MVC pattern on Android

Question

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

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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.

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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

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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

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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

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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

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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

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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

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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

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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    - gt                    Define your view hierarchy       size FILL  WRAP         button    - gt              textColor Color RED           Define view style           text  Clicked     count       Bind data           onClick v - gt  count            Bind listeners                         With the separated model and controller it would look like   button    - gt       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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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