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.
Related
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.
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.
I would like to know if someone know some Android Framework to conventional applications. For example, a framework like rails which we can see easily the MVC pattern.
See answer here for an overview of Android's limitations, which will give you an idea of why an MVC pattern on Android has not yet emerged: http://www.quora.com/Is-there-any-standard-MVC-framework-in-Android-application-development-If-not-is-it-worth-developing-one
After having posted that answer I have gone ahead and built a fully-featured app using a single-Activity architecture. It allowed us to get past all the major UX limitations that were mentioned while being able to have arbitrary complexity in controller hierarchies (parents with children with sub-children etc.). Overall it worked out great, however you WILL have to build out specialized components (ie: custom back stack mechanism) as well as to store/restore state in a way that plays nicely with Android's own Activity/Fragment lifecycle patterns. There are also certain limitations around Fragment animations which had us pull our hair out at times, which required more custom component workarounds. ie: animations that show both an outgoing and incoming Fragment on-screen at the same time aren't supported on Android, so you will have to resort to taking screenshots of views and placing them into temporary ImageViews so that you create the appearance of transitions that show two fragments at the same time. In the end it's all possible, but you will have to be ready to work around annoying Android limitations while keeping an overall MVC architecture intact.
In summary: make your top-level component an Activity which is primarily responsible for top-level navigation (tab-based, menu-based, etc., as well as back stack and state preservation). The top-level component should not govern any particular screen of your app, instead it manages controllers for every top-level screen. The controllers are all Fragments, and can contain sub-controllers which are also Fragments. All screen transitions are performed using fragment transactions as opposed to Intents/Activities. Passing around data between Fragments is another point of contention as Android generally only supports data-passing through an Activity (ie: Fragment uses its parent Activity). But in this architecture you have need to have Fragments passing data to each other (either parent/child or sibling-sibling relationships).
I don't have this wrapped up into a framework or anything, but if your dev/arch team is sufficiently proficient the architecture is definitely worthwhile shooting for. You will come out with an app that is not subject to the traditional UX limitations of Android... something that very few Android apps can say they've achieved. Also... it generally feels awesome showing you can achieve the same level of UX that iOS apps have for years. It's about time isn't it??
Don't know about the "conventional" part - Android does not play well with MVC architecture natively (mostly because Activities and Fragments take on responsibilities of both views and controllers), and I don't know if there is a standard framework for implementing MVC in Android.
I described some of my insights in more details in this answer.
That said, I created MVC (in fact MVP) template/tutorial application which demonstrates the approach I take to enforce MVP in my apps. You can use this app as tutorial, or clone/fork it and use as Android Studio template for your own apps. The source code is here: https://github.com/techyourchance/android_mvc_template
basically android has MVC pattern, but if you need more features like .net mvc you can use com.divankits.mvc module. Just see one of samples to find out how to use it.
here is more details about module:
bind properties to view(layout) objects
you are able to create field validators
convert model to json
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In the same way a web or desktop app might have three or n tiers - UI, Business, Data for example - what is the suggested structure for an Android application? How do you group classes together, what layers do you have etc?
I'm just starting Android dev (an internet-based app that must respond to incoming notifications) and have no real feel for the structure I'm aiming at. Suggestions appreciated.
IMHO, Android "wants to" follow a MVC pattern, but view & controller are generally really coupled in activities.
It makes unit test harder and it's hard to obey to the Single Responsibility Principle.
I found a really nice Android architecture presented here, there could be an idea. Everything is loosely coupled, so much easier to test and edit.
Obviously, I'm sure there are a lot of others possibilities (like the MVP pattern (Model View Presenter) - and here are answers talking about MVP in Android), but you should still take a look on it.
I've been working on Android for 9 months now from a server-side background where full unit testing and layered architectures are common and work well.
Through lots of trial and error and I would strongly suggest using the Model View Presenter pattern, not Model View Controller.
A huge issue I've found is that Activities/Fragments have a lifecycle which is outside your control and can lead to unexpected issues.
For example, our main android app wants to be used in landscape mode on tablets. We do this in OnCreateView() or OnCreate().
On a Nexus 7, the default view is portrait so what happens is that it starts the activity in portrait mode, our code then says go to landscape and android ultimately creates the activity class 3 times!
We've hooked up network requests to onCreate and they end up happening 3 times in this case.
Sure, we can add logic to look for duplicate calls but, in my opinion, it would be better, architecturally to try and divide the UI from the business logic.
My recommendation would be to use the factory pattern to create presenters from the activity but make sure the factory only ever returns the same instance. The presenter can then contain logic to do network request, look for duplicates and return cached results and general business logic.
When results from network calls return, either post to a bus such as Otto which the activity (register for the event on onResume() and deregister during onPause()) has registered to, or make sure the callback interface implemented by the activity has been updated to the last activity in the presenter.
This way, code in the presenter downwards is unit testable and not reliant on flaky UI layer testing.
The actions, views and activies in Android are the baked in way of working with the Android UI and are an implementation of a model-view-viewmodel pattern, which is structurally similar (in the same family as) model view controller.
To the best of my knoweledge, 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.
You can find MVC in the followings:
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 store data in SQLite or your custom data in /assets/ folder, read more about resources and assets
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 model, and have your own packages, that will act as a structure
A lot of Utils have been already written for you. DatabaseUtils, Html,
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 oppinion are the activites 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 this things in your code, then your anyway following a MVC pattern.
