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.
When designing an Android app, the question often pops up :
Is it better to design a given UI component as a view or as a fragment ?
Which criteria can be used to choose the 2 ?
In which situation, in which case do you prefer one to the other ?
Note 1:
I know the format of this question may not been suitable for this stack site but I think the question is relevant for the community.
Note 2:
With this question, I am not really looking for a definitive answer (though I could be wrong), but I am looking for a collective reflection, experience sharing on that matter.
To answer you and get out of some of the nitpicking in comments:
*Views are onscreen elements. Think of them as windows. In a MVC pattern, they're the V.
*Fragments are controllers in a MVC pattern. They typically own a bunch of views, and are used to define how the user interacts with those views in the program.
*Activities are controllers in a MVC pattern. They can contain any number (including 0) of views or fragments. Fragments are used to break up an activity into separate pieces if there's a big enough subset of easily separated functionality.
I come from C Background and have knowledge on C++(at least I know virtual functions, INheritance, Code -reuse and some OOPS concept), But still I am having hard time understanding the Design Patterns in C++/Java.I guess Binders Design Patterns are based on C++ Design pattern(correct me).
DO i have to understand UML as well to understand them.
Plz explain or direct a link with test source code on the above.
PS: I am trying to understand this blog by Tetsuyuki Kobayashi and i am in no way related to him.
I wouldnt say that C++ Binders are a design pattern. I put a link here explaining them.
I would also say that Design patterns arent really language specific, they can basically be implemented in any (most) programming languages. Languages that support OOP typically make implementing design patterns easier, but that could be argued.
The Gang of Four design patterns book uses UML to explain design patterns, but I wouldnt say you would have to be a UML expert to understand design patterns. If UML is bothering you, try the Head First Design Patterns book, its much easier to understand.
We have a class home work for design pattern class. In that we have to explain anyone design pattern used in any api/framework. I was thinking if I could do the same using Android apis. I know that android uses some command, observer, template method patterns and many more but it would be great if someone could point me to the starting reference document or so.
Thank you so much in advance.
Frameworks almost by definition tend to implement high-level patterns such as MVC or ORM patterns. These are not covered in the GOF text, although you will find them in other pattern books such as Martin Fowler's Patterns of Enterprise Application Architecture. Some GOF patterns are implemented at the framework or even language-level (like C# events/delegates as an example of the Observer pattern), but mostly GOF patterns are left to the individual developer to implement as needed, as the details tend to be application or domain-specific.
Android is the same way. It has a specific flavor of Model-View-Controller built in, but not too many GOF-specific patterns. You might consider the Activity lifecycle callbacks (onStart, onResume, etc.) as a kind of Observer pattern, although with only one dedicated subscriber.
Another example might be AsyncTask, which could be considered a species of the Command Pattern. I'll leave it to you to make the connection. It is homework after all.
This link show How extensive is the use of design patterns in Java core. I will expect the android to use them extensively as well.
Examples of GoF Design Patterns in Java's core libraries
And see how Adapter pattern Specifically is being used in the Android frame (second example is from Android's source code)
http://javatechig.com/design-patterns/adapter-design-pattern-in-java
http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/5.1.1_r1/android/widget/Adapter.java?av=f
Design Patterns are just conventions which made to simplify coding. And make it more clear so you should make sure that is what they do and not obscurify your code structure.
Closed. This question needs to be more focused. It is not currently accepting answers.
Want to improve this question? Update the question so it focuses on one problem only by editing this post.
Closed 4 years ago.
Improve this 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.
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.
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 "trick" 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 "buzz-words" 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.
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 & 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
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
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)
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 Façade Design Pattern
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);
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.
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.
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
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.
Binder uses "Observer Pattern" for Death Recipient notifications.