Application be and you android

Modularizing Android Applications

We’ve all been there. Single module android applications — at some point in our Android development career it’s likely we’ve worked on, or are working on, a project that consists of a single module. Now, there’s nothing wrong with that at all and in a lot of cases, a single module will most likely do the job.

But in cases where our applications may grow, or we may want to take advantage of new distribution features (Instant apps, app bundles) from Google, or even just create a clear separation of concerns to make our project easier to work with— modularizing our applications can help us to achieve all of these things. And because some of these newer tools from Google are aimed at modularized applications, who knows what may become available in the future for applications that are structured this way.

Recently I’ve playing with Instant Apps as well as the new App Bundles, which means there are now more ways to modularize our projects — and knowing a little bit more about these can help us to know the right ways to configure our projects. Maybe you want to modularize your application, or maybe you want to get a clearer understanding on the differences between the different modules that we can create for our project — in this post we’re going to take a quick look at the different kinds of modules we can create and what these can do for our android applications.

Application module

We’ll start here as it’s likely a module that you’ve already encountered or used at some point during your development career. And if not, then it’s the most important place to start! This is essentially the main module of your application and will often be under the app module, using the application plugin in the modules build.gradle file to signify this:

Now if you’re building a single module application then this will be the only module-type plugin that you will be using throughout your project. In single module projects, this base module will contain all of your applications responsibilities — be in User Interface, Networking, Cache, Data operations — you name it and it will be there.

If you’re building a multi-module application, then the application module will still be the installed module, but the way this application module operates will vary depend on what it is you are building:

• If your multi-module project simply abstracts out data responsibilities of your application into data modules, then the application module will operate in the same way that you have worked with it in single-application modules but just with a clearer seperation of concerns.
• If your multi-module project is supporting dynamic feature modules then this application module will behave in pretty much the same way as the single module application . The only difference is that the module will need to define the module references for the dynamic features that are to be supporting for the application instance.
• If your multi-module project is for instant apps then this application module will simply be used to define the feature-module dependencies for the instant app. This is because when an instant app is being built, this application module does not contain any application code as its responsibility is just consume the feature modules which are declared.

Core modules

You can essentially use these modules to separate out related areas of your project so that they are decoupled from the main module of your project. There’s not really a coined term for these but lets call them core modules.

For example, let’s say you have a project that supports both Android wear and Android Phones, you might have a module for the Wear UI layer, Phone UI layer followed by a core module. This core module will contain all of the shared business logic, data operations, caching etc that is used by both of the UI modules. In this case, you are promoting code re-use as all of these aspects can be shared between the two UI modules.

Re-use isn’t the only reason as to why you might want to create this kind of module though. Separating core logic can also help to create a clear separation of concerns that makes your code easier to understand, test and maintain across your team — you may also benefit from build time improvements in some cases.

So for example, you may have a large application with a complex data layer that communicates with both a remote and cache data source. In cases like this, separating out these parts of logic into their own responsibility-specific modules allows you to achieve these things. This could result in us having a data module (to handle the fetching of data and data source), remote module (to handle remote data source communication) and cache module (to handle local data persistence) alongside a presentation module to handle the user-facing parts of our application.

There are no strict guidelines as to what should be in these core modules. My advice would be to not move stuff out into module for the sake of it, but if you feel there will be some benefit for your team (like the ones mentioned above) then moving a responsibility into a module can help you to achieve some of the benefits of modularization.

Core modules that contain android framework references will need to use the library plugin:

Whilst on the other hand, core modules that do not reference the android framework can simply be pure kotlin / java modules:

Abstraction modules

Core modules may often be used to move chunks of shared logic or independent responsibilities, but sometimes we may want to abstract some third-party responsibility out of our application. This can often be a good idea so that our application will not be tightly coupled to a specific implementation of something— in this situation we’d simply communicate via an interface between the app and abstraction module, allowing us to easily switch out the implementation for another if required. Therefore if some library becomes deprecated, a service shuts down or for whatever reason you need to change the implementation then you can do so with minimal interruptions to your code base.

In these cases, your abstraction modules will either use the android library plugin or simply be a pure kotlin / java module (depending on the library dependencies) that we previously looked at.

Feature Modules

As well as this approach to splitting out back-end related tasks into core modules, you can do the same for user facing features within your app — we call these feature modules. These feature modules are going to contain specific features of our application which can help us to again decouple different responsibilities to achieve the same benefits as we’ve previously looked at. Now, the way that these are defined will depend on the kind of multi-project application that you are building, so let’s take a look at the different scenarios:

Standard application

In a ‘standard’ application where you are not using instant apps or dynamic delivery, you may still want to split individual features out into modules to achieve some of the benefits from modularization, whilst also future-proofing yourself incase your app moves in an instant/dynamic direction along the line. In these cases you will simply package up a feature into an android library module and add it as a dependency to your application module.

