I get the whole idea of the fact that ViewBag is dynamic, and that new properties can be "added" to the ViewBag by using and initializing those properties for the first time without compilation issues.
However, I'm looking for a way to get all the properties that have been initialized on the ViewBag. ViewBag (according to MSDN) is declared as an object in the ControllerBase class, and there appears to be no method on how to get the properties of the object dynamically.
Perhaps reflection, but then again, I wouldn't know where to start.
The reason I want to do this is that I am converting a huge website from MVC to MVVM architecture. For that purpose I want to make tests that make sure that the ViewBag is not used anywhere, and that no properties on the ViewBag have been set after a controller's method has been run.
Where do I start?
Check ViewData - it contains everything in ViewBag in a form of a Dictionary.
Related
I am new to Razor Pages and looking for the best way to solve my problem.
Say I have an IndexModel class, that has some properties that rely on a DB context that is injected via the Constructer, such as a drop down list of Membership Levels, that comes directly from a table...
My question is what is the best way to handle populating this drop down list that I have for ALL requests that results in the same page being reloaded / returned. I know that I can put logic in OnGet to set up the list, the problem arises if say in OnPost, ModelState.IsValid is false, and so the page is returned with Page(). If I don't explicitly reinitialize the select list in OnPost, then I get a null reference exception, which is fair enough. Rewriting the code in the OnPost method goes against DRY principles, so I looked to writing a ConfirgureProperties() method in the class when needed.
Then by testing, I found that I can just set up a constructer that will take care of populating properties for me whenever they are needed, and I don't have to call anything else. Even when DI is involved, the injection is resolved at the top of the constructer, then I can use the context to do what I need for the other properties later in the constructer. I have seen no examples of this anywhere online, I only ever see people using constructers in page models that handle DI EXCLUSIVELY.
Is there a reason I SHOULD NOT be doing this, like bad coding practice or something, or is it ok for me to use page model constructers in this way?
Thanks
You only need to make the database call to repopulate the options in OnPost if ModelState is invalid. Chances are, if you have set up your validation correctly, that 99% of the time validation errors will be caught on the client and you won't need to repopulate the options.
Obtaining data from a database is costly, and you should only do it when necessary. So using the constructor approach contravenes this principal.
It's not like you are saving a lot of code either. Your ConfigureProperties method will only be called in two places in the PageModel.
I've inherited a code base written in ASP.Net MVC 4. Every post method takes a FormCollection. Aside from annoyance of having to access the values through quoted strings, it also leads to drawbacks such as not being able to use things like ModelState.IsValid, or [AllowHtml] attributes on my ViewModel properties. They actually did create ViewModel classes for each of their views, (though they are pretty much just direct wrappers around the actual Entity Framework Model classes), but they are only used for the GET methods.
Is there anything I'm missing about FormCollection that gives a reason why this may have actually been a good idea? It seems to only have drawbacks. I'd like to go through and "fix" it by using ViewModels instead. This would take a good bit of work because the ViewModels have properties that are interfaces and not concrete classes, which means either writing a custom binder or changing the ViewModels.
But perhaps there's something I'm missing where it makes sense to use FormCollection?
Is there any good reason to use FormCollection instead of ViewModel?
No. I have following issues.
Issue - 1
In case FormCollection is being used...It will be mandatory to Type Cast the Primitive Type Values un-necessarily because while getting the entry of specific Index of the System.Collections.Specialized.NameValueCollection, value being returned is of type String. This situation will not come in case of Strongly Typed View-Models.
Issue - 2
When you submit the form and goes to Post Action Method, and View-Model as Parameter exists in the Action method, you have the provision to send back the Posted Values to you View. Otherwise, write the code again to send back via TempData/ViewData/ViewBag
View-Models are normal classes, created to bind data to-from Views
Issue - 3
We have Data Annotations that can be implemented in View Model or Custom Validations.
ASP.Net MVC simplifies model validatons using Data Annotation. Data Annotations are attributes thyat are applied over properties. We can create custom validation Attribute by inheriting the built-in Validation Attribute class.
Issue - 4
Example you have the following HTML
<input type="text" name="textBox1" value="harsha" customAttr1 = "MyValue" />
Question : How can we access the value of customAttr1 from the above eg from inside the controller
Answer : When a form get posted only the name and value of elements are posted back to the server.
