I am confused about how model and view can interact
I was making a simple to do app with mvc pattern and I saw an article which said you shouldn't pass the model values directly to the view, which made the project more complex than I thought (I am relatively new to programming and this is the first time I am trying out a design pattern).
But then later on I talked to someone who said that that is not true and you can send the model data directly to view, he didn't even use classes or some kind of grouping to separate the function he just put them in separate files.
I was wondering if there is a guideline that I couldn't find or we can do whatever we want as long as they are kind of separated. I would love an article or a guide to read up on as well.
Since, I am not 100% sure the context in which you are trying to apply the MVC pattern, a good generic explanation of MVC can be found in GoF's 1995 book, Design Patterns: Elements of Reusable Object Oriented Software.
In the book, they state the following.
The Model is the application object, the View is its screen
presentation, and the Controller defines the way the user interface
reacts to user input.
A more robust explanation can be found from Martin Fowler where he also
makes the case for a variation of Model View Controller that uses a Presentation Model.
If you are referring to Spring MVC then there is some magic that blurs the lines a bit. But in general, you have a controller that represents some screen or an encapsulated piece of functionality that the user (web requests) interact with. The controller serves up responses that are derived from the domain, usually via a Spring Service (i.e. #Service). The domain (Model) doesn't know anything about the View and the View may or may not know anything about the domain.
Given that, the View should be derived from the Model. But that's not always the case since sometimes how we present things to a screen is not the best logical way to model things in our domain - not to mention, the domain should be presentation agnostic. This leads into Fowler's argument for a Presentation Model, which is a model that belongs to the Presentation.
I call this a Presentation Model because it's a model that is really
designed for and thus part of the presentation layer.
Microsoft took that idea and ran with it in a variant of MVC called MVVM (Model View ViewModel).
You can read more about that in Microsoft's documentation on ASP.Net Core.
So, back to your original question of "Should you pass the model directly to the view?" If you are using MVC then the controller is what provides the interaction. But if you're really asking, "Can you bind your view directly to the model?" If your model has all the stuff you need organized how your view needs it, then sure. And if it's simple enough, maybe that's the way to go. Otherwise, you could go with something like a Presentation Model or MVVM.
Related
Once again, an MVC-related question. A few days ago I started reading the Cocoa Fundamentals Guide from Apple in which Apple explains their implementation of MVC.
In the chapter MVC as a Compound Design Pattern (link), they compare two MVC-versions:
The old / traditional SmallTalk version:
The current Apple-defined version:
They describe this current model as follows:
The controller object in this compound design pattern incorporates the
Mediator pattern as well as the Strategy pattern; it mediates the flow
of data between model and view objects in both directions. Changes in
model state are communicated to view objects through the controller
objects of an application.
The traditional pattern looks like MVC, nothing wrong. But the name of their current pattern confuses me. In my knowledge this could be seen as plain MVP because the Controller always seems to mediate between View and Model.
Am I completely wrong, do I misunderstand MVC or MVP? Or did Apple just use the wrong name for this pattern? And more importantly, WHY is this current pattern called MVC?
You're not wrong, but nor is the author of the Apple documentation.
The history of MVC is now long and complex -- not least because many systems advocated a tripartite separation which actually muddling the controller into the model or mixing the controller into the view. From the very early Smalltalk implementations, it became clear that keeping model information out of the view was a very good thing, and that this was fairly easy to do.
Cleanly separating the responsibilities of the controller and the view, on the other hand, is much less straightforward. Lots of views want to be reused, like buttons or textfields. The reusable part of their controllers wants to be reused too. But you don't PUSH a textfield or BOLD a button; lots of the button behavior is tied pretty closely to the view. At the same time, it can be hard to be sure when a business rule belongs in the model and when it belongs in the controller.
