I am attempting to construct an asp.net mvc app which will use the urls like:
/Controller/[Number]/Action/Id
I have got it to always call my controller and pass it the Number and the Id fine...
However I now want to return a different view depending on the Number
I could have options like:
if([Number] == 1) { return View("ViewName");}
if([Number] == 2) { return View("ViewName2");}
however I instead was wondering if there was a way to change the core so that instead of searching at ~/Views/controller/action.aspx I could have my own method which did some checking on the Number then passed to the virtual file provider is a different path
Hope this makes sense!
Decide which view to load, depending on input parameters is a controller task. You could write your own view engine.
But it is easier to return the full path to the view you want to return.
return View("~/myviews/ViewName3.aspx");
This will render ViewName3 from given directory.
You might want to look at decorating your controller method with Action Filter Attributes.
Then, you could do something special inside the Action Filter Attribute.
Or, you could pass Number to a Model object, then have the model Object return the right View path.
Either way, your instinct of trying to keep too much logic out of the Controller is sound, especially if [Number] is somehow a business concern and not a view concern.
You need to look into / google creating a custom view engine.
By the sounds of things you probably just want to extend the built-in WebFormViewEngine and just override the locations and the .FindView() method.
HTHs,
Charles
Related
I need to pass objects between ActionMethods and Views in an ASP.net MVC 5 app.
I'm using it for a multi page signup - and for a multi page payment.
Is this bad practice? I haven't seen a good way to pass objects between different controllers.
Code:
public ActionResult Join1()
{
//
return View("Join2", MyObject);
}
[HttpPost]
public ActionResult Join2(MyObject MyObj)
{
//manipulate object
//return
}
It seems to be an effective way to do it - though I haven't seen many people do it this way. I haven't seen objects being passed between action methods much at all.
Is there a flaw in this approach, a better way of passing models between Views - or should each ActionMethod stick to passing simple data with, say, TempData instead of objects?
Why haven't I seen any sample projects doing things like this?
I've seen return RedirectToAction("act"); plenty - but that is Get and passing an object in a URI is limiting - and I don't want users to be able to manipulate or see the data being passed.
thx.
Unless I have misunderstood the description, your code is not doing what you think it's doing. That first return View("Join2", MyObject); statement is not executing the second ActionMethod, it is only passing your data into the View that happens to have the same name as the second method. Therefore the code implied by //manipulate object will not run before that View is rendered and sent back to the user.
Assuming the View file Join2.cshtml exists, and it contains the default #using (Html.BeginForm()), then users submitting the form will cause the Join2 Action to be executed and the same view rendered with the manipulated data - unless, of course, you add another return View() statement that names a different View.
The reason you haven't seen this done much is that the MVC convention is to have a View named the same as the ActionMethod, this makes the code slightly simpler and also much easier for other ASP.NET developers to understand because it is what they are expecting to see.
If you want the form rendered by each View to then execute a different ActionMethod when it is posted back, the place to do that is in the View code, where Html.BeginForm() has several overloads that allow you to do just that, e.g. in Join.cshtml you could write:
#using (Html.BeginForm("Join2", "JoinController"))
{
// form fields and stuff
}
// Produces the following form element
// <form action="/JoinController/Join2" action="post">
To address the final part of your question, "I don't want users to be able to manipulate or see the data being passed", sorry to say it but your proposed code doesn't prevent that: users can see the data in the web form, before it is ever posted back to the Join2 method; they can manipulate the data by sending an HTTP POST containing any data they want back to the Join2 method.
If you absolutely, positively need to actually execute Join2() from within Join(), before anything is passed back to the user, then you can call it just like any other C# method:
var myResult = Join2(MyObject);
Then you have an ActionResult object that you can manipulate or return straight to the browser. But why you would want to do this, is beyond me.
Should we move logic that supposes to be in Controller (like the data to render the partial view) to ActionFilter?
For example, I'm making a CMS web site. There should be a advertisement block to be rendered on several pages but not all the pages. Should I make an ActionFilter attribute like [ShowAd(categoryId)] and decorate the action methods with this attribute?
