How to implement MVP Passive View in an android application?

How to implement MVP Passive View in an android application? - android

I recently started building an android application and I would like to use an design pattern right from the scratch. I was told that MVP (Model-View-Presenter) is a good pattern for android applications.
I was wondering if it's possible to implement the "Passive View" variant of the MVP pattern? If I could, I would show any code.. but right now I have no idea how a passive view should look like in an android application. Also.. which role would play the MainActivity in a passive view scenario?
I would appreciate any explanations, tutorials or examples on how to implement a passive view.

MVP pattern in Android suggests that your View classes (Fragments, Activities) don't contain any presentation or business logic, but all logic is delegated to a Presenter class. The Presenter in turn calls usually void methods provided by the View when the View is initialised, an event occurs, or the View is destroyed.
So imagine a View and a Presenter implementing the following interfaces:
public interface Contract {
interface View {
void initView();
void setTextColor();
}
interface Presenter {
void init();
void onButtonClicked();
}
}
In our simplistic example the View would initialise the Presenter (dependency injection is out of scope of this post) and then call Presenter's initView method. The Presenter would be responsible for all initialisation logic like fetching data from network / storage and, if need be, update the View. When in turn the user clicks a button the View would delegate action to the Presenter by calling Presenter's onButtonClicked() method. The Presenter can do some processing and depending on the outcome maybe call View's setTextColor() method.
The most important reason for using MVP is to be able to test your logic with Junit and a mocking framework like Mockito. Your Presenter should be written in pure Java or Kotlin without any dependencies on the Android framework library. Then you can just test your Presenter by using the JVM and not having to hook up a device. This is all part of uncle Bob's clean architecture guidelines.
The two best resources for MVP are the Antonio Leiva's blog post and Google's architecture samples in github

I have a feeling that there is a fatal misunderstanding of presenters here. Even though MVP is the common standard, most people think of Presenters as Controllers or even worse a mix of Controllers, Repositories, Gateways.
A Presenter should do one thing: to present. That should be it's sole purpose. Many people unknowingly implement a MVC Architecture, calling it MVP, with limiting the data flow as following: View <-> Controller / Presenter <-> Model.. Now there is nothing wrong about this pattern, as it separates the layers of your system, if done correctly. You should be able to swap your Domain and Data layers (Android Devs usually call the layers the Presenter and Model layer) to another system and the code should still work without any dependency issues. To achieve this you have to avoid any dependency that would cause a binding to a so called detail (UI, Database, Frameworks, Hardware, Browsers, OS). Now speaking of layers, we’d usually have this data-flow hierarchy: UI -> Domain -> Data where within Android Applications we would put all our UI Code into the UI component. Now there are 2 options to position the presenter: You could abstract the View by introducing an interface for the presenters specific view. Avoid any android / hardware specific dependencies (like Contexts) within the presenter. If you achieve this, then you could say, your Presenter belongs to your Domain layer. If your Presenter knows any Android detail (or even worse a database), then you’re automatically putting it into the View layer (or even breaking your architecture, if you try to access the database from it).
Now let’s assume you abstracted your View and have your Presenter being a Domain object. Your Presenter does not care about the actual implementation of its representing View anymore, it has its abstraction and it knows where to pass the value to. Whether it’s a mobile, web or embedded App doesn’t matter anymore.
Now how does the Presenter receive data from the Data-layer and fill the UI with data? We do the same technique that we did with the View: abstractions.
We’d create an interface / abstract class of a Repository, Gateway, DataService or however you would like to call the interface of your data/model layer. You’d have POJO, your data access logic, caching, etc. Note that until now, we’re working with POJOs! We have no dependencies to any platform-binding detail (as described above). But since we need to do some caching now, we’d have to use the SQLite Manager from Android (or Room). How to do this? abstractions. Abstract any detail that causes your code to be bound to any platform.
Below you can see a picture of Uncle Bob’s proposed design of a solid software architecture. The inner layers should not have any knowledge of the outer layers.
This picture reflects the development technique I just described here, which is the same technique described in Uncle Bob’s book. We’re avoiding any dependencies to details by using their abstractions. The real implementations (Activities, Fragments, SQLiteDatabase) are being „wired“ to the inner layers from outside through dependency injection.
This technique is also called dependency inversion.
I’d recommend you to read the book „Clean Architecture“ by Robert C. Martin to develop a deeper understanding to it.