In addition, this (very good) Apple document is trying to capture a philosophical design idea, not describing The One True Way. Lots of Cocoa controllers subsystems look a lot like traditional MVC. Traditional cocoa deemphasized controllers, so this document is, in essence, arguing to give them a place as mediators between (reusable) views and (potentially reusable) models.
Lots of Cocoa implementors prefer thin controllers, essentially working as façades to decouple view and model.
Since MVP is a subset of MVC it's not surprising to find it in MVC systems. Yes, that second diagram illustrates the MVP pattern.
Apple calls it a mediating controller which – I synthesize – is just another name for MVP.
Frankly I'm not sure the term MVP ought to catch on. It implies it's a totally different pattern, and presenter seems focused on the UI, when sometimes it's just a relationship between model and controller. Mediating controller describes the distinction quite simply.
I had to look up MVP even to know what the heck you were asking about. The term was used in a paper in 1996. When OS X was released it would still have been new.
While using a custom MVC framework I found that the view can actually access data in the model. That was a bit of a surprise because I always thought the V must go through the C. It was something like
//this is completely made up but not far off
serverside foreach(var v in Model.GetSomeList()) {
<div>#v.name</div>
}
Do many MVC frameworks in any programming language allow the view to access anything in the model? When do i choose what should go through the controller and what is ok to access from the view?
Usually that "Model" is really like viewmodel, not the business layer Model object, although it could be the POCO version of the business object. Basically, the view is bound to some poco without any business logic.
Information flow in classical MVC.
Data in MVC should not go from model through controller to view. That is violation of the original concept.
If you read the original definition of MVC design pattern you will notice that Views are meant to request the data from Model. And views know when to do it, because they are observing Model for changes.
Modern interpretations.
In the original concept you were meant to have small MVC triad for each element in the application. In modern interpretation (as per Martin Fowler), the model is not anymore any single object or class. Model is a layer, which contains several groups of objects. Each with a different set of responsibilities.
Also, with the rise of Web there was another problem. You cannot use classical MVC for websites. Theoretically now you could achieve it by keeping an open socket and pushing a notification to the browser every time you changed something in the model layer.
But in practice even a site with 100 concurrent users will start having problems. And you would not use MVC for making just a blog. Using such an approach for even minor social network would be impossible.
And that was not the only divergence from the original concept.
MVC-inspired patterns
Currently, along with classical MVC (which is not even all so classical anymore). There are three major MVC inspired patterns:
Model2 MVC
This is basically same classical MVC patter, but there is not observer relationship between model later and view(s). This pattern is meant to me more web-oriented. Each time you receive a user request, you know that something is gonna change in model layer. Therefore each user request cause view instance to request information from the model layer.
MVP
This pattern, instead replaces controller with a presenter. The presenter request data from model layer and passes it to current view. You can find patterns definition here. It is actually a lot more complex, and I, honestly, do not fully understand it.
In this case the View is passive and will not request any data from model layer.
MVVM
This pattern is closer to MVP hen to classical MVC. In this case the controller-like structure (which actually would be more then a monolith class) request data from model layer and then alters it in such a way as it is expected by the (passive) view.
This pattern is mostly aimed at situation where developer does not have full controller over views or/and model layer. For example, when you are developing some application where model layer is SAP. Or when you have to work with an existing frontend infrastructure.
FYI: what is called "MVVM" in ASP.NET MVC is actually a good Model2 implementation .. what they call "viewmodels" are actually view instances and "views" are just templates that are used by views.
This is common. If you look at the Wikipedia page for MVC, this is what it says for the view:
A view requests from the model the information that it needs to generate an output representation.
MVC is an architectural style, so some people change it as they see fit. From the design intentions of the architecture this particular question is certainly not frowned upon.
Data binding establishes a direct coupling between the view and the model, thereby bypassing the controller. Fundamentally this breaks with the Model-View Controller architectural pattern, am I right in thinking this? Does this make data binding a "bad thing"?
Edit: As example, angular claims to be a MVC framework, yet one of its main features is data binding.
