You are going to transition the Umbrella app to an MVP architecture. One popular way of managing the parts of an app is to organize them by feature. A feature is composed of the model , the views , the presenters , as well as dependency injection DI code to create and provide each component. This way, you can add and remove features from your app as a module. Your app has only one feature: the main screen.
You are going to implement MVP for the main screen, and you will create some components prefixed with Main. To start, create an interface named DependencyInjector in the root com. Next, create a class DependencyInjectorImpl in the same package that implements the interface. We also have interfaces to define the presenter and the view.
Interfaces help with decoupling the parts of the app. First, create a new file named BasePresenter. This is a generic interface that any presenter you add to your project should implement. It contains a single method named onDestroy that basically acts as a facade for the Android lifecycle callback.
Similar to BasePresenter , this is the interface that all views in your app should implement. Since all views interact with a presenter, the view is given a generic type T for the presenter, and they must all contain a setPresenter method. Next, create a contract interface named MainContract , which defines interfaces for the view and presenter for the Main screen, and update it to look as follows:.
You can see that MainContract. Presenter is interested in being called back by the MainContract. Similarly, the view can be invoked to display weather information through displayWeatherState , which is only called by the presenter. You have your interfaces in place. First, create a new file named MainPresenter.
Here, you do some clean up in onDestroy and invoke fetching the weather data in both onViewCreated and onLoadWeatherTapped. An important point to notice is that the presenter has no code that uses the Android APIs. To start, add Mockito to your testing dependencies in the app module build.
If you want a deep dive into the framework, check out our tutorial all about it. There is an empty unit test file in the test package named MainPresenterTest. Update the contents of the file to be as follows:. You added the mocking, stubbing, setup and tear down code you need to run the one test. As the test illustrates, you can mock the view interface which in the app is implemented by MainActivity and test your business logic with a simple unit test.
The presenter is absent of Android framework components, and thus you can test it using lightweight unit tests rather than instrumented UI tests. The business logic in Umbrella, i. Thus, it is really important to add tests to this logic, and unit tests are easy and fast to write and run.
Note, the final project also contains an instrumented test file named MainActivityTest. With an instrumented UI test, you can also test your view components, but they must be run on an Android emulator or device, and so do not run as fast as unit tests. At any given time, the activity and any associated fragments the views may be destroyed. Since the presenter keeps a reference to the view, you may try to update an activity that is already detached. In your sample app, you added a method named onDestroy to BasePresenter.
When the activity lifecycle method onDestroy gets called on MainActivity , you call MainPresenter::onDestroy , which sets the presenter reference to view to null. Kotlin null safety features prevent you from calling a method on a null view. Most of the logic will exist in the presenters of your app. Click here to head to a guide uniquely curated by our experts with the aim to make you industry ready in no time!
Most of the core business logic resides in Controller. During the lifetime of an application, this file grows bigger and it becomes difficult to maintain the code. Because of tightly-coupled UI and data access mechanisms, both Controller and View layer falls in the same activity or fragment.
This cause problem in making changes in the features of the application. It becomes hard to carry out Unit testing of the different layer as most of the part which are under testing needs Android SDK components. MVP pattern overcomes these challenges of MVC and provides an easy way to structure the project codes. The reason why MVP is widely accepted is that it provides modularity, testability, and a more clean and maintainable codebase.
It is composed of the following three components: Model: Layer for storing data. It is responsible for handling the domain logic real-world business rules and communication with the database and network layers.
View: UI User Interface layer. Presenter: Fetch the data from the model and applies the UI logic to decide what to display. The view will sometimes interact with the presenter, usually through some interface. This comes down to implementation; do you want the view to call methods on the presenter or do you want the view to have events the presenter listens to? It boils down to this: The view knows about the presenter. The view delegates to the presenter.
The controller then creates the appropriate view and interacts with the model to further configure the view. It boils down to: the controller creates and manages the view; the view is slave to the controller. The view does not know about the controller. The input is directed at the Controller first, not the view. That input might be coming from a user interacting with a page, but it could also be from simply entering a specific url into a browser.
In either case, its a Controller that is interfaced with to kick off some functionality. There is a many-to-one relationship between the Controller and the View. Note the one way arrow from Controller to View. The Controller does pass back the Model, so there is knowledge between the View and the expected Model being passed into it, but not the Controller serving it up.
The input begins with the View, not the Presenter. There is a one-to-one mapping between the View and the associated Presenter. The View holds a reference to the Presenter. The Presenter is also reacting to events being triggered from the View, so its aware of the View its associated with. The Presenter updates the View based on the requested actions it performs on the Model, but the View is not Model aware. For more Reference. There are many answers to the question, but I felt there is a need for some really simple answer clearly comparing the two.
Presenter Controller : Hey View , is there any search term on that page? Presenter Controller : Hey Model , Do you have any match for this search term? Model : There is some result available, Controller. I have created a field variable in my instance and filled it with the result. Presenter : Thanks for waiting View , I found a list of matching results for you and arranged them in a presentable format: ["Piano Teacher ","Piano "]. Please show it to the user in a vertical list.
