Model-View-Presenter
In MVP, the Presenter contains the UI business logic for the View. All invocations from the View delegate directly to Presenter. The Presenter is also decoupled directly from the View and talks to it through an interface. This is to allow mocking of the View in a unit test. One common attribute of MVP is that there has to be a lot of two-way dispatching. For example, when someone clicks the "Save" button, the event handler delegates to the Presenter's "OnSave" method. Once the save is completed, the Presenter will then call back the View through its interface so that the View can display that the save has completed.MVP tends to be a very natural pattern for achieving separated presentation in Web Forms. The reason is that the View is always created first by the ASP.NET runtime. You can find out more about both variants.
Two primary variations
Passive View: The View is as dumb as possible and contains almost zero logic. The Presenter is a middle man that talks to the View and the Model. The View and Model are completely shielded from one another. The Model may raise events, but the Presenter subscribes to them for updating the View. In Passive View there is no direct data binding, instead the View exposes setter properties which the Presenter uses to set the data. All state is managed in the Presenter and not the View.- Pro: maximum testability surface; clean separation of the View and Model
- Con: more work (for example all the setter properties) as you are doing all the data binding yourself.
- Pro: by leveraging databinding the amount of code is reduced.
- Con: there's less testable surface (because of data binding), and there's less encapsulation in the View since it talks directly to the Model.
Model-View-Controller
In the MVC, the Controller is responsible for
determining which View is displayed in response to any action including
when the application loads. This differs from MVP where actions route
through the View to the Presenter. In MVC, every action in the View
correlates with a call to a Controller along with an action. In the web
each action involves a call to a URL on the other side of which there is
a Controller who responds. Once that Controller has completed its
processing, it will return the correct View. The sequence continues in
that manner throughout the life of the application:
Action in the View
-> Call to Controller
-> Controller Logic
-> Controller returns the View.
One other big difference about MVC is that the View does not directly
bind to the Model. The view simply renders, and is completely stateless.
In implementations of MVC the View usually will not have any logic in
the code behind. This is contrary to MVP where it is absolutely
necessary as if the View does not delegate to the Presenter, it will
never get called.Presentation Model
One other pattern to look at is the Presentation Model pattern. In this pattern there is no Presenter. Instead the View binds directly to a Presentation Model. The Presentation Model is a Model crafted specifically for the View. This means this Model can expose properties that one would never put on a domain model as it would be a violation of separation-of-concerns. In this case, the Presentation Model binds to the domain model, and may subscribe to events coming from that Model. The View then subscribes to events coming from the Presentation Model and updates itself accordingly. The Presentation Model can expose commands which the view uses for invoking actions. The advantage of this approach is that you can essentially remove the code-behind altogether as the PM completely encapsulates all of the behaviour for the view. This pattern is a very strong candidate for use in WPF applications and is also called Model-View-ViewModel.There is a MSDN article about the Presentation Model and a section in the Composite Application Guidance for WPF (former Prism) about Separated Presentation Patterns
To figure out the difference let’s have a look at the conditions why MVC has been widely spread out and what benefits it’s provided for application development.
Let’s come back to the past. At the times when AJAX statement still had been unknown. At the times when programmers were afraid of using JavaScript in browser and that’s why had to reload the whole page.
Let’s take a simple example. A user fills out the registration form and sends it to the server. Server validates entered data, determines the errors and sends the form with the filled data back to the user.
Sending data to the server, in fact, we send the event with the data to the particular controller. It performs some actions with the data and transfers the control to the View. View generates the result with the HTML and sends it back to the user.
What happens? Apparently the whole browser page and its server representation are the one big and distributed visual component. It has events as well as interface and implementation.
MVC is advantageous to use when components are redrawn on every event received from the user.
MVP was invented on a bit different conditions - when you build the application based on component framework and there is no need to constantly recreate the View.
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