In my opinion Data Binding can be a valid implementation of the MVC Pattern since the data binding mechanism itself acts as the controller in that case.
For example in the mentioned angular it seems like the $watch function is a shortcut to implement features that are typical Controller responsibilities and features in an MVC-style way.
So in my opinion data binding is an evolution step that implements best practices learned by implementing classic MVC controllers.
UPDATE
But in original pattern sense I would characterize data binding more like MVP or Passive View.
But the differences aren't that sharp in my opinion since it always also depends on your UI technology.
Not necessarily, since you don't have to bind your Model objects to the view.
What I usually do is create simple DTOs (or Presentation Objects) that contain only the data I want to display, and that's what the View layer displays.
In that case, the Controller retains its function as a translator between actions performed on the DTOs and actions on the underlying Model entities.
Actually, when your data is abstracted properly, the act of pushing the content of your models to your UI is a repetitive task that normally lead to some kind of "helpers".
Let's say to push a list of items to a combobox. This is not necessarily part of the controller as you may want to share such functionality. Also pushing the value of the control (to keep it simple, let's say the text of a textbox) is repetitive and bi-directional.
Also here you repeat your self (think of DRY) and do the same thing over and
over again.
That's exactly the point where databinding comes into play. This can take over the tasks that anyway are identical for simple controls (checkbox, textbox, combobox). For grid control and the like it may be specific.
Have a look at mvc & databinding: what's the best approach?. Here I discuss what could be the optimum when using databinding in combination with MVC.
Data Binding does not directly couple the view and model, so it is not a Bad Thing®. It is an integral feature of the MVC architecture, which the GoF Design Patterns book describes succinctly in chapter 1.
MVC decouples views and models by establishing a subscribe/notify protocol between them. A view must ensure that its appearance reflects the state of the model. Whenever the model's data changes, the model notifies views that depend on it. In response, each view gets an opportunity to update itself. This approach lets you attach multiple views to a model to provide different presentations. You can also create new views for a model without rewriting it.
It's a common misconception that MVC is a layered (3-tier) architecture. It is not. The model updates the view(s) directly. But this does not mean the two are coupled! A publish/subscribe design keeps the model and view decoupled.
This more general design is described by the Observer design pattern.
I was originally going to make this a longer question, but I feel like the shorter I make it, the better you'll understand what I mean.
The MVC architectural pattern has 3 dependencies. The View depends on the model. The Controller depends on the View and Model. The Model is independent.
The Layers architectural pattern defines N - 1 dependencies, where N is the number of Layers.
Given three Layers: Model, View, and Controller, there are only 2 dependencies, as opposed to 3 with traditional MVC. The structure looks like this:
View ---> Controller ---> Model
[View depends on Controller, Controller depends on Model]
It seems to me that this style accomplishes the same goals and produces looser coupling. Why isn't this style more common? Does it truly accomplish the same goals?
Edit: Not ASP.NET MVC, just the pattern.
With regard to griegs's post:
As far as mocking, Layers still allows you to use the Command Processor pattern to simulate button clicks, as well as any other range of events.
UI changes are still very easy, perhaps even easier. In MVC, the Controller and View tend to mesh together. Layers creates a strict separation. Both Layers are black boxes, free to vary independently in implementation.
The Controller has 0 dependencies on the View. The View can be written, and time can still be saved with loose coupling.
Because you decouple the interface from the controller making changes easier.
Also consider the scenario where you need to get started on a project but the artwork won't be ready for weeks or months. Do you wait or do you write all the code required for the pages and simply then wire up the view to the controller.
At least that's what we did and we saved months.
Also it made UI changes easier to cope with because there wasn't any code in our aspx pages that did anything.
Our tests were also better as we could mock up anything including button clicks etc.
And if you're talking about the asp.net-mvc framework, there is no code in the aspx files and no viewstate etc.
In proper MVC the controller doesn't depend on the view afaik. Or maybe I'm not understanding it correctly.