The implementation of this controller would include service calls to retrieve information from database, buildup view models and put in the ViewData. There would be a HtmlHelper to render the partial view using the data in ViewData if it exists.
That just seems yucky to me.
When I'm trying to figure out whether I need an ActionFilter, the first question I have is, Is this a cross-cutting concern?. Your particular use-case doesn't fit this, at first blush. The reason is, is that an ad is just another thing to render on a page. There's nothing special about it that makes it cross-cutting. If you replaced the word 'Ad' with 'Product' in your question, all the same facts would be true.
So there's that, and then there's the separation of concerns and testability. How testable are your controllers once you have this ActionFilter in place? It's something else you've got to mock out when testing, and what's worse is that you have to mock out those dependencies with every controller you add the ActionFilter to.
The second question I ask is, "How can I do this in a way that seems most idiomatic in the platform I'm using?"
For this particular problem, it sounds like a RenderAction and an AdController is the way to go.
Here's why:
An Ad is its own resource; it normally isn't closely tied to anything else on the page; it exists in its own little world, as it were.
It has its own data-access strategy
You don't really want to repeat the code to generate an Ad in every place you could use it (which is where a RenderPartial approach would take you)
So here's what such a beast would look like:
public AdController : Controller
{
//DI'd in
private AdRepository AdRepository;
[ChildActionOnly]
public ActionResult ShowAd(int categoryId)
{
Ad ad = Adrepository.GetAdByCategory(categoryId);
AdViewModel avm = new AdViewModel(ad);
return View(avm);
}
}
Then you could have a custom partial view that is set up around this, and there's no need to put a filter on every action (or every controller), and you don't have try to fit a square peg (an action filter) in a round hole (a dynamic view).
Adding an Ad to an existing page then becomes really easy:
<% Html.RenderAction("ShowAd", "Ad" new { categoryId = Model.CategoryId }); %>
If your ad system is simple enough, there is no reason you could/should not use an action filter to insert enough info into the view data to generate the ad in your view code.
For a simple ad system, say.. a single ad of a specific category shows up in the same place in the layout on every page and that's it, then there is no real argument of a better way except to prepare for future changes to the system. While those concerns may be legitimate, you may also have it on good authority that requirement will never change. But, even if requirements do change, having wrapped all the code that generates ads in one place is the most important aspect and will save you much more time up front than a more robust solution might. Obviously there are more than a few ways to wrap this code in a single place.
As for the way you are choosing to do it, I would keep your action filter cleaner to only have it insert the category into the view data and have all the magic happen inside your html helper which would take the category in as a parameter. Building up view models to shove into the view data is going to require a bit of extra work, and put code all over the place when it doesn't need to be there. Keep it simple and do all of the html generation inside of the html helper which is responsible for...building html.
I'm working on an ASP.NET MVC controller with several action methods, all of which need the same bit of data. This data requires a lookup that can only be done with the route values (so, I can't do the lookup in the constructor). I'm sure this has been discussed at length, but I've yet to find a satisfactory recommendation.
What's the best way to get this data without repeating myself in each action method? I'm working through:
Create an Action Filter, this seems like the best bet, but where do I store the object, in the action parameters? Is it appropriate to create a ViewModel object in an action filter and pass it directly to the action methods, for them to fill out the rest of the ViewModel object?
Create a child action (Html.RenderAction) to render this data, but this requires a second set of lookups since the child action requires another full cycle of instantiating the controller.
Helper method/property called in each action method.
Thought or opinions on a best approach here?
A filter is probably your best bet and you can store the object in ViewData.
Another option (not a better one) is to create your own controller base class that overrides the ExecuteCore method and does the lookup there.
I did this for logging since I want to log each page view and I didn't want to have to add a filter to each and every controller I made. In mvc 3 there will be a way to declare global filters which can fix this as well.
Ok, so given what you've told me, I would suggest using a custom ModelBinder.
It's the best fit for the situation. I would argue that using a filter is the wrong approach because a filter's job isn't to bind data - that's a job for a ModelBinder.
HTHs,
Charles
EDIT: I've just been thinking about it and I'm a little bit torn if you should use a model binder or not.