MVP is the latest architecute most people are following
Here is the small documentation As Uncle Bob's clean architecture says, “Architecture is About Intent, not Frameworks”
Watch this video it's just mindblowing good.
Here is a dedicated project for Android Architecture blueprints with well documented source codes. All of them are based on the MVP pattern with several twists. Also check the comparison of the various solutions based on lines-of-code, testability, cost of learning, their support for increasing data complexity. It depends on the particularly developed app and the context (time to market, developers, future plans, etc.) which blueprint fits best.
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I was a JaveEE developer. Recently I joined an Android development team. The structure of Android confused me. The MVC design pattern doesn't seem to suit for Android development. So what is the design pattern principle for Android development? I mean is there any hint about how to write a clean, easy reading and effective Android code.
Android's architecture annoyed me at first, but I beginning to see a method to their madness. It's poorly explained by the android documentation. My biggest gripe has always been that it's hard to have a centralized data model with objects that your Activities share just like a normal application. Android seemed to want me to be a nomad because I could only share primitives between my Activities. And dropping junk in a database is NOT a model because it contains no behavior. So as most people my business logic all ends up in my activity making it hard to share business logic in other activities.
I've come to find out I was missing some key puzzle pieces. Android is MVC. However, it's coupled to the View fairly heavily.
Activity == Controller
Model == Subclass of Application
Anything that subclasses View == View
Interestingly you can create a subclass of Application and declare this in your Manifest file, and Android will create a single instance of this object that lives the length of your application no matter what Activity is destroyed or created. That means you can build a centralized data model there that all Activities have access to.
The way I see this is something like a primitive Spring container that you can initialize objects and resolve dependencies between them. That way you can decouple the model portion of your application away from the Activity themselves. And just have the Activity make calls on the model, and hand callbacks to receive the results so it can update the UI.
The problems with Android is that it mixes controller and view pretty heavily. For example, subclasses like TabActivity, ListActivity imply a certain view being used. So swapping out a view is pretty involved. Also the Controller makes very specific assumptions about what the view is even if you use Activity. He contains direct references to UI objects like TextView, etc. And it registers for low level events like clicks, keyboard, etc.
It would be better if Activity could register for more high level events like "Login", "Update Account Balance", etc which the view would dispatch in response to a series of clicks, keyboard, touch events. That way the controller works at the level you might describe features instead of design features.
I think we'll reach this type of design eventually as we better understand come up with better tools and techniques. It seems like Android might have the extensibility to make this happen, but it's up to community to chart it.
The actions, views and activies in Android are the baked in way of working with the Android UI and are an implementation of a model-view-viewmodel pattern, which is structurally similar (in the same family as) model view controller.
To the best of my knoweledge, 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.
You can find MVC in the followings:
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 store data in SQLite or your custom data in /assets/ folder, read more about resources and assets
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 model, and have your own packages, that will act as a structure
A lot of Utils have been already written for you. DatabaseUtils, Html,
There is no single MVC Pattern you could obey to. MVC just states more or less that you shouldn't 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 activites 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 this things in your code, then you're anyway following a MVC pattern.
Android development is primarily GUI development, which like Swing/AWT in Java consists of lots of anonymous inner classes reacting to GUI events. Its one of the things that has really kept me away from doing a lot with Swing....but I have an Android phone, so I'm going to grit my teeth and just get over it, as many an Apple fanboy has said about the antenna problems. ;)
Android makes the typical decision of making the Controller and the View a single class. This encourages putting too much in the same place. An Activity corresponds to a screen, each View to a region of a screen (sometimes the whole screen), each Controller to the user gestures from that region of the screen, and Models are just Models, sometimes backed by services from Environment or some other crazy little set of utility functions. I use the Activity to coordinate one or more MVC trios. This helps deal with Android's choice to just throw everything in the same place.
I can test the vast majority of an Android app without running the simulator. Big win.
Sorry for my English.
Android has a very good modularity (Activities, Fragments, Views, Services, etc.). So there is no need in MVC.
Of course there is the separation of taking input (Activities, Fragments), logic, view (xml or java) and data (databases, files, preferences). But this is not MVC. You shouldn't try to use MVC, it will only complicate your architecture.
Rather than keeping something in global scope, Android motivates you to keep objects as deep as possible in their scopes (class members, local variables), and pass objects to/from activities, or to fragments, using Intents/Bundles. This is also because of memory limitation.
The system may destroy your activity if the foreground activity
requires more resources so the system must shut down background
processes to recover memory.
So it's not safe to store not-constant (mutable) objects as global (static) objects. Usually you use static for immutable constants.
In simple terms, you separate your application into screens (Activities). Then each screen - into fragments (Fragments). To perform a sequence of actions on the screen you can also separate them using Fragments (example).
So you have very small blocks in your application, each of which you can easily test and reuse.
My impression is that android programming model has lots of similarity with MS WPF.
XML layout definitions, code that is always bound to one of these definitions...
So, if you are asking about design patterns because you want to improve your current or in development android projects, maybe you should look at WPF practices and patterns for improved architecture, like MVVM.
Check out these links:
http://msdn.microsoft.com/en-us/magazine/dd419663.aspx
there is small project that is already trying similar thing:
http://code.google.com/p/android-binding/
cheers