP.NET MVC 3.0

I have a registration page in my application. It has 3 states and 1 error state(If any error comes):
Fill Basic Information
Select Package
Say Thanks
Error
Now I want to use state pattern here. First I created a console application which is OK. Now I want to implement this logic in my MVC application but I am confused about the structure. I mean how many views, models and controller I need and where to place my logic.

1 controller: RegistrationController
6 action methods:
GET+POST for Index (fill in basic info)
GET+POST for Package
GET for Thank you
GET for Error
This is rough code to make your mind going:
public class RegistrationController : Controller
{
public ActionResult Index()
{
RegistrationState model = RegistrationState.Init();
// just display the "Fill Basic Info" form
return View(model);
}
[HttpPost]
public ActionResult Index(RegistrationState data)
{
// process data and redirect to next step
this.TempData["RegState"] = data;
if (!this.ModelState.IsValid || data.State == State.Error)
{
// error should handle provided state and empty one as well
return RedirectToAction("Error");
}
return RedirectToAction("Package");
}
public ActionResult Package()
{
RegistrationState data = this.TempData["RegState"] as RegistrationState;
if (data == null)
{
return RedirectToAction("Error");
}
// get packages and display them
IList<Package> model = this.repository.GetPackages();
return View(new Tuple.Create(data, model));
}
[HttpPost]
public ActionResult Package(RegistrationState data)
{
// process data blah blah blah
}
// and so on and so forth
....
}
As you can see you still have to write some MVC-related code to act upon state changes. In my example everything's done in action methods. But action filters could be used as well. If you can't come up with a general action filter that can serve many different state objects then it's best to just write the code in action methods.
Another approach
If you know Asp.net MVC good enough you could take this a step further and write a state machine ControllerFactory that would work along with routing in a sense as:
{StateObjectType}/{State}
ControllerFactory would therefore be able to parse view data to a known state object type and pass execution to particular action. According to state. This would make it a specially state machine suited Asp.net MVC application.
The more important question is of course whether you can create the whole application with this pattern or are there just certain parts of it that should work like this. You could of course combine both approaches and provide appropriate routing for each.
Important notices
You should be very careful how you define your error state, because entering invalid field data shouldn't result in error state but rather in data validation errors that actually display within the view beside the field with invalid data (ie. invalid date provided as 13/13/1313). Your error state should only be used for actual object state error that's not related to user input. What would that be is beyond my imagination.
As mentioned in my comment you should check out some Asp.net MVC intro videos and you'll see how validation works in Asp.net MVC. Also rather simple stuff.
State pattern of this kind is not something a regular Asp.net MVC developer would use, because it would most likely complicate code more than taking the normal approach. Analyse before you decide. Asp.net MVC is very clean code wise so adding additional abstraction over it may become confusing. And your domain model (state classes) would most likely have a much more complex code as simple POCOs with data annotations.
In your case data validation would also be more complicated (when used with data annotations) because you object should be validated according to its state which may be different between states. POCO objects are always validated the same. This may mean that we may use more classes but they are smaller, simpler and easier to maintain.

I think you are confusing states. Examples of state are:
Awaiting for a user to register
User registered successfully
User didn't register successfully
Now each of these states would have a page:
localhost:8034/Register
localhost:8034/Register/Success
localhost:8034/Register/Failure
If user can't register because they left some fields empty, they will be in the first state and you will have to display some validation messages.
Because of this, as the minimum I'll have a controller called Register and the following action methods:
Index() GET/POST
Success() GET
Failure() GET

Routing by posted content type in ASP.NET MVC

I have a fixedURL to which I'd like to post different types of xml message, deserialized using DataContracts. Depending on the type of the deserialized message, I'd like to route to:
overloaded methods, e.g.
void Process(ContractType1 request) {}
void Process(ContractType2 request) {}
So at some point I need to deserialize this message and hopefully allow the default routing rules to match the correct method. Which extensibility point should I use for this? Or even better, can I make this work out of the box?!
If it makes any difference, I'm using MVC 3.