Working with MVP is not that hard
First, in the package Model, you will store all sort of POJO classes that have setters, getters and all the data structure of your app
Then comes the presenter, where you bind this objects and do some logic on it.
After you do all the logic into the presenter, it passes all that information to the View, so after that your MainActivity (the view in this case) will have just a few lines of code and your code will look really organized.
As for passive view, it means that you have the View with the less code possible to run tests in the future and have a mantenible code.
you can use MVC, MVP, MVVM, but if you want to start I would suggest you starting with MVP
Take a look at this image of MVP
You can also check THIS tutorial about MVP

Related

Injecting LiveData instances using Hilt - OK or bad?

Question
Cutting right to the chase: In Android development, is it good or bad practice to inject (ActivityScoped) LiveData instances into ViewModels using Hilt in order to observe the live data from multiple fragments?
Are there any major downsides to this approach, and is there a better way of achieving the same behavior? We could consider moving a portion or all of the code from the fragment view models to the activity view model, as the dependencies would suggest this is a better approach to begin with, but this would end up making the activity view model quite big.
Background
And some background, in case this helps to answer the question:
I have been working on an Android application in which we are using Hilt for dependency injection, Android's MVVM architecture components, and our interpretation of clean architecture which is more or less based on this article: https://www.raywenderlich.com/3595916-clean-architecture-tutorial-for-android-getting-started
Our app contains two activities and a couple of fragments, and each have been assigned their own view model. Recently as the application has grown, the code base has become a bit messy, partly due to many fragments (and their view models) depending on the same live data. The repositories and data sources injected into the view models are generally singleton, and so data sharing is not an issue.
However, what has happened is that we keep references to all view models in one activity, and many fragments are observing LiveData from each others' view models in order to update their views. This feels like a sub-optimal approach, and we are moving into refactoring season quite soon which will give us the opportunity to fix this.

Clean architecture Controller have access to the ViewModel

I have the following question, according to this image
The Controller shouldn't have access to the Presenter nor the ViewModel, however, how can I update a view with a click, i.e The user clicks a button that increases a counter in the ViewModel (since this is the class the holds the view's state) and then updates the view accordingly.
However, if the Controller has access to the Presenter, I could bypass the UseCase and call directly the Presenter, and then this class updates the ViewModel accordingly.
I've read many articles and ways to do this and mix the Controller with the Presenter seems to me that I would be breaking the Single Responsibility since the Controller would be in charge not also from creating the InputData but to add logic and call the Presenter.
How can this be done using the architecture from the picture_

The moment when you should deviate from a particular principle/architecture, is when it becomes a greater inconvenience to follow it than to not follow it. This is because project requirements shape the architecture whether we are talking about software or actual buildings. It is okay to try and make on architecture work for every situation at first, but this is mostly so you can learn when it does not suit a given situation.
Unfortunately, I do not have the full context of where that image came from, but judging by your mention of the SRP, it looks like it is either Uncle Bob's work or something closely inspired. I think you may have made the same mistake that I, and a few thousand other developers made about the SRP. To quote Clean Architecture (the book, by Uncle Bob):
Of all of the SOLID principles, the Single Responsibility Principle
(SRP) might be the least well understood. That's likely because it has
a particularly inappropriate name. It is too easy for programmers to
hear the name and then assume it means that a module should do just
one thing.
For context, the word module does not mean Gradle Module, Uncle Bob goes on to define the word as meaning a source file (in OO we can think of a class like Controller). I will leave you to research what Uncle Bob really meant with the SRP as I simply do not use the term anymore nor like to explain it. None of that is meant as disrespect to Uncle Bob; I am very fond of his work.
Returning to the question, it is hard for me to answer without knowing more context about the Controller (does it simply handle clicks and forward them to the appropriate Interactor?). I am assuming this is an Android app, in which case I would simply combine the Controller and Presenter into a single class. This is in my opinion neither a violation of Uncle Bob's SRP (which is about separating things that change for different reasons), nor would it result in a class which has low-cohesion (which concerns what a module/class/function/source does). I realize this is partly subjective, but handling UI interactions and preparing returned back end data for a ViewModel both fit under the role of Presentation Logic of a particular GUI feature in my opinion.
Failing that, ignore what I said and what the diagram is telling you and just look at the code. Does it really solve more problems to keep them separate than apart? Act accordingly.
I don't see any sensible way to follow this diagram exactly, given the requirements you have mentioned, but here is what I would do if I really had to keep the Controller and Presenter separate:
Employ the Observer (Publisher-Subscriber) Pattern between the Controller and Presenter (or maybe the Presenter and Interactor... not what I would do but this diagram does not reflect how I typically use Interactors either). You get to keep everything loosely coupled and avoid a concrete reference (i.e. drawing an arrow) between them.
You could have a Usecase which has the sole purpose of handling a mouse click and calling back to the Presenter that it occurred. I am going to be honest, this seems like a ridiculous solution. What is the point of having an Interactor that encapsulates the business logic of incrementing a counter in the UI? Unless you saved that counter every time, it does not even seem appropriate for the term business logic to begin with.
Hopefully that helps; just trying to share my past experience in case it will help.

