Which Architecture patterns are used on Android

Question

I m doing a small research of mobile platforms and I would like to know which design patterns are used in Android   e g  in iOS Model-view-controller is very widely used together with delegation and other patterns    What patterns and where in particular does Android use   EDIT  I m not asking for design patterns used deep in kernel  dalvik and so on  but about patterns which an application developer will meet while developing an application

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Binder uses  Observer Pattern  for Death Recipient notifications

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Update November 2018 After working and blogging about MVC and MVP in Android for several years  see the body of the answer below   I decided to capture my knowledge and understanding in a more comprehensive and easily digestible form  So  I released a full blown video course about Android applications architecture  So  if you re interested in mastering the most advanced architectural patterns in Android development  check out this comprehensive course here  This answer was updated in order to remain relevant as of November 2016  It looks like you are seeking for architectural patterns rather than design patterns  Design patterns aim at describing a general  quot trick quot  that programmer might implement for handling a particular set of recurring software tasks  For example  In OOP  when there is a need for an object to notify a set of other objects about some events  the observer design pattern can be employed  Since Android applications  and most of AOSP  are written in Java  which is object-oriented  I think you ll have a hard time looking for a single OOP design pattern which is NOT used on Android  Architectural patterns  on the other hand  do not address particular software tasks - they aim to provide templates for software organization based on the use cases of the software component in question  It sounds a bit complicated  but I hope an example will clarify  If some application will be used to fetch data from a remote server and present it to the user in a structured manner  then MVC might be a good candidate for consideration  Note that I said nothing about software tasks and program flow of the application - I just described it from user s point of view  and a candidate for an architectural pattern emerged  Since you mentioned MVC in your question  I d guess that architectural patterns is what you re looking for    Historically  there were no official guidelines by Google about applications  architectures  which  among other reasons  led to a total mess in the source code of Android apps  In fact  even today most applications that I see still do not follow OOP best practices and do not show a clear logical organization of code  But today the situation is different - Google recently released the Data Binding library  which is fully integrated with Android Studio  and  even  rolled out a set of architecture blueprints for Android applications  Two years ago it was very hard to find information about MVC or MVP on Android  Today  MVC  MVP and MVVM has become  quot buzz-words quot  in the Android community  and we are surrounded by countless experts which constantly try to convince us that MVx is better than MVy  In my opinion  discussing whether MVx is better than MVy is totally pointless because the terms themselves are very ambiguous - just look at the answers to this question  and you ll realize that different people can associate these abbreviations with completely different constructs  Due to the fact that a search for a best architectural pattern for Android has officially been started  I think we are about to see several more ideas come to light  At this point  it is really impossible to predict which pattern  or patterns  will become industry standards in the future - we will need to wait and see  I guess it is matter of a year or two   However  there is one prediction I can make with a high degree of confidence  Usage of the Data Binding library will not become an industry standard  I m confident to say that because the Data Binding library  in its current implementation  provides short-term productivity gains and some kind of architectural guideline  but it will make the code non-maintainable in the long run  Once long-term effects of this library will surface - it will be abandoned   Now  although we do have some sort of official guidelines and tools today  I  personally  don t think that these guidelines and tools are the best options available  and they are definitely not the only ones   In my applications I use my own implementation of an MVC architecture  It is simple  clean  readable and testable  and does not require any additional libraries  This MVC is not just cosmetically different from others - it is based on a theory that Activities in Android are not UI Elements  which has tremendous implications on code organization  So  if you re looking for a good architectural pattern for Android applications that follows SOLID principles  you can find a description of one in my post about MVC and MVP architectural patterns in Android

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When i reach this post it really help me to understand patterns with example so i have make below table to clearly see the Design patterns  amp  their example in Android Framework  I hope you will find it helpful    Some useful links for reference    Common Design Patterns for Android with Kotlin Introduction to Android Design Patterns Design Patterns