ASP NET MVC does not respect the overload if they are not decorated for different HTTP methods - e.g. one for POST, other for GET.
You need to use [ActionName(Name = "Process2")] to change the route name. And you will have to use different routes to access (if the HTTP methods are the same)
Have a look here.
Apart from the technical workaround, passing different contracts to the same URL is against the REST principles. Data could be in different format (XML, JSON, ...) but it must be the same. The URI defines a unique intention. Now it is possible to have a common dumpster where documents are all dumped to the same URI but then ASP NET MVC default model binder would not be able to help you and you need to create your own model binder.

Contrary to the other answer I say this is possible
Asp.net MVC is a great platform that can be easily extended. And so basically I've written a special action method selector that makes it possible to write overloads that can serve the same HTTP method but defer in parameters. By default you'd get runtime error that action method can't be resolved. But when you use this action method selector you get rid of this error.
Basically if your parameter classes have distinct parameter names, you can actually select methods by that.
Action method selector is called RequiresRouteValuesAttribute and a typical usage scenario would be with default route where id is optional in:
{controller}/{action}/{id}
This means that you either have to write
public ActionResult Index(int? id)
{
if (id.HasValue)
{
// display details view
}
else
{
// display master view
}
}
but by using my action method selector you can easily write two action methods:
public ActionResult Index()
{
// display master view
}
[RequiresRouteValues("id")]
public ActionResult Index(int id)
{
// display details view
}
The same could be applied to your action methods as long as your custom types have distinct property names or methods use different parameter names. So in your case it could be something like:
[RequiresRouteValues("first.Id")] // when you provide prefix with your form
// or
[RequiresRouteValues("Some.ContractType1.Distict.Property.Name")]
public ActionResult Process(ContractType1 first)
{
// do what's appropriate
}
[RequiresRouteValues("second.Id")] // when you provide prefix with your form
// or
[RequiresRouteValues("Some.ContractType2.Distict.Property.Name")]
public ActionResult Process(ContractType2 second)
{
// do what's appropriate
}
Read all the details about this action method selector and get the code as well.

ASP.NET MVC3 - How to serve View() from another controller

So in order accomplish what I asked in this post I did the following:
[iPhone]
[ActionName("Index")]
public ActionResult IndexIPhone()
{
return new Test.Areas.Mobile.Controllers.HomeController().Index();
}
[ActionName("Index")]
public ActionResult Index()
{
return View();
}
Which still serves the same view as the Index action method in this controller. Even though I can see it executing the Test.Areas.Mobile.Controllers.HomeController().Index() action method just fine. What's going on here? And how do I serve the Index view from Mobile area without changing the request URL (as asked in the original post referenced above)?

You have a few options:
Redirect to the Action you'd like to return: return RedirectToAction("Action-I-Want").
Return the View by name: return View("The-View-I-Want").
Note that with the 2nd approach you'd have to put your view in the "Shared" folder for all controllers to be able to find it and return it. This can get messy if you end up putting all your views there.
As a side note: The reason your work doesn't find the view is because default view engine looks for the view in the folder that "belongs" to the current executing controller context, regardless of what code you're calling.
Edit:
It is possible to group all "mobile" views in the same folder. On your Global.asax (or where ever you're setting up your ViewEngine, just add the path to your mobile View in the AreaViewLocationFormats. Mind you, you'll still have to name your views differently.
You can also write your own view engine. I'd do something like detecting the browser and then serving the right file. You could setup a convention like View.aspx, and View.m.aspx.
Anyhow, just take a look at WebFormViewEngine and you'll figure out what works best for you.

The easiest way to send a request to a view handled by another controller is RedirectToAction("View-Name", "Controller-Name").
There are overloads of View() that take route information that might work as well, but they'd require more effort to set up.