The ViewModel's purpose is to hold data in a form convenient to UI.
If number of clicks is what UI needs - so it be, but if I understand correctly, what you want is to make this data stateful, meaning for example to save it to DB and fetch each time you need to increase it.
From this perspective, you should define an interface for your DB (a repository) plus of course an appropriate implementation (may it be a heavy DB or just a text file).
Finally, your presenter should only project the up-to-date value (mediated by the Output Data) into the ViewModel.

going with the uncle bob definition.
the click event should be part of the Controller.
the view should not update the ViewModel, it can only read it once it's updated by the presenter.
all the events should go to the controller, then the controller should access the use-case by passing the presenter object to the use-case, and the use-case should invoke the presenter, which updated the ViewModel.
the view has the access to both the Controller and the presenter.
or the controller can have the presenter object which will be passed to the use case

MVC vs MVP vs MVVM use cases

I am and android developer and I have worked on all of these three architecture patterns in my applications. Also I have gone through several post's on stackoverflow about the difference of each. My understanding might not be 100% correct but this is what I know so far in brief.
MVC - User input is received by controller. Controller updates the model then tells the view to update itself.
MVP - View gets the user input and notify the Presenter. Presenter gets the data from Model and then sends it to View. Presenter and View have one-to-one relation.
MVVM - User input is received by View. ViewModel generates the data from Model and puts out a stream of data any View subscribed to it can consume that data. View and ViewModel have one-to-many relation.
The problem is that many times in interviews I have been asked the question to tell which pattern to use when. What I think the interviewer wants to know is the type of application (like banking, e-commerce, etc) and their appropriate architecture pattern. Or at least some concrete explanation as to why I would like to use MCV in one application and MVP in another and so for MVVM.
I did my research well but could not found any proper answer on the internet that talks about the use case of each pattern. Thus, request to please tell me use case for each.

From my knowledge:
MVC: Model View Controller is the traditional old way of Android development. This was used when Android development just started and was avidly used for few years. In this time, the only well known pattern was MVC.
So, mostly all old applications started as MVC but as the code base increases, the controller(Activities/Fragments) become bulky with lot of business logic and network requests and async tasks living in them. So, such applications become difficult to maintain overtime and are very harder to test due to the high dependency between the three.
So, if your application is very small and you want to follow no new architecture patterns or have 0 understanding of those use MVC but I highly recommend not to follow MVC in this time.
MVP -> As MVC applications become difficult to maintain and test, applications transitioned towards MVP.
Model View Presenter tried to resolve the problems of MVC and moved presentation and business logic to presenters. The presenter here just performs the Interface actions and has no knowledge of the Views it is trying to update. So, as presenters are not similar to controllers we can easily test presenters and models. So, we achieve testing and maintenance benefits but it also creates a problem that now presenters are the smart one. They start becoming bulky eventually. Creating a similar problem.
Also in android, apps need to maintain app state. MVC and MVP don't come out of the box to have state saving capabilities, you need to write additional code for state maintenance.
MVVM on the other hand is most popular. Model view viewModel is the new android architecture.
You can go in detail and learn this:
https://developer.android.com/jetpack/docs/guide
Network connections live in repository. So, code is much cleaner in your fragments or activities. All three components are easily tested and maintainable.
One of the biggest advantages is you have performance benefits as it does the state saving mechanism out of the box as ViewModel follows the singleton pattern and you can achieve that by using ViewProviders and creating instance through it.
When you say what application should use what. If an application size is huge and complex would highly suggest MVVM and you can also look into other popular architecture components like MVI and clean architecture(Use case based) as well. In my opinion, an application product type doesn't change architecture requirements. It's the complexity and size that determines it. Your security requirements change based on the product.