In cases where you are not supporting instant apps, or not ready (or need) to support dynamic delivery yet, featuring by library modules can still help you to decouple your codebase and achieve other benefits of modularization. In these cases you can simply declare modules as library modules using the library plugin and add them as a dependency to your application module.

Instant support application

On the other hand, if your app supports Play Instant then you will need to use the feature plugin for your desired feature module:

Each feature module will need to have a reference to your base module (in this diagram, the app module) — the feature module in this case will only contain the required code for the implementation of that feature, any code that is required from the core of your app will be obtained from the base module reference.

Dynamic support application

These kind of modules can be used to decouple specific features and resources of your application into their own module, to then be used as part of the new App Bundle format which allows us to dynamically deliver individual features to users. This means we can reduce the initial install size of our applications, instead allowing users to download specific features at run-time as and when they are required.

Just like the instant app focused feature module, these dynamic-feature modules will contain pure feature implementations whilst still having a reference to the base module of the application. The only difference within this module is that the manifest file contained within it has some additional information regarding the distribution of this module.

We can define a module as a dynamic feature module by using the provided plugin below:

Note: In future app bundles will provide support for instant apps.

Instant App Module

Last but not least, if you’re currently wanting to support instant apps then your application will need to be provide an instant module.

The contents of this module will be pretty empty most of the time — this is because the responsibility of the Instant Module is to simply build the instant app when request. Therefore, its sole purpose is to consume the feature modules that have been referenced as a dependency. When defining an instant module you will need to use the instant app plugin in your modules build.gradle file:

The aim of this article was to provide a brief overview of the different modules that are available for android projects, as well as plant some seeds as to how you could approach modularization within your app. If you have any questions about modularization then please do reach out 🙂

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Android Application Class

W hile Starting App development, we tend to miss out simple basic stuffs either by ignorance or by curiosity to build million dollar app. But, Hey! Why so serious !. Building a App is bit of Art ,bit of Engineering and frequently both.

Activity Life Cycle is stages of activity in run time, knowing these would save you from headaches while you dive deeper in development.

I have written a post that will help you to understand activity lifecycle in a practical approach. Check it out

Android Activity Lifecycle

Android activity lifecycle is first thing to be known as android developer. Here I’m sharing with you some facts and…

Application class is a base class of Android app containing components like Activities and Services. Application or its sub classes are instantiated before all the activities or any other application objects have been created in Android app.

You Don’t have to import or extend application class, they are predefined. We cannot change application class but we could give additional instruction to it by extending it. Refer here for more info.

Create a java class named SubApplication and Application as Superclass

By extending Application class you could get boilerplate code like this

Check in AndroidManifest.xml and set Application name to SubApplication that you created

Lets take a situation where we should know which activity is currently running and we have to use register network receiver in all our activities. To this we used to write same code in all the activities or write a base class and extend that class instead of extending AppCompactActivity.

We have Activity Life cycle in one hand and Application class in another, what sense they make? Well actually they do? Let’s look into it.

1. In application class create static Activity variable it is accessible from whole project.

2. Register Activity Life Cycle callback in onCreate method in application class. By this step we can get currently running activity in our app from mActivity.

3.Moving on to next, Create a Broadcast Receiver and write a method to check the internet connection. you can get the code here .

4. Register your broadcast receiver in Manifest File

But for SDK Above Nougat we need to register receiver and unregister in every activity we use programmatically or We can just register and unregister Commonly in Application class.

5. Create a Object for Broadcast Receiver in application class and Register it in onResume method and Unregister in onPause method.

Bit confused! Don’t Worry, Here is the Link to the files.

Thanks for reading out the article. Let me know if I have missed out something interesting so that I can be added. Be sure to clap/recommend as much as you can and also share with your friends.

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Android Application Launch explained: from Zygote to your Activity.onCreate()

Apr 30, 2018 · 6 min read

This article explains how Android launches your application when a user clicks an app icon. The Android system does a lot of heavy lifting behind the curtains to make your launch activity visible to a user. This article covers this process in detail by highlighting the important phases and call sequences.

Android applications are unique in two ways:

1. Multiple Entry points: Android apps are composed of different components and they can invoke the components owned by other apps. These components roughly correspond to multiple entry points for any application. Hence, they differ from traditional applications which have a single entry point like main() method.
2. Own Little World: Every Android application lives in its own world, it runs in a separate process, it has its own Dalvik VM instance and is assigned a unique user ID.

When does Android process start?

An Android process is started whenever it is required.

Any time a user or some other sys t em component requests a component (could be a service, an activity or an intent receiver) that belongs to your application be executed, the Android system spins off a new process for your app if it’s not already running. Generally processes keep running until killed by the system. Application processes are created on demand and a lot of things happen before you see your application’s launch activity up and running.