The general rule of thumb I just came up with is that if you need the ProjectDetails inside the action itself, use a ModelBinder but if you don't need the ProjectDetails inside the action, use an ActionFilter to just add it to your model / viewdata.
Maybe someone else could throw their 2c in.
You could override the OnActionExecuting() method in your controller and get the data there.
I have a view to display a list of items.
The user can edit, delete or create new items, but according to their authorizations they may or may not be allowed to do some of this actions.
I have the requirement to display only the actions which the current user is allowed to do, but I don't want to clutter the views with authorization if-else's
Despise of being a very common requirement, I can't find a real satisfactory way of doing it.
My best approach so far is to provide an overload to the Html.ActionLink extension method that takes the permission to ask for, but there are going to be more complex scenarios, like hiding entire blocks of html or switching a textbox for a label+hidden.
Is there a better way to do this?
One example I can think of would be to invoke Html.RenderAction (link: http://msdn.microsoft.com/en-us/library/ee703490.aspx), and then pass the link you wish to use as a route value to the action method (it will appear as a parameter on your action). Because it's a RenderAction, you get to go back through the controller process and thus you can have it render whatever view or data you want depending on the user's state.
Example:
<% Html.RenderAction("Permissions" /* Controller */, "PermissionLink", new { Url = "Admin.aspx" }); %>
And your controller would have something like:
public ActionResult PermissionsLink (string url)
{
// Do Whatever kind of Authentication you want here, Session is available, etc
if(authenticated)
return View("Link");
else
return View("Blank");
}
I personally don't see anything wrong with this kind of conditional logic within the view. The logic is still all about presentation. You decide whether to show or hide, enable or disable, highlight etc. This is the view's job, not the controller's. As long as the view does not need to actually compute anything to come to its decision. The controller should be agnostic of the view's implementation as much as the other way around.
My approach would be this:
Make the controller do the actual logic of deciding the level of access that the user has
Pass this information to the view using (ie via the ViewModel) but in a way that is neutral to implementation details (ie "user is admin", "user is an author", etc)
Let the view draw itself appropriately using only the pre-compiled data that is provided by the controller.
This also has the benefit that the view itself can be removed and replaced without any effect on the controller.
We had this same issue. We ended up writing a lot of helper methods and in cases where lots of html output was required, we put them in partial views.
Would it not be simpler to create several views with various controls based on what values the user can change, then return the right view based on the user's access rights?
Views should be for presenting information only, there really shouldn't be any conditional logic contained in them, or at least a bare minimum.
I've always found when i get to the point where i'm finding it hard to grok a situation like yours, the best solution is always to go back to the controller and e-assess what i'm passing to the view in the first place.
By the time the View is called to do its job, all of the important 'decisions' should have already been made.
In complicated situations where are many conditions and rules I'm doing this that way:
ViewModel
public class ModelView
{
private IAuthorisationService { get; set; }
public bool CanShow
{
...
}
}
View:
<% if(Model.CanShow) { %>
<html>
<% } %>
What is the correct way to dynamically change the View (the view aspx) that a controller method uses versus using the standard naming convention.
I'm guessing it has something to do with the ViewResult and ViewName, but what is the correct syntax?
Update:
One thing I forgot... is there a way to do this without having the "action" or method name not be part of the resulting URL?
For example,
If I wanted to have a list of all the states in the USA.
http://localhost/list/states
(displays a simple list of state names)
And If I wanted to have a list of the 50 largest cities in the USA.
http://localhost/list/largest-cities
(displays the city and the population - two column grid)
So I'd like to be able to pull in different "formatters" depending on the list name.
Should I do that in a single action / multiple views?
Could I then use Routes to hide the View name in the URL?
What is the best way to approach this?
Just use the method that takes the name of the view to choose. Be careful, though. Most times what you probably want to do is redirect to a different action instead. Returning a different view won't change the url like redirecting will.
string name = ...figure out which view you want...
return View( name );
If you need to render a different view from a controller action dynamically, you can simply supply a value to the base.View() method (or the ViewResult constructor). The location of the view will always be (for the web forms view engine):
/Views/{Controller}/{View}.aspx
Edit: (Thanks to Ithi) It could also be in:
/Views/Shared/{View}.aspx