Can I Use 3-tiers architecture and "MVC" together in Android?

It's my first real android application and i want to begin it using good design patterns because it will be a little big ,so i can manage my code easily .
Can I User 3-tiers architecture and "MVC" together in Android ?
I used it in ".net" and it was so good choice but i don't know if i can use it in android or not.
I checked this question but i still confused , i can't realize the difference between MVC and MVP , and i don't find any comment according to use n-tier with MVC or MVP to gether

There are many guides out there where people show usable architectures or worship one architecture as THE STANDARD, writing whole Books about old Methods applied to modern problems. In difference to these, this is only a rough answer:
Android encourages you to use MVC or some MVC Variant (MVP/MVVM/...) for the Activities/Fragments.
You can apply the 3-Tier Architecture on the whole App.
Presentation Layer
The MVC or variant is applied to the Presentation Layer. Your Presenter/Controller handles your view, inflation and modification, ui control bindings like onclick events, maybe some effects that are bound to this view alone and so on.
Business Layer
Here is your business logic. Your workflows, processes, rules, ...
Data Layer
And data handling goes here.
The Others
It's a good start to keep things in these 3 Layers, for both maintainability and testing. This is the basic outline of my apps, both on Android or iOS but I'm not always pressing everything into these 3 Layers. For example Components for scanning Bluetooth devices, doing downloads in the Background (or other Background services and Tasks) or adding a Camera Preview with full set of controls. I keep those separate for reuse without the troubles of writing and importing a library.

To generally answer the question, yes.
By definition of MVC (or MVP), there are three tiers (not linear, though, but in a triangle).
Presentation (View)
Logic layer (Controller / Presenter)
Data layer (Model)
There is nothing stopping a true n-tier architecture in Android. For example, you could use XML SharedPreferences flat files or SQLite as persistence data layers, then the SqliteOpenHelper class as the next tier to read&write data, which in turn would be passed to an Adapter and displayed in some ListView.
Moving off the local filesystem, you use network requests to communicate with some remote API layer which communicates with its data storage layer.

You can think that the Model and the View in MVC correspond to the Intermediate (business logic) and Presentation in 3-tier (3-layer if you prefer), respectively.
Assuming that your Model in the MVC include a data layer, then Model would correspond to both the Intermediate and Data access layer. I will call this Model1.
If you introduce the controller between this Model1 (Intermediate and Data access layer) and the View (Presentation) then you would have an MVC/3-tier architecture.
But if you prohibit the View to update the Model1, then you would have a 3-tier/MVC architecture, that is, an architecture where the view cannot update the model directly, as happens in 3-tier, and for this reason I put the name of 3-tier in front.

Android MVC Model [duplicate]

Is it possible to implement the model–view–controller pattern in Java for Android?
Or is it already implemented through Activities? Or is there a better way to implement the MVC pattern for Android?

In Android you don't have MVC, but you have the following:
You define your user interface in various XML files by resolution, hardware, etc.
You define your resources in various XML files by locale, etc.
You extend clases like ListActivity, TabActivity and make use of the XML file by inflaters.
You can create as many classes as you wish for your business logic.
A lot of Utils have been already written for you - DatabaseUtils, Html.

There is no universally unique MVC pattern. MVC is a concept rather than a solid programming framework. You can implement your own MVC on any platform. As long as you stick to the following basic idea, you are implementing MVC:
Model: What to render
View: How to render
Controller: Events, user input
Also think about it this way: When you program your model, the model should not need to worry about the rendering (or platform specific code). The model would say to the view, I don't care if your rendering is Android or iOS or Windows Phone, this is what I need you to render.
The view would only handle the platform-specific rendering code.
This is particularly useful when you use Mono to share the model in order to develop cross-platform applications.