The model defines the data.
The view defines what the output looks like.
And the controller is a translator from a model-understood grammar to view-understood grammar.
So essentially the controller is independent. The view is independent. And the model is independent.
Yes? No?
I'll be bold, and try to explain why your method didn't catch on.
The MVC pattern basically requires the view and model layers to agree on an API.
Since one serves the other and there are no dependencies inside the code it leaves the controller to behave generically, all it needs to do is take a certain structure in the view layer and call the matching API on the model layer.
You'll note that agreeing on an API between the view and model isn't really such a big deal it has to happen anyway. And what you get is good separation between back-end front-end development.
In your proposed solution a lot of development is required on the controller side. The controller will be required to understand all the elements in the view and to map them to the specific calls required on the model layer.
Since the controller is a single access point connecting many views to many models this can quickly get out of hand and end up being an incomprehensible controller module.
Look at some Struts2 examples to see what I mean...
I think I'm understanding your point:
Yes you can make the View only depend on the Controller only by making the Controller transform (using PHP as an example) the Model objects to non-Model objects like simple arrays.
As we already know, performing this transformation can be more effort than it's worth if the decoupling isn't actually needed. If the View uses the Model objects then it has this dependency. However, this can be relieved a bit by having the View depend solely on the Controller for its required input, which can be Model objects.
The Symfony PHP framework promotes this style of skinny controller shuffling between Model and View. You can still directly call upon the Model layer to retrieve objects within the View layer but it's strongly urged against for the coupling issues you bring up. Within the View you can call include_component() which actually goes back up to the Controller if you need to query the Model.
I haven't gotten back to this in a long time, mostly because I was still thinking. I was unsatisfied with the answers I received, they didn't really answer my question.
A professor, recently, did steer me in the right direction. Essentially, he told me this: Layers which separate Model, View, and Controller is MVC. In the vanilla MVC architectural pattern, the dependency between the View to the Model is often not used, and you effectively end up with Layers. The idea is the same, the naming is just poor.
Choosing a presentation pattern for a new or enterprise web development on the Microsoft platform is a daunting task, in my opinion there are only three; View Model, Model-View-Presenter (MVP) or ASP.NET MVC (a Model2 derivative).
You can read the full article here ASP.NET MVC Patterns
I'd like to add some more things. First of all for my point of view is we use the model as container for the information we want to pass and show on the view. Usually the action method into the controller ends with return view("viewName",model).The view itself probabily will change its layour against the model :
on the view :
if(model.something==true) {
%>
somethign to show
<%
}
At this poinf the definition of model is hard to find.
I can say (especially on enterprise conext) the are two "model"
one is the domain model/entity model or how you want to call it that wraps the data coming from the lower layers (database,etc) and the view-model who contain the information we wants to show plus any other information we need to hide/show portion of interface
The controller orchestrate the the views and is indipendent from the view but a bit dipendent from the model:
into the controller
pulic actionResult Index(){
....
if(model.BoolProperty==true){
return ("firstView);
}
else
{
return ("secondView");
}
}
I hope it makes sense
In my opinion ,you'd better try it in your programme , you can use ruby on rails ,or codeigniter( for php ),these great framework may be helpful to your understanding the MVC.
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I've heard the term MVC (Model View Controller) tossed about with a ton of Buzz lately, but what really is it?
You might want to take a look at what Martin Fowler has to say about MVC, MVP and UI architectures in general at Martin Fowlers site.
I like this article by Martin Fowler. You'll see that MVC is actually more or less dead, strictly speaking, in its original domain of rich UI programming. The distinction between View and Controller doesn't apply to most modern UI toolkits.
The term seems to have found new life in web programming circles recently. I'm not sure whether that's truly MVC though, or just re-using the name for some closely related but subtly different ideas.
MVC is a design pattern originally pioneered in the olden days of smalltalk.