Alternatives : Use a bit of jQuery to get the custom attribute values, and post that along with the form values to action method
Another option is to rather put what you got in your custom attributes in hidden controls
That's the reason, I would always prefer to use View-Models
The only advantage I can think of is if you want to use the automatically generated controller provided when you don't specify a EF model to be strongly typed to. In that case, your Create and Edit actions will use the FormCollection object as it is a reliable, pre-existing artifact of the framework to work with for this purpose. Perhaps the previous developer chose this option while creating his controllers, and stuck with it since Visual Studio must know what it's doing :)
But, in reality, I would never recommend this headstart of a few seconds. It's always better to build out viewmodels, I would recommend looking at the effort to move in that direction if only for maintenance purposes. With model binding and strongly typed views and html helpers, you are much more likely to reduce the number of run-time errors as a result of changing some magic string and not realizing it until your page blows up.
Ok, I see the general consensus here is that it isn't liked. To offer another perspective, I've always liked using the formcollection passed into the controller on POST actions. It offers the use of the TryUpdateModel method from the controller which will map the collection to your strongly typed class. TryUpdateModel also has overloads that allow you to white list the properties of the model that you want to allow to be updated.
if (TryUpdateModel(viewModel, new string[] { "Name" }))
{
//Do something
}
It still allows all the model binding you want, but helps to keep anything other than the "Name" property on my viewmodel from being updated.
You can see more about the TryUpdateModel method here:
http://msdn.microsoft.com/en-us/library/system.web.mvc.controller.tryupdatemodel(v=vs.108).aspx
There are always workarounds for getting away from a FormCollection lol.. you can have hidden fields bound to your view model variables in the form to your heart's content.
Form collections mostly emerge from the laziness of creating a view model but still end up taking time trying to get figure out how to get the values out of it in your controller :P
I think it was simply created in the very beginning of MVC as an alternative to using strongly typed views when having very simple forms - back in the days when everyone used ViewBag :) ... and once hey had it in there they couldn't just take it out as simple as that.
Maybe you can use it if you are absolutely sure your view will never have more than one form input? Probably still a bad idea though..
I cant find any recent articles talking about any advantages of form collections.. while strongly typed views are everywhere.
Yes. Sometimes, it can be useful. Here's an example:
Let's say we have in our db "date_and_time_field".
In Razor View, we want to use two form fields. The first one "Date" (maybe with jQuery UI Datepicker). The second one "Hour".
In the Controller Action, we compose the "date_and_time_field" by means of Request.Form["Date"] and Request.Form["Hour"].
There are other scenarios where it can be useful:
A cross-table (with checkBoxes in Razor view)
The collection Request.Unvalidated().Form (maybe this is not part of your question: I don't wanna be off-topic)
The default model binder will do almost everything you need it to do. I resorted to the FormCollection once - only to later figure out how to bind arrays of elements into a collection on the ViewModel.
Just go ViewModel. Better all around, for every reason enumerated.
With form collection you will be able to get all the values inside the form. There can be situations where you may need to pass some additional values from the form which may not be part of your view model.
Just take an example of passing 10 hidden values from the form. The form collection makes sense.
The only difficulty that you may face is type casting. All form collection items that you get will be string; you may need to type cast based on your requirement.
Also model state validation is another area where you may face a challenge.
You can always add the form collection properties to your method signatures. They will automatically be populated by form values with corresponding keys.
Well with Forms Collection you will find a quick way to get the values of a form. Otherwise you have to create a class that mimics the Form Fields and people are sometime lazy to create custom classes for less important/rarely used Forms.
No there is no extra benefit (in fact limited) of forms collection over a custom class as action parameters and it should be avoided whenever possible.
Responding to the title question: yes.
There are some situations that FormCollection needs to be used. For instance, suppose a ViewModel that has a property that implements the 1 to N relation (in concrete case, a TimesheetViewModel with ICollection<TimesheetEntryViewModel>), and the Controller has to perform a validation between the time entries to not get a time collision between the end time of an entry and the start time of the following entry. To mark a related entry with a validation error, how can be the line index be retrieved?
Well, with the default model binding, the index value is lost in the Controller logic. Fortunately, FormController stores the index you used in the View and a more specific validation can be done.
There are type of SPA apps where you have no idea about your model (there is no ViewModel at all and views are created dynamically (for short ;))), so FormCollection is your only choice where you implement custom post validation having entire page input values...
If your view has a knowledge about the model then, of course, you can use your concrete ViewModel object. That's easy ;)
In my views I set the Title using the common ViewBag approach. I set the value on the ViewBag in the view and not in the controller.
The code in the view is run after all four virtual methods in a class that derives from ActionFilterAttribute. Thus, when I try to read the title from the ViewBag it has not been set yet. Conversely, any value I set inside one of those methods is at risk of being overwritten later.
I'd prefer not to move these lines into the controllers, mainly because that would require me to edit a large number of views and controllers.
Is there any alternative?
I can't pass the value to the Attribute constructor as a parameter because it is not a constant.