The actions, views and activities on Android are the baked-in way of working with the Android UI and are an implementation of the model–view–viewmodel (MVVM) pattern, which is structurally similar (in the same family as) model–view–controller.
To the best of my knowledge, there is no way to break out of this model. It can probably be done, but you would likely lose all the benefit that the existing model has and have to rewrite your own UI layer to make it work.

After some searching, the most reasonable answer is the following:
MVC is already implemented in Android as:
View = layout, resources and built-in classes like Button derived from android.view.View.
Controller = Activity
Model = the classes that implement the application logic
(This by the way implies no application domain logic in the activity.)
The most reasonable thing for a small developer is to follow this pattern and not to try to do what Google decided not to do.
PS Note that Activity is sometimes restarted, so it's no place for model data (the easiest way to cause a restart is to omit android:configChanges="keyboardHidden|orientation" from the XML and turn your device).
EDIT
We may be talking about MVC, but it will be so to say FMVC, Framework--Model--View--Controller. The Framework (the Android OS) imposes its idea of component life cycle and related events, and in practice the Controller (Activity/Service/BroadcastReceiver) is first of all responsible for coping with these Framework-imposed events (such as onCreate()). Should user input be processed separately? Even if it should, you cannot separate it, user input events also come from Android.
Anyway, the less code that is not Android-specific you put into your Activity/Service/BroadcastReceiver, the better.

There is no single MVC pattern you could obey to. MVC just states more or less that you should not mingle data and view, so that e.g. views are responsible for holding data or classes which are processing data are directly affecting the view.
But nevertheless, the way Android deals with classes and resources, you're sometimes even forced to follow the MVC pattern. More complicated in my opinion are the activities which are responsible sometimes for the view, but nevertheless act as an controller in the same time.
If you define your views and layouts in the XML files, load your resources from the res folder, and if you avoid more or less to mingle these things in your code, then you're anyway following an MVC pattern.

You can implement MVC in Android, but it is not "natively supported" and takes some effort.
That said, I personally tend towards MVP as a much cleaner architectural pattern for Android development. And by saying MVP I mean this:
I have also posted a more detailed answer here.
After playing with the various approaches to MVC/MVP implementation in Android, I came up with a reasonable architectural pattern, which I described in a this post: MVP and MVC Architectural Patterns in Android.

The best resource I found to implement MVC on Android is this post:
I followed the same design for one of my projects, and it worked great. I am a beginner on Android, so I can't say that this is the best solution.
I made one modification: I instantiated the model and the controller for each activity in the application class so that these are not recreated when the landscape-portrait mode changes.

I agree with JDPeckham, and I believe that XML alone is not sufficient to implement the UI part of an application.
However, if you consider the Activity as part of the view then implementing MVC is quite straightforward. You can override Application (as returned by getApplication() in Activity) and it's here that you can create a controller that survives for the lifetime of your application.
(Alternatively you can use the singleton pattern as suggested by the Application documentation)

MVC- Architecture on Android
Its Better to Follow Any MVP instead MVC in android. But still according to the answer to the question this can be solution
Description and Guidelines
Controller -
Activity can play the role.
Use an application class to write the
global methods and define, and avoid
static variables in the controller label
Model -
Entity like - user, Product, and Customer class.
View -
XML layout files.
ViewModel -
Class with like CartItem and owner
models with multiple class properties
Service -
DataService- All the tables which have logic
to get the data to bind the models - UserTable,
CustomerTable
NetworkService - Service logic binds the
logic with network call - Login Service
Helpers -
StringHelper, ValidationHelper static
methods for helping format and validation code.
SharedView - fragmets or shared views from the code
can be separated here
AppConstant -
Use the Values folder XML files
for constant app level
NOTE 1:
Now here is the piece of magic you can do. Once you have classified the piece of code, write a base interface class like, IEntity and IService. Declare common methods. Now create the abstract class BaseService and declare your own set of methods and have separation of code.
NOTE 2: If your activity is presenting multiple models then rather than writing the code/logic in activity, it is better to divide the views in fragments. Then it's better. So in the future if any more model is needed to show up in the view, add one more fragment.
NOTE 3: Separation of code is very important. Every component in the architecture should be independent not having dependent logic. If by chance if you have something dependent logic, then write a mapping logic class in between. This will help you in the future.

