I'm having difficulty grasping the concept of MVC within .NET. I'm creating a basic Blog application, mainly to gain insight and skills with MVC. I just don't quite get some of it. The part I am currently unclear about is the relationship between a Controller and View. It would clear the matter up if someone would answer me this.
I have a View called TestA which corresponds to my Controller ControllerTestA. Now I've added the following inside the ControllerTestA.
public ActionResult TestA (){ //do something }
Now I need to know if all my postbacks in whatever form from view TestA will have to go through my TestA Controller method. So essentially I could have different postback with different parameters for different reasons. Some in use with one postback and others in use for another. Is that how it is done?
Would love some assistance here.
You are missing a crucial part of the relationship here, which is routing. You are speaking in terms of WebForms using terms like Postback; don't do that because you'll end up confusing yourself.
The best way to think about MVC is in Requests and Responses.
Let's look at how a request (high level) happens in an MVC application.
Request
Request hits the server with a url ex. /hello/world
That url is used to match any entries in your route table
When a match is found, that route defines basic values like what controller and action should be called.
The controller is created, and that action is called with the route values and other request properties (querystring, session, etc...).
Response
We are now in the controller action, run the code you need to fulfill the request
Pass the data to the View
The view is determined by convention and your ViewEngine
The view is then rendered and written to the response.
The request/response is finished.
Note
This whole process is determined by the route, and the relationship between the controller and view are trivial. Where the form is posted to is determined by you in the view by using helper methods that determine what route to hit in the next request/response flow.
Some Helper Methods.
#Url.Action("index", "home");
#Html.ActionLink("index", "home")
#using (Html.BeginForm("create", "home")) { }
To sum it all up, the relationship between the controller action and view is really facilitate by your routes. Once you have a grasp of how to create them, then you will better understand how to manage the interaction of your application. Hope that helps. :)
There is no such thing as "Postback" in MVC. In contrast to WebForms, a view only renders HTML to be sent to the browser. As soon as any type of request is issued by the browser, it goes to the controller, not to the view.
As for the relationships:
If you define a TestAController (note: Not "ControllerTestA"), it serves the "/TestA/*" URL's. If you have a method TestA in there it will serve "/TestA/TestA".
If your method returns View(someModel) it will look for a view named TestA.cshtml/TestA.aspx, named like your method, within a folder Views\TestA (named like your controller, without the "Controller" suffix)
The view will render the HTML based on the someModel passed by the controller.
Within the view you may call other URL's or post data to some. This closes the circle.
As for the parameters or overloads, there are some restrictions:
You can define overloads for GET vs. POST vs. PUT vs. DELETE. You will need to annotate the methods with the according attributes though.
However you cannot define multiple overloads of the same method name for POSTs with different sets of parameters. You will need to make your POST method signature such that parameters can or cannot be sent to the server:
Example:
public ActionResult TestA(
string someOptionalParameter, int? someOtherOptionalParam)
{
if (string.IsNullOrEmpty(someOptionalParameter)) { ... }
if (someOtherOptionalParam == null) { ... }
}
The model-mapper will set your parameters to null if they are not posted to the server.
Like Khalid already mentioned - you should not mix up the concepts of MVC and WebForms. They are very different. MVC has no such thing as a "view state" which could be posted to the server. It has no WebForm-like lifecycle for the ASPX (or CSHTML) pages.
If you have a form in a view, then that form has a url to which it will post to. This URL is in the Html.BeginForm method in your view.
The form will then be posted to the appropriate controller methond in the approoriate controller
So if BeginForm starts like this:
using (Html.BeginForm("AddProduct", "Product"
Then the action method "AddProduct" in the controller Product (ProductController is the class name) will be called.
Related
I just came across this topic in a current project and I would like to know the best way to handle the "problem" of objects getting lost, when using the HttpPost method when submitting a form. Thoughout the web and the posts on stackoverflow I gathered some ways to deal with it.
So, once I got that a view model gets objects or lists from the HttpGet request they are lost because of the stateless nature of http. I now have seen different approaches to get that objects back when passing the view model back to the view.
Store objects in hidden field
#Html.HiddenFor(m => m.Object)
This seems to be working fine if the view models property is serializable. But what if there is logic behind the objects? Will this work for all scenarios? And on the other hand, I don't want every object inside my view model, just the ones for display and the user can interact with.
Get the object via AJAX and HelperMethods
#Html.Some3rdParty().ComboBoxFor(m => m.List)
.DataSourceUrl(#Url.Action("GetComboSource"))
[ComboBoxSource]
public ActionResult GetComboSource()
{
var data = Service.GetStaticSource();
return Json(data);
}
Using 3rd party libraries like Kendo UI MVC I can easily put a .DataSourceUrl() HtmlHelper on my control for requesting a controller to provide the datasource. Or just using jQuery's $.get() method. The problem is: What if I can't use such a library or the requirement says, that JS has to be avoided as much as possible?