Also please hide the progress bar now [ MVP ]. Controller : Thanks for waiting View , I have asked Model about your search query. It says it has found a list of matching results and stored them in a variable named "searchResultsList" inside its instance.
You can get it from there. Also please hide the progress bar now [ MVC ]. Should the production year of the movie come first or last? Should it be in a vertical or horizontal list? Even though the sample is written for android, the underlying principles can be applied to any medium. MVC is a pattern for the architecture of a software application. It separate the application logic into three separate parts, promoting modularity and ease of collaboration and reuse.
It also makes applications more flexible and welcoming to iterations. It separates an application into the following components:. To make this a little more clear, let's imagine a simple shopping list app. All we want is a list of the name, quantity and price of each item we need to buy this week.
Below we'll describe how we could implement some of this functionality using MVC. If you want to see a sample with simple implementation please check this GitHub post. A concrete workflow of querying and displaying a list of users from a database could work like this:.
View is more loosely coupled to the model. The presenter is responsible for binding the model to the view. Also worth remembering is that there are different types of MVPs as well. Fowler has broken the pattern into two - Passive View and Supervising Controller.
When using Passive View, your View typically implement a fine-grained interface with properties mapping more or less directly to the underlaying UI widget. Your Presenter class will talk to the model and "map" it to the view. This approach is called the "Passive View". The disadvantage is that you can't leverage things like databinding which is really powerful in frameworks like WPF and Silverlight. In that case your View might have a property called Customer, which then again is databound to the UI widgets.
You don't have to think about synchronizing and micro-manage the view, and the Supervising Controller can step in and help when needed, for instance with compled interaction logic. He covered all the flavors of MVP and showed C code to implement them. In some cases the model can also be used to turn a data source into a higher level abstraction as well. A good example of this is the MVC Storefront project. The distinction made is that in an MVC application traditionally has the view and the controller interact with the model, but not with each other.
Having said that, ASP. To perhaps get an idea of the ASP. Both are patterns trying to separate presentation and business logic, decoupling business logic from UI aspects. That means that in MVP standard web form page life cycle is just enhanced by extracting the business logic from code behind. In other words, page is the one servicing http request. MVC on other hand changes completely the game because the request gets intercepted by controller class before page is loaded, the business logic is executed there and then at the end result of controller processing the data just dumped to the page "view" In that sense, MVC looks at least to me a lot to Supervising Controller flavor of MVP enhanced with routing engine.
If one would consider himself good in web forms, I would suggest MVP. If one would feel not so comfortable in things such as page life cycle etc MVC could be a way to go here. I would say that MVP in this scenario is a quick win. In MVP you can have a single view working with multiple types of presenters and a single presenter working with different multiple views. So, if for example, the model is a car, then the presenter is some sort of a car presenter, exposes the car properties year, maker, seats, etc.
The view knows that the text field called 'car maker' needs to display the presenter Maker property. You can then bind to the view many different types of presenter, all must have Maker property - it can be of a plane, train or what ever , the view doesn't care.
The view draws data from the presenter - no matter which - as long as it implements an agreed interface. MVC is great, but the problem is that usually its controller per view. Controller A knows how to set fields of View A.
At this level of granularity, MVP makes little sense. When one on the contrary go to larger scales, proper interface becomes more important, the same with unambiguous assignment of responsibilities, and here comes MVP.
On the other hand, this scale rule of a thumb, may weight very little when the platform characteristics favours some kind of relations between the components, like with the web, where it seems to be easier to implement MVC, more than MVP. The article also matches what Uncle Bob Martin said in his one of his talks: that MVC was originally designed for the small UI components, not for the architecture of the system.
In brief, it is. The simplest answer is how the view interacts with the model. In MVP the view is updated by the presenter, which acts as as intermediary between the view and the model. The presenter takes the input from the view, which retrieves the data from the model and then performs any business logic required and then updates the view.
In MVC the model updates the view directly rather than going back through the controller. IMO, MVP is an improved version of MVC where you basically separate the concern of what you're gonna show the data from how you're gonna show the view.
The presenter includes kinda the business logic of your UI, implicitly imposes what data should be presented and gives you a list of dumb view models.
And when the time comes to show the data, you simply plug your view probably includes the same id's into your adapter and set the relevant view fields using those view models with a minimum amount of code being introduced just using setters.
In MVC, we talk through interfaces boundaries to glue different layers. A controller is a plug-in to our architecture but it has no such a restriction to impose what to show. An action is performed on the Controller , which will execute an action on the Model. This example is simplified in order easily understand the concepts of this architecture. Several types of views as well as their presentation are proposed: - table with addition, modification, deletion and print , - form, - search with filter.
This example has been simplified to better explain the concepts of this architecture. Minimum version required. This page is also available for…. Close this window. Annotate the page. How to browse local help? All you have to do is configure your product as follows: Go to "Home.. The VIEW knows the presenter. The VIEW has a specific event to perform the necessary updates "Request for refreshing the display" event.
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