Android UI creation using layouts, resources, activities and intents is an implementation of the MVC pattern. Please see the following link for more on this - http://www.cs.otago.ac.nz/cosc346/labs/COSC346-lab2.2up.pdf
mirror for the pdf

Android's MVC pattern is (kind-of) implemented with their Adapter classes. They replace a controller with an "adapter." The description for the adapter states:
An Adapter object acts as a bridge between an AdapterView and the
underlying data for that view.
I'm just looking into this for an Android application that reads from a database, so I don't know how well it works yet. However, it seems a little like Qt's Model-View-Delegate architecture, which they claim is a step up from a traditional MVC pattern. At least on the PC, Qt's pattern works fairly well.

Although this post seems to be old, I'd like to add the following two to inform about the recent development in this area for Android:
android-binding - Providing a framework that enabes the binding of android view widgets to data model. It helps to implement MVC or MVVM patterns in android applications.
roboguice - RoboGuice takes the guesswork out of development. Inject your View, Resource, System Service, or any other object, and let RoboGuice take care of the details.

Model View Controller (MVC)
Description:
When we have to main large projects in the software development, MVC
is generally used because it’s a universal way of organizing the
projects.
New developers can quickly adapt to the project
Helps in development of big projects and cross platform too.
The MVC pattern is essentially this:
Model: What to display. This can be the data source (Ex: Server, Raw
data in the app)
View: How it’s displayed. This can be the xml. It is thus acting as a
presentation filter. A view is attached to its model (or model part)
and gets the data necessary for the presentation.
Controller: Handling events like user input. This be the activity
Important feature of MVC: We can modify Either the Model or View or Controller still not affecting the other ones
Say we change the color in the view, size of the view or the position
of the view. By doing so it won’t affect the model or the controller
Say we change the model (instead of data fetched from the server
fetch data from assets ) still it won’t affect the view and
controller
Say we change the Controller(Logic in the activity) it won’t affect
the model and the view

It was surprising to see that none of the posts here answered the question. They are either too general, vague, incorrect or do not address the implementation in android.
In MVC, the View layer only knows how to show the user interface (UI). If any data is needed for this, it gets it from the Model layer. But the View does NOT directly ask the model to find the data, it does it through the Controller. So the Controller calls the Model to provide the required data for the View. Once the data is ready, the Controller informs the View that the data is ready to be acquired from the Model. Now the View can get the data from the Model.
This flow can be summarised as below:
It is worth noting that the View can know about the availability of the data in the Model either through Controller -- also known as Passive MVC -- or by observing the data in the Model by registering observables to it, which is Active MVC.
On the implementation part, one of the first things that comes to mind is that what android component should be used for the View? Activity or Fragment ?
The answer is that it does not matter and both can be used. The View should be able to present the user interface (UI) on the device and respond to the user's interaction with the UI. Both Activity and Fragment provide the required methods for this.
In the example app used in this article I have used Activity for the View layer, but Fragment can also be used.
The complete sample app can be found in the 'mvc' branch of my GitHub repo here.
I have also dealt with the pros and cons of MVC architecture in android through an example here.
For those interested, I have started a series of articles on android app architecture here in which I compare the different architectures, i.e. MVC, MVP, MVVM, for android app development through a complete working app.

I think the most useful simplified explanation is here:
http://www.cs.otago.ac.nz/cosc346/labs/COSC346-lab2.2up.pdf
From everything else I've seen and read here, implementing all these things makes it harder and does not fit in well with other parts of android.
Having an activity implement other listeners is already the standard Android way. The most harmless way would be to add the Java Observer like the slides describe and group the onClick and other types of actions into functions that are still in the Activity.
The Android way is that the Activity does both. Fighting it doesn't really make extending or doing future coding any easier.
I agree with the 2nd post. It's sort of already implemented, just not the way people are used to. Whether or not it's in the same file or not, there is separation already. There is no need to create extra separation to make it fit other languages and OSes.