Get the object back in the HttpPost Controller action
[HttpPost]
public ActionResult Edit(ViewModel viewModel)
{
var tempViewModel = Service.GetViewModel(viewModel.Id);
viewModel.Object = tempViewModel.Object;
return View(viewModel);
}
This one seems a bit brittle to me. On the post action I have to call whatever service provides the view model, extract certain objects and attach them to my recieved view model.
Currently that's all I can think of, but in short:
I'd like to know, what is the best practise to handle it throughout a project and what's the best way for maintainability?
For me it seems there is no perfect solution so far. How do you do it in your projects?
Avoid solution 1: you will weigh your requests, the data can be forged and if your object is not serializable (or the to string method does not provide useful string) you will have some problems. If you want to use something similar prefer Session
Solution 2: I use ajax populating when the input have to be filtered depending of other controls value. If it is not the case you will have controller with lot of actions and not easily maintanable.
Solution 3 is the one I use and I prefer because it is more DRY, more secure (no forgery), and keeps the controller light.
Just change
<input class="ui-input-text " type="text" id="PlateNo" tabindex="2" name="PlateNo">
to
<input class="ui-input-text " type="text" id="PlateNo" tabindex="2" name="PlateNo" value="#Request["PlateNo"]">
You can be show on the textbox sending value for this input.
Only add value="#Request["yourinputname"] to your input.
In my requirement, all views should be able to display notifications based on what happened within Actions in the controllers. The implementation as it stands is in a BaseModel which is inherited by all Models needing to show notifications. Then, any view with this requirement simply calls:
#{ Html.RenderPartial("MessageCtrl", Model); }
And a notification is rendered. This works fine in cases where an Action is returning a view directly, and is usually handled like this in an Action:
model.SetMessage(response);
return View(model);
...where SetMessage updates the notification related properties of the model from an object returned from my service. All responses implemented an interface I created called IResponse, so messaging can be handled throughout.
The problem arrises when I need to return a View from a different Action and still show a notification.
For example, on my EditUser action, if edit was successful, I want to show the Index view. To achieve this from the EditUser action, I need to return RedirectToAction (because simply returning the view will return the correct view with the incorrect URL indicating it is EditUser when it is not). However, RedirectToAction loses all notion of my model and BaseModel, so by the time it redirects, it has lost my notification. I know I can use RouteValues, but that defeats the purpose of having a common base model driven notification approach. I even looked at the ViewBag (usually I dismiss it as the ugly part of MVC), but found that ViewBags only persist for the life time of a single request, and using RedirectToAction, the ViewBag is empty again by the time it hits the target Action. Another thought was to store it in a session object, but that sounds downright ugly to me.
This seems like its a pretty standard requirement. Is there a standardised approach to passing common data (like notifications) around to different views asside from through the querystring through a RedirectToAction?
I think you are looking for TempData which only persists data in session across one redirect.
I'm converting a legacy webforms app to MVC, working through it a page at a time. To make the project easier to work with I've moved all the webforms pages, which were previously in the route of the project into a /webforms subdirectory. So I need to capture any incoming requests for /page.aspx?param=123 and redirect them to /webforms/page.aspx?param=123. I thought an easy way to do this would be to setup a route handler that passed any such requests to a controller that does that job. I set up a route like so:
routes.MapRoute("WebformsRedirect", "{*page}",
new { controller = "Webforms", action = "ForwardToPage" },
new { page = #"\S+.aspx\S*" }
);
This kind of works but it doesn't capture the query string, only the page part. I can get the query string for the Request object in the controller so it's not a huge deal but it would be nice to be able to do it through the route only. My routing unit tests (which I copied from Steve Sanderson's MVC book) actually pass correctly when I test them with querystrings so I'm confused why it isn't working. Is my regular expression wrong? They aren't my strong point.
QueryStrings are not part of the routing
if you requested for example "Home/Index?foo=bar" and you have a route that match "Foo/Bar" to Controller Foo , Action Bar without any more routing info (don't know anything about foo) you still can write
class HomeController: Controller {
ActionResult Index(string foo) {
}
}
now foo variable will equal bar , why ?
because its the model binder that gets the value of the parameters passed.
the model binder check 4 repositories by default QueryString , Routing Place Holders ,FormsCollections and Files
so what i am trying to say , the route and QueryStrings are two different things , it doesn't need to capture it
If this is a duplicate, please let me know - because i had a quick look and couldn't find anything that really answers my question.
I'm experimenting with ASP.NET MVC 2. Now coming from a Web Forms background, i only really dealt with HTTP GET and HTTP POST.
I'm trying to see how i could apply GET/PUT/POST/DELETE to the respective CRUD operations on my repository (Find, Insert, Update, Remove).
Say i have a single controller, with the following action methods:
[HttpGet] // GET: /Products/{id}
[ActionName("Products")
public ActionResult Get(int id = 0) { ... }
[HttpPut] // PUT: /Products
[ActionName("Products")
public ActionResult Put(Product product) { ... }
[HttpPost] // POST: /Products/{product}
[ActionName("Products")
public ActionResult Post(Product product) { ... }
[HttpDelete] // DELETE: /Products/{product}
[ActionName("Products")
public ActionResult Delete(Product product) { .. }
Couple of questions on that - is that how you would name/separate the action methods? Should i be passing through the entire model (Product), or just the id?