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In Android the  work queue processor  pattern is commonly used to offload tasks from an application s main thread    Example  The design of the IntentService class   The  IntentService  receives the Intents  launch a worker thread  and stops the service as appropriate All requests are handled on a single worker thread

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There are various patterns used in Android framework like    Broadcast receiver uses Observer pattern Remoter service invocation uses Proxy pattern View and view group uses Composite pattern Media framework uses Facade pattern

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All these patterns  MVC  MVVM  MVP  and Presentation Model  can be applied to Android apps  but without a third-party framework  it is not easy to get well-organized structure and clean code   MVVM is originated from PresentationModel  When we apply MVC  MVVM  and 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 an 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 the 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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Here is a great article on Common Design Patterns for Android    Creational patterns    Builder  e g  AlertDialog Builder  Dependency Injection  e g  Dagger 2  Singleton   Structural patterns    Adapter  e g  RecyclerView Adapter  Facade  e g  Retrofit    Behavioral patterns    Command  e g  EventBus  Observer  e g  RxAndroid  Model View Controller Model View ViewModel  similar to the MVC pattern above

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I tried using both the model   view   controller  MVC  and model   view   presenter architectural patterns for doing android development  My findings are model   view   controller works fine  but there are a couple of  issues   It all comes down to how you perceive the Android Activity class  Is it a controller  or is it a view   The actual Activity class doesn t extend Android s View class  but it does  however  handle displaying a window to the user and also handle the events of that window  onCreate  onPause  etc     This means  that when you are using an MVC pattern  your controller will actually be a pseudo view   controller  Since it is handling displaying a window to the user  with the additional view components you have added to it with setContentView  and also handling events for at least the various activity life cycle events   In MVC  the controller is supposed to be the main entry point  Which is a bit debatable if this is the case when applying it to Android development  since the activity is the natural entry point of most applications   Because of this  I personally find that the model   view   presenter pattern is a perfect fit for Android development  Since the view s role in this pattern is    Serving as a entry point Rendering components Routing user events to the presenter   This allows you to implement your model like so   View - this contains your UI components  and handles events for them   Presenter - this will handle communication between your model and your view  look at it as a gateway to your model  Meaning  if you have a complex domain model representing  God knows what  and your view only needs a very small subset of this model  the presenters job is to query the model and then update the view  For example  if you have a model containing a paragraph of text  a headline and a word-count  But in a given view  you only need to display the headline in the view  Then the presenter will read the data needed from the model  and update the view accordingly   Model - this should basically be your full domain model  Hopefully it will help making your domain model more  tight  as well  since you won t need special methods to deal with cases as mentioned above   By decoupling the model from the view all together  through use of the presenter   it also becomes much more intuitive to test your model  You can have unit tests for your domain model  and unit tests for your presenters   Try it out  I personally find it a great fit for Android development

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I would like to add a design pattern that has been applied in Android Framework  This is Half Sync Half Async pattern used in the Asynctask implementation  See my discussion at   https   docs google com document d 1 zihWXAwgTAdJc013-bOLUHPMrjeUBZnDuPkzMxEEj0 edit usp sharing

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The Following Android Classes uses Design Patterns  1  View Holder uses Singleton Design Pattern   2  Intent uses Factory Design Pattern   3  Adapter uses Adapter Design Pattern   4  Broadcast Receiver uses Observer Design Pattern   5  View uses Composite Design Pattern   6  Media FrameWork uses Fa  ade Design Pattern

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In the Notifications case  the NotificationCompat Builder uses Builder Pattern  like   mBuilder   new NotificationCompat Builder this                       setSmallIcon R drawable ic stat notification                       setContentTitle getString R string notification                        setContentText getString R string ping                        setDefaults Notification DEFAULT ALL

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Android also uses the ViewHolder design pattern   It s used to improve performance of a ListView while scrolling it   The ViewHolder design pattern enables you to access each list item view without the need for the look up  saving valuable processor cycles  Specifically  it avoids frequent calls of findViewById   during ListView scrolling  and that will make it smooth

[android] Which Architecture patterns are used on Android?

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