Being tired of the MVx disaster on Android I've recently made a tiny library that provides unidirectional data flow and is similar to the concept of MVC: https://github.com/zserge/anvil
Basically, you have a component (activity, fragment, and viewgroup). Inside you define the structure and style of the view layer. Also you define how data should be bound to the views. Finally, you can bind listeners in the same place.
Then, once your data is changed - the global "render()" method will be called, and your views will be smartly updated with the most recent data.
Here's an example of the component having everything inside for code compactness (of course Model and Controller can be easily separated). Here "count" is a model, view() method is a view, and "v -> count++" is a controller which listens to the button clicks and updates the model.
public MyView extends RenderableView {
public MyView(Context c) {
super(c);
}
private int count = 0;
public void view() {
frameLayout(() -> { // Define your view hierarchy
size(FILL, WRAP);
button(() -> {
textColor(Color.RED); // Define view style
text("Clicked " + count); // Bind data
onClick(v -> count++); // Bind listeners
});
});
}
With the separated model and controller it would look like:
button(() -> {
textColor(Color.RED);
text("Clicked " + mModel.getClickCount());
onClick(mController::onButtonClicked);
});
Here on each button click the number will be increased, then "render()" will be called, and button text will be updated.
The syntax becomes more pleasant if you use Kotlin: http://zserge.com/blog/anvil-kotlin.html. Also, there is alternative syntax for Java without lambdas.
The library itself is very lightweight, has no dependencies, uses no reflection, etc.
(Disclaimer: I'm the author of this library)

According to the explanation that the Xamarin team explained (on the iOS MVC "I know it seems weird, but wait a second"):
The model (data or application logic),
The view (user interface), and
The controller (code behind).
I can say this:
The model on Android is simply the parcelable object. The view is the XML layout, and the controller is the (activity + its fragment).
*This is just my opinion, not from any resource or a book.

There is not an implemented MVC architecture, but a set of libraries / examples exists to implement an MVP (model–view–presenter) architecture.
Please, check these links:
https://github.com/sockeqwe/mosby
https://github.com/android10/Android-CleanArchitecture
https://github.com/antoniolg/androidmvp
Google added an example of an Android architecture MVP:
https://github.com/googlesamples/android-architecture

I have seen that many people are saying MVC is already implemented in Android, but it's not true. Android follows no MVC by default.
Because i don't Google will ever forcefully impose the restrictions of an MVC implementation like iPhone, but its upto the developers which patteren or technique they want in their project, In small or simple applications use of MVC is not required, but as the application grows and get complicated and require modification's of its code in later years, then there comes a need of the MVC pattern in Android.
It provides an easy way to modify code and also helps in reduction of issues.
If you would like to implement MVC on Android, then follow this below given link and enjoy the MVC implementation in your project.
http://www.therealjoshua.com/2011/11/android-architecture-part-1-intro/
But nowadays i think MVP along with Android Architectural Pattern is one of the best option developers should use for a clean and robust android applications.

When we apply MVC, MVVM, or Presentation Model to an Android app, what we really want is to have a clear structured project and more importantly easier for unit tests.
At the moment, without a third-party framework, you usually have lots of code (like addXXListener(), findViewById(), etc.), which does not add any business value.
What's more, you have to run Android unit tests instead of normal JUnit tests, which take ages to run and make unit tests somewhat impractical. For these reasons, some years ago we started an open source project, RoboBinding - A data-binding Presentation Model framework for the Android platform.
RoboBinding helps you write UI code that is easier to read, test and maintain. RoboBinding removes the need of unnecessary code like addXXListener or so, and shifts UI logic to Presentation Model, which is a POJO and can be tested via normal JUnit tests. RoboBinding itself comes with more than 300 JUnit tests to ensure its quality.

In my understanding, the way Android handles the MVC pattern is like:
You have an Activity, which serves as the controller. You have a class which responsibility is to get the data - the model, and then you have the View class which is the view.
When talking about the view most people think only for its visual part defined in the xml. Let's not forget that the View also has a program part with its constructors, methods and etc, defined in the java class.

Develop Reference

The Android operating system is a mobile operating system that was developed by Google (GOOGL?) to be primarily used for touchscreen devices, cell phones, and tablets.