The problem i'm having is i'm not sure how to handle invoking these action methods with the relevant HTTP Verb in my View.
At this stage, I'm thinking i would have 3 Views:
"Index" - bind to IEnumerable<Product> model, listing all products, with "Edit", "Details" and "Delete" links
"Single" - bind to single Product model, listing all details for a product, with an "Update" button.
"New" - bind to single Product model, with form for creating product, with an "Create" button.
So - my question is, how do i specify i want to invoke a particular controller method with a specific HTTP Verb?
With Html.BeginForm, you can specify a FormMethod enumeration - but it only has GET and POST.
How can i perform a PUT and DELETE command?
Will i need a seperate View for each HTTP Verb?
If i have a link called "Delete", can i invoke a HTTP DELETE command to my controller, or does it need to be redirected to a new View with the form action delete?
Or, is this a silly/overkill design in the first place, should i just stick with "GET" and "POST"?
I'm (fairly) new to this style of web development (REST), so please be kind. :)
UPDATE
So i came across this interesting article from Stephen Walther, regarding this very topic.
He indicates a HTML Form only supports GET and POST (because i'm new to REST-style web development, i did not even know this, to which i am partially ashamed).
Apparently the only way to invoke a Controller action with PUT/DELETE is to do it with AJAX. Seriously?
So what should i do here, should i stick with GET/POST, or should i create a JavaScript file which wraps the underlying XmlHttpRequest code behind a nice function?
Which way are ASP.NET MVC developers leaning? Surely someone has asked themselves this same question.
The reason that you're mostly familiar with GET and POST is because a regular old browser can only GET or POST a URL, especially when submitting a form.
Setting up your controllers this way, you're looking at something more along the lines of a REST API vs. a web site at least in spirit.
And yes, you are correct that only AJAX requests can set their request methods explicitly, so you're good to go if you'll be performing actions like deleting products via AJAX (in which case I would suggest only passing the ID since it is much lighter than serializing the entire product and you'll likely have easy access to the ID in your markup).
Here's the thing. If you are building a modern web application you're probably using AJAX and without getting too dogmatic you should expect your users to have JavaScript. If you want to do CRUD without AJAX then you can always POST a Product or use GET for a delete method with the ID in the URL (caveat to that, make sure the Delete method is protected behind authorization or a web crawler will gladly consume your GETs and delete all your data...)
If you don't want to build a REST API then don't sweat the fact that you're not using DELETE (just use GET with the ID in the URL) or you're not using PUT (just use POST with the product entity in the POST body).
REST is a great style for building APIs (no presentation tier, data sent in raw format to clients who consume them, could be a phone or a website, etc.) over HTTP. HTTP is great on its own for building web pages. Use what you need for what you need it for.
If you want to build a REST API to be used by both other people AND your web site, then do that, and just have your site's controller action methods call your API methods directly. I do that all the time. Use a web client like Hammock to make it easier on you.
Personally I stick to as simple as possible full requests, instead of going AJAX all over. I use ajax, but in specific places where it enhances the experience (and I do with a progressive javascript approach).
Because of the above, I always just use GET and POST.
As for the naming, for those I'd do: Get, Update, Create, Delete, which makes it pretty clear. I actually use more like an action name that's related to what the operation does, but for simple things those work fine.
HtmlHelper.HttpMethodOverride Method (System.Web.Mvc)
How about this?
I have created a controller that does some business logic and creates a model. If I pass this model directly to view by returning ModelAndView with view name and model - everything working great. But now I want to display results at another page. So I use "redirect:" prefix to redirect to another controller, but the model is lost.
What Im missing?
Regards,
Oleksandr
you can use the forward: prefix which ultimately does a RequestDispatcher.forward()
insted of The redirect: prefix.
Option 1 :
You might put the model in session and get it back in the controller and nullify it in session.
Option 2 :
You said, you are having two controllers, first one would retrieve the user input and do some business logic and redirect to other one. My suggestion is to move the business logic which is placed in both controllers to a class and have only one controller which would return the model and view to the user.
During redirect: request is sent using GET method with parameters appended to the url. You can right a new method in the controller to receive the request parameters with #RequestParameter annotation.
While redirecting the request simple add all the parameters as string
e.g ModelAndView mv = new ModelAndView();
mv.setViewName(redirect:/your/url);
mv.addObject("param1", string_param);
.
.
.
This way you can redirect successfully.
Since the redirect: prefix runs another controller, you will lose whatever you had in the ModelAndView in the previous controller. Perhaps the business logic controller should not be a controller at all -- maybe you should just make it a regular class, and have the results controller call it. Then the results controller could save the data to the model.
i would not use #SessionAttributes as it may change in future releases of spring. I would stick with the old fashioned way that Oleksandr showed you above
somehow an old post but maybe someone else will find it usefull