Every app runs in its own process: By default, every Android app runs in its own Android process which is nothing but a Linux process which gets one execution thread to start with. For example, when you click on a hyper-link in your e-mail, a web page opens in a browser window. Your mail client and the browser are two separate apps and they run in their two separate individual processes. The click event causes Android platform to launch a new process so that it can instantiate the browser activity in the context of its own process. The same holds good for any other component in an application.

Zygote : Spawning new life, new process

Let’s step back for a moment and have a quick look on system start-up process. Like the most Linux based systems, at startup, the boot loader loads the kernel and starts the init process. The init then spawns the low level Linux processes called “daemons” e.g. android debug daemon, USB daemon etc. These daemons typically handle the low level hardware interfaces including radio interface.

Init process then starts a very interesting process called ‘ Zygote ’.

As the name implies it’s the very beginning for the rest of the Android application. This is the process which initializes a very first instance of Dalvik virtual machine. It also pre-loads all common classes used by Android application framework and various apps installed on a system. It thus prepares itself to be replicated. It stats listening on a socket interface for future requests to spawn off new virtual machines (VM)for managing new application processes. On receiving a new request, it forks itself to create a new process which gets a pre-initialized VM instance.

After zygote, init starts the runtime process.

The zygote then forks to start a well managed process called system server. System server starts all core platform services e.g activity manager service and hardware services in its own context.

At this point the full stack is ready to launch the first app process — Home app which displays the home screen also known as Launcher application.

When a user clicks an app icon in Launcher …

The click event gets translated into startActivity(intent) and it is routed to ActivityManagerService via Binder IPC. The ActvityManagerService performs multiple steps

1. The first step is to collect information about the target of the intent object. This is done by using resolveIntent() method on PackageManager object. PackageManager.MATCH_DEFAULT_ONLY and PackageManager.GET_SHARED_LIBRARY_FILES flags are used by default.
2. The target information is saved back into the intent object to avoid re-doing this step.
3. Next important step is to check if user has enough privileges to invoke the target component of the intent. This is done by calling grantUriPermissionLocked() method.
4. If user has enough permissions, ActivityManagerService checks if the target activity requires to be launched in a new task. The task creation depends on Intent flags such as FLAG_ACTIVITY_NEW_TASK and other flags such as FLAG_ACTIVITY_CLEAR_TOP.
5. Now, it’s the time to check if the ProcessRecord already exists for the process.If the ProcessRecord is null, the ActivityManager has to create a new process to instantiate the target component.

As you saw above many things happen behind the scene when a user clicks on an icon and a new application gets launched. Here is the full picture :

There are three distinct phases of process launch :

1. Process Creation
2. Binding Application
3. Launching Activity / Starting Service / Invoking intent receiver …

ActivityManagerService creates a new process by invoking startProcessLocked() method which sends arguments to Zygote process over the socket connection. Zygote forks itself and calls ZygoteInit.main() which then instantiates ActivityThread object and returns a process id of a newly created process.

Every process gets one thread by default. The main thread has a Looper instance to handle messages from a message queue and it calls Looper.loop() in its every iteration of run() method. It’s the job of a Looper to pop off the messages from message queue and invoke the corresponding methods to handle them. ActivityThread then starts the message loop by calling Looper.prepareLoop() and Looper.loop() subsequently.

The following sequence captures the call sequence in detail —

The next step is to attach this newly created process to a specific application. This is done by calling bindApplication() on the thread object. This method sends BIND_APPLICATION message to the message queue. This message is retrieved by the Handler object which then invokes handleMessage() method to trigger the message specific action — handleBindApplication(). This method invokes makeApplication() method which loads app specific classes into memory.

This call sequence is depicted in following figure.

Launching an Activity:

After the previous step, the system contains the process responsible for the application with application classes loaded in process’s private memory. The call sequence to launch an activity is common between a newly created process and an existing process.

The actual process of launching starts in realStartActivity() method which calls sheduleLaunchActivity() on the application thread object. This method sends LAUNCH_ACTIVITY message to the message queue. The message is handled by handleLaunchActivity() method as shown below.

Assuming that user clicks on Video Browser application. the call sequence to launch the activity is as shown in the figure.

The Activity starts its managed lifecycle with onCreate() method call. The activity comes to foreground with onRestart() call and starts interacting with the user with onStart() call.

Thanks for reading through 🙌🏼. If you found this post useful, please applaud using the 👏 button and share it through your circles.

This article was initially published as two part series (Part 1 and Part 2) on my blog ./ mult-core-dump in 2010. These articles have been cited in multiple documents including the very famous Introduction to the Android Graphics Pipeline

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