Well actually the easiest way is to make one version of your site programmed on standards instead of browser detection :D -- however in direct response to accomplish what it in a more of a ASP.NET mvc fashion, using:
RedirectToAction("ViewName", "ControllerName");
is a good method however I have found it is more practical if you feel you must program for different browser standards to create a primary view and an alternate "mobile" view under your controllers views. Then instead of writing special code on every controller, instead extend the controller like so.
public class ControllerExtended : Controller
{
private bool IsMobile = false;
private void DetectMobileDevices(){ .... }
}
Then modify your controller classes to instead say ControllerExtended classes and just add the one line to the top of each Action that you have alternate views of like so:
public class ApplicationsController : ControllerExtended
{
// GET: /Applications/Index
public ActionResult Index() {
this.DetectMobileDevices();
if(this.IsMobile){
return RedirectToAction("MobileIndex");
} else {
// actual action code goes here
return View();
}
}
}
Alternately you can use return View("ViewName"); but from my experience you want to actually perform different actions as opposed to just showing the result in a different view as in the case of presenting an HTML table as opposed to a Flex table to help iPhone users since there is no flash support in the iPhone, etc. (as of this writing)

how can i keep my url when my validation fail in asp.net mvc controller action

if i start off on a Detail page:
http:\\www.mysite.com\App\Detail
i have a controller action called Update which normally will call redirectToAction back to the detail page. but i have an error that is caught in validation and i need to return before redirect (to avoid losing all of my ModelState). Here is my controller code:
public override ActionResult Update(Application entity)
{
base.Update(entity);
if (!ModelState.IsValid)
{
return View("Detail", GetAppViewModel(entity.Id));
}
return RedirectToAction("Detail", new { id = entity.Id })
but now I see the view with the validation error messages (as i am using HTML.ValidationSummary() ) but the url looks like this:
http:\\www.mysite.com\App\Update
is there anyway i can avoid the URL from changing without some hack of putting modelstate into some temp variables? Is there a best practice here as the only examples i have seen have been putting ModelState in some tempdata between calling redirectToAction.

As of ASP.NET MVC 2, there isn't any such API call that maintains the URL of the original action method when return View() is called from another action method.
Therefore as such, the recommended solution and a generally accepted convention in ASP.NET MVC is to have a corresponding, similarly named action method that only accepts a HTTP POST verb. So in your case, having another action method named Detail like so should solve your problem of having a different URL when validation fails.
[HttpPost]
public ActionResult Detail(Application entity)
{
base.Update(entity);
if (ModelState.IsValid)
{
//Save the entity here
}
return View("Detail", new { id = entity.Id });
}
This solution is in line with ASP.NET MVC best practices and also avoids having to fiddle around with modestate and tempdate.
In addition, if you haven't explored this option already then client side validation in asp.net mvc might also provide for some solution with regards to your URL problem. I emphasize some since this approach won't work when javascript is disabled on the browser.
So, the best solution would be have an action method named Detail but accepting only HTTP POST verb.

The problem here is actually caused by your implementation. This doesn't answer your question, but it describes where you've gone wrong in the first place.
If you want a page that is used to update or edit an item, the URL should reflect this. For example.
You visit http:\www.mysite.com\App\Detail and it displays some information about something. That is what the URL describes it is going to do. In your controller, the Detail() method would return the Detail.aspx view.
To edit an item, you would visit http:\www.mysite.com\App\Edit and change the information you wish to update, the form would post back to the same URL - you can handle this in the controller with these methods:
[HttpGet]
public ActionResult Edit() {
MyModel model = new MyModel();
...
return View(model);
}
[HttpPost]
public ActionResult Edit(MyModel model) {
...
if (ModelState.IsValid) {
// Save and redirect
...
return RedirectToAction("Detail");
}
return View(model);
}
If you ever find yourself doing this...
return View("SomeView", model);
You are making your own life harder (as well as breaking the principles behind URLs).
If you want to re-use part of a view, make it a partial view and render it inside of the view that is named after the method on the controller.
I apologise that this potentially isn't very helpful, but you are falling into an MVC anti-pattern trap by displaying the same view from a differently named method.