The concept was that a model would represent your application state and logic, and controllers would handle IO between "Views".
A View was a representation of the state in the model. For example, your model may be a spreadsheet document, and you may have a view that represents it as a spreadsheet and a view that represents it as a pivot table.
Modern MVC has been polluted with fake MVC web junk, so I'll let others answer that.
Here is a naive description of MVC : http://www.devcodenote.com/2015/04/mvc-model-view-controller.html
A snippet:
Definition : It is a design pattern which separates an application into multiple layers of functionality.
The layers:
Model
Represents data.
It acts as an interface between the database and the application (as a data object).
It will handle validations, associations, transactions etc.
Controller
It gathers and processes data.
Handles code which does data selection and data messaging.
View
Displays output to the users.
MVC Design Pattern:
4 parts = User, View, Controller, Model.
User:
- sees the View and uses the Controller.
Model:
- holds the data and updates the Model that there is new data/state.
View:
- displays the data that the Model has.
Controller:
- takes the request from the user to get or set information, then communicates with either the View or Model, resp.
- it "gets" via the View.
- it "sets" via the Model.
As the tag on your question states its a design pattern. But that probably doesn't help you. Basically what it is, is a way to organize your code into logical groupings that keep the various pieces separate and easily modifiable.
Simplification:
Model = Data structure / Business Logic
View = Output layer (i.e HTML code)
Controller = Message transfer layer
So when people talk about MVC what they are talking about is dividing up there code into these logical groups to keep it clean and structured, and hopefully loosely coupled. By following this design pattern you should be able to build applications that could have there View completely changed into something else without ever having to touch your controller or model (i.e. switching from HTML to RSS).
There are tons and tons of tutorials out there just google for it and I'm sure you'll turn up at least one that will explain it in terms that click with you.
Wikipedia seems to describe it best so far:
http://en.wikipedia.org/wiki/Model-view-controller
Model-view-controller (MVC) is an architectural pattern used in software engineering. Successful use of the pattern isolates business logic from user interface considerations, resulting in an application where it is easier to modify either the visual appearance of the application or the underlying business rules without affecting the other. In MVC, the model represents the information (the data) of the application and the business rules used to manipulate the data; the view corresponds to elements of the user interface such as text, checkbox items, and so forth; and the controller manages details involving the communication to the model of user actions such as keystrokes and mouse movements
The MVC or Model-View-Controller User Interface Paradigm was first described by Trygve Reenskaug of the Xerox PARC. In first appeared in print in Byte magazine volume 6, number 8, in August of 1981.
This What is MVC blog article on Oreilly has you covered.
MVC is a software architecture pattern that separates representation from user interaction.
Generally, the model consists of application data and functions that interact with it, while the view presents this data to the user; the controller mediates between the two.
It is a way of separating the underlying functionality of your application (model) from the way it interacts with the user (view). The controller coordinates how the model and view talk to each other.
Whilst it is all the rage at the moment, it is important to remember that preventing the model itself being able to determine exactly how its data is presented to the user can seen as a negative thing. The most obvious example is with HTML. The original intention of HTML was that there should be a clear separation of the model (HTML) from the view (rendered webpage) via a controller (the browser). There has been such a backlash against this original intention that browsers are criticised if they do not render a page pixel perfect to the designer's desired view.
MVC is a way to partition a user interface element into 3 distinct concepts. The model is the data on which the interface operates. The view is how the element is represented visually (or maybe audibly?). The controller is the logic that operates on the data.
For example, if you have some text you want to manipulate in a UI. A simple string could represent the data. The view could be a text field. The controller is the logic that translates input from the user - say character or mouse input - and makes changes to the underlying data model.
Like many have said already, MVC is a design pattern. I'm teaching one of my coworkers now and have explained it this way:
Models - The data access layer. This can be direct data access, web services, etc
Views - The presentation layer of your application.
Controllers - This is the business logic for your application.
This pattern enhances test-driven development.