We have a model (say, List<string>). The function that builds the list is non-deterministic and the output is needed to be referenced in both controller and the view during the lifetime of the request. Since it's per-request, it cannot be static or singleton.
It's a common structure and it can be referenced from any view or controller.
Since we can't access controller from the view (by principle, and we agree), we cannot keep it in the controller. We're currently keeping it in the ViewData dictionary and initialize it in the controller, or the view (if the controller didn't need it).
We think that using ViewData for this purpose may not be ideal since it's not created to be consumed by a controller in the first place. Is there a better way to share common per-request data between Controller and the View? If not we'll stick with ViewData.
There is HttpContext.Items dictionary but I'm not sure if it fits to this purpose.
the output is needed to be referenced in both controller and the view during the lifetime of the request
The way MVC works, the Action code in the Controller is executed, and the resulting data is passed to the view engine that draws the page using the info you passed either with the call to View(data) or in the ViewData dictionary.
I don't know what you are trying to do, but it sounds like it's more a problem of a bad approach than a technical one (I might be wrong, though).
Could you explain why you need the controller while the View is rendered? If you need any logic associated with the List (to process it or do anything with it) I would just create a new class that extends List<T>, add the logic to that class instead of the controller, and pass an object of that class to the View, either using View() or ViewData[].
What is exact thing you're trying to do?
Seems like you just asking about the way to pass some data from the Controller to the View which is rather trivial task. Just use ViewData, yes, or ViewBag in MVC3 case or use ViewModels.
Or there is somewhat special case? What does "referencing from Controller and from View" mean? Where the data is coming from? Usually the case is that Controller prepares data for the View and passes it as an ActionResult (or better, as a ViewModel). View should never take some data on its own bypassing the controller.
Controller action should always be called be first. If you have multiple controllers calling the same view/partial view then you should be refactoring the code to one method and call that.
ViewData is the solution to do this, if your really wanting "once access" type information then maybe TempData but ViewData is designed for this.
All my controllers are based off of a BaseController, to share properties between them and override OnActionExecuting to set some values based on the route.
I'm creating a BaseViewData class to do the same for all my view data.
At the moment I'm populating the view data like so (C#):
var viewData = new BaseViewData
{
Name = "someName",
Language = "aLanguage",
Category = "aCategoryName"
};
I do this in every action that requires the view data. Some of the properties are common, need to be set throughout every action. Is there a way to set some of the properties on a more global scale?
If I instantiate the BaseViewData class in the OnActionExecuting method on the BaseController, how do I access the BaseViewData properties from the action in the regular controllers (derived from the BaseController)?
Update in response to Dennis Palmer:
I'm essentially doing this because of a nagging issue I'm having with ViewData["lang"] not being populated randomly on some requests. ViewData["lang"] contains "en" if the language is English, and "ja" if it is Japanese (well, it's supposed to anyway). I populate ViewData["lang"] inside OnActionExecuting on the BaseController.
In my view, I make a call to some partial views based on the language:
<% Html.RenderPartial(ViewData["lang"] + "/SiteMenu"); %>
But I'm randomly getting errors thrown that state "Cannot find /SiteMenu", which points to the fact that ViewData["lang"] has no value. I just cannot find any reason why ViewData["lang"] would not get populated. So, I'm rewriting the site to use ONLY strongly typed view data (and setting some hard defaults). But if another method is better, I'll go that way.
Thank you!
I'm not sure I follow exactly what you're trying to do, but if your view is using values in the route to display certain information, it seems like adding your own extension methods for HtmlHelper would be a better way to go.
Are Name, Language and Category contained in your routes? If so, then HtmlHelper will have access to the route info and can determine what to display via the extension methods. What is the correlation between your routes and what your views need to know?
Update: Is lang part of your route? If so, then I would still contend that you could write an HtmlHelper extension method that looks at the route data directly and determines which partial view to render. That way your controller wouldn't even need to worry about setting the ViewData["lang"]. The view would always know how to render based on the route.
Update 2: I think dismissing use of an HtmlHelper extension method because it re-evaluates the route data might be a case of premature optimization. Your controller inheritance scheme sounds overly complex and you asked the question because the way you were setting ViewData was unreliable. I doubt that pulling the value from route data would be much, if any, less efficient than setting and reading from ViewData.
From your comment:
In the controller I use the lang value
to determine which view to show as
well.
That only makes me think that there are more pieces of your system that I'd need to see in order to give better advice. If you have separate views for each language then why does the view need to be told which language to use?
Another alternative to consider would be using nested master pages. You could have a single master page for your site layout and then a nested master page for each language that just contains a hard coded lang value.
Perhaps instead of this inheritance scheme you have, you can just use action filters to add the data you need.