As #Malcolm sais, best practice is to put ModelState in TempData, but don't do it manually! If you'd do this manually in every controller action where it's relevant, you would introduce immense amounts of repeated code, and increase the maintenance cost vastly.
Instead, implement a couple of attributes that do the job for you. Kazi Manzur has an approach (scroll down to the end of the post) that has been widely spread, and Evan Nagle shows an implementation with tests that is essentially the same as Kazi's, but with different names. Since he also provides unit tests that make sure the attributes work, implementing them in your code will mean little or no maintenance cost. The only thing you'll have to keep track of is that the controller actions are decorated with the appropriate attributes, which can also be tested.
When you have the attributes in place, your controller might look something like this (I deliberately simplified, because I don't know the class you inherit from):
[HttpPost, PassState]
public ActionResult Update(EntityType entity)
{
// Only update if the model is valid
if (ModelState.IsValid) {
base.Update(entity);
}
// Always redirect to Detail view.
// Any errors will be passed along automagically, thanks to the attribute.
return RedirectToAction("Detail", new { id = entity.Id });
}
[HttpGet, GetState]
public ActionResult Detail(int id)
{
// Get stuff from the database and show the view
// The model state, if there is any, will be imported by the attribute.
}
You mention that you feel putting ModelState in TempData feels like a "hack" - why? I agree with you that doing it with repeated code in every single controller action seems hacky, but that's not what we're doing here. In fact, this is exactly what TempData is for. And I don't think the above code looks hacky... do you?
Although there are solutions to this problem that might appear simpler, such as just renaming the action method to preserve the URL, I would strongly advise against that approach. It does solve this problem, but introduces a couple of others - for example, you'll still have no protection against double form submission, and you'll have pretty confusing action names (where a call to Detail actually changes stuff on the server).

The best practice you ask for is actually what you explained not to do: putting modelstate into tempdata. Tempdata is meant for it, that's why I would not call it a hack.
If this is to much repetitive code you could use the attribute modeldatatotempdata of MVCContrib. But the store is still TempData.

Handling post requests in ASP.NET MVC

Recently I started working with MVC, before that I used "classic" ASP.NET.
After using Ruby on Rails (RoR), I wonder how to implement POST request handling in MVC similar to how RoR operates. In RoR you use the Post method, so you need only one function for a view.
In ASP.NET MVC I need to use 2 separate functions for GET and for POST, so I need to initialize the same data twice, and I don't like to repeat something in my code.
How can I check if the request is POST in one method?
Update:
Solution is found: I have to use Request.HttpMethod.
Thank you!

