Carl presenting at Fom 2008 with Kieran Gutteridge

A Summary of coming articles

In this series we will seek to offer value over Google’s own very well prepared documentation by layering external developer experience and context to each of the areas we cover. This series is intended for seasoned developers who wish to gain a well documented, experienced technical insight into the platform. The following articles are planned:

Android Architecture Overview

Android is often cited as a ‘full stack’. This means that the platform is provided with an OS, sys bins/libs, JRE and SDK. The full shabang is open source from top to bottom but the documentation only lightly covers the Dalvik Virtual Machine. We explore the specifically built packages that make up android from the kernel to the Java libraries in the hope to completely orientate developers with the inner technical workings within most current Android package.

AndroidManifest.xml

The AndroidManifest.xml serves as an application’s contract between it’s end environment and the other installed applications. Through the AndroidManifest.xml an application can choose to expose its intentions, services and content to outside applications. We look into the alternative situations in which the AndroidManifest.xml’s role affects an application and expose its implementation.

Activities

An activity is embodied as a screen and breaks up high level functional elements in an Application. When navigating through an android system the forefront process operates upon the ‘context’ of the shown Activity. We examine the relationships between different types of activities in an attempt to completely understand their life cycle and how it affects the surrounding system.

Intents & BroadcasteReceivers

In Android, actions and re-actions across processes and activities are carried out through means of Intents and BroadcastReceivers. Instead of hard coding the intended application path, applications can choose to leave their journey open to re navigation and simply declare their intentions to the rest of the system. By preemptively declaring their intentions, both the user and other applications can choose to supplement any behavior upon their phone with any other piece of software that offers the same functionality. We explore the extents to which you can choose to customize the experience and look at the practical aspects and challenges that lie in deciding how to best share with the rest of the system.

Views and Resources

External resources are subject to localization and more commonly changed than the internals of an applications inner code. For this reason amongst others the layouts of views are marked up in xml. Binary resources such as images and audio files are also more prone to change and security issues and so are located within a predefined area. The Android SDK makes all resources available through an automatically generated and local binary registry. An application can easily access any of it’s resources via this registry throughout it’s operation. To what advantage has xml been used in such an unconventional why does the Android SDK choose to enforce the location of all binary files so rigidly?

Services

Services have no user interface and can run locally within an application or can take on a life of their own outside any one application, adhering to Linux’s inbuilt security model. Remote Services are shared via Android’s own IDL (Interface description language). The majority of the code for this external communication is generated for a user after declaring the interface by which the data is to be exchanged.

Content Providers

The architecture of Android applications is designed around the idea of opting into a degree of sharing within a community of applications. And application can choose to what extent it makes its data available through content providers. Content providers promote the idea of global data inter exchange and reuse within every system and we look at how Applications can best take advantage of this unique feature upon the Android platform.

We would be very happy to hear comments, criticism and requests so if you have anything to say on anything we cover then please leave a comment.

Citations & Research

• Official Google Android Overview: “Anatomy of an app”
• Google’s official videos overviews of Android Architecture:
  part 1, part 2, part 3
• Android developer reference: AndroidManifest.xml
• Android Technical Docs: android.app.Activity
  
• Android developer reference: android.content.Intent
  
• Android Technical Docs: Android.content.BroadcastReceiver
  
• Android developer reference: Security and Permissions in Android
  
• Android Technical Docs: android.view
• Android Technical Docs: android.view.View
• Types of views in Google’s view gallery
• Android Technical Docs: android.app.Service
  
• Android developer reference: Security and Permissions in Android
  
• Android Technical Docs: android.content.ContentProvider