I came across this question wanting to know the same thing. Below is a detailed description of my situation and the solution that I used (which utilizes the other answers provided here). I originally tried to use the two separate method approach, but I ran into a problem when the method signatures of these methods became identical.
I have a page that displays report data. At the top of the page there is a form with some fields, which allow the user to specify report parameters such as start date, end date, etc.
I originally approached this by creating two separate methods to handle the Get and the Post methods. The post method would redirect the browser to the get method so that any parameters that were specified would be added to the query string and so that the browser would not prompt the user with a dialog saying that it is going to resend the data that they entered if they refresh. Note: I realized later that I could accomplish this by setting the method attribute of my form element to "Get", but I think ideally a controller shouldn't have knowledge of how a view is implemented, so in my opinion that is irrelevant.
As I developed these two methods I eventually found myself in a situation where the method signatures became identical. Furthermore, my code for these two methods became nearly identical, so I decided to merge them into a single method and to just check the request verb so that I could do something slightly different when the request is not a "Get". A distilled example of my two methods is shown below:
// this will not compile because the method signatures are the same
public ActionResult MyReport(DateRangeReportItem report)
{
// if there are no validation errors and the required report parameters are completed
if (ModelState.IsValid && report.ParametersAreComplete)
{
// retrieve report data and populate it on the report model
report.Result = GetReportData(report.CreateReportParameters());
}
return View(report);
}
[AcceptVerbs(HttpVerbs.Post)]
public ActionResult MyReport(DateRangeReportItem report)
{
if (ModelState.IsValid && report.ParametersAreComplete)
{
// redirect to the same action so that if the user refreshes the browser it will submit a get request instead of a post request
// this avoids the browser prompting the user with a dialog saying that their data will be resubmitted
return RedirectToAction("MyReport", new { StartDate = report.StartDate, EndDate = report.EndDate });
}
else
{
// there were validation errors, or the report parameters are not yet complete
return View(report);
}
}
Why am I accepting a model object as the parameter to my get method? The reason is that I wanted to take advantage of the validation logic already built into the model object. If someone navigates to my page directly with all parameters already specified in the query string, then I want to go ahead and retrieve the report data and display it on the page. However, if the parameters specified in the query string are invalid then I also want validation errors to appear on the page. By putting my model object as the parameter, the MVC framework will automatically attempt to populate it and will capture any validation errors without any additional work on my part.
I used the other answers posted for this question to create a RequestHttpVerb property on a base controller class in my project:
public HttpVerbs RequestHttpVerb
{
get { return (HttpVerbs)Enum.Parse(typeof(HttpVerbs), this.Request.HttpMethod, true); }
}
So finally my consolidated method looks like the following:
[AcceptVerbs(HttpVerbs.Get | HttpVerbs.Post)]
public ActionResult MyReport(DateRangeReportItem report)
{
// check if there are any validation errors in the model
// and whether all required report parameters have been completed
if (ModelState.IsValid && report.ParametersAreComplete)
{
// this is unnecessary if the form method is set to "Get"
// but within the controller I do not know for sure if that will be the case in the view
if (HttpVerbs.Get != this.RequestHttpVerb)
{
// redirect to the same action so that if the user refreshes the browser it will submit a get request instead of a post request
// this avoids the browser prompting the user with a dialog saying that their data will be resubmitted
return RedirectToAction("MyReport", new { StartDate = report.StartDate, EndDate = report.EndDate });
}
// there were no validation errors and all required report parameters are complete
// retrieve report data and populate that data on the model
report.Result = GetReportData(report.CreateReportParameters());
}
// display the view with the report object
// Any model state errors that occurred while populating the model will result in validation errors being displayed
return View(report);
}
That's my current solution to the problem. I would prefer not to have to check the Request.HttpMethod property in order to determine whether I needed to perform the redirect, but I didn't see another solution to my problem. I would have been fine with keeping two separate methods to handle Get and Post requests, but the identical method signature prevented this. I would have preferred to rename my Post action handler method to avoid the method signature conflict and to use some mechanism to indicate to the MVC framework that my renamed method should still handle the "MyReport" action, but I am not aware of any such mechanism in the MVC framework.

You only need separate methods for GET and POST if their method signatures differ, there's no reason why one action method can't handle GET and POST methods.
If you need to know whether it was a GET or POST, you could check using Request.HttpMethod in your action, but I would advise using a separate method decorated with the [AcceptVerbs(HttpVerbs.Post)] attribute as suggested by the other posters.

You don't check in ASP.NET MVC. You decorate your method with the [AcceptVerbs(HttpVerbs.Post)] attribute to indicate that the method applies to post only, and accept the model in the method used to handle the post.
I'd strongly suggest doing the walkthrough for NerdDinner to understand more about the ASP.NET MVC framework.

You may take a look at the Request.HttpMethod property.

Correct way to do is using ModelBinding during Post request.
[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Edit(EmployeeViewModel model)
{
//validate data, save employee, handle validation errors...
}
This way you will not have to init your data again.