Android Concepts

From CDOT Wiki
Jump to: navigation, search

What is Android

Android is a software product for mobile devices that has three major parts:

  1. operating system
  2. middleware
  3. applications framework

Android Architecture

Here are the major parts of the Android architecture based on definition from the Android web


Key principles

1. Linux Kernel - proven driver model, memory and process management, etc. (all the core services of a reliable operating system)

The second layer has two parts: Libraries and Android runtime.

2.1 Libraries (written in C/C++)

Component Responsibility
Surface Manager composing drawing surface onto the screen
ES & SGL core of graphics libraries
Media Framework core media: mpeg, mp3, all video formats, etc.
FreeType an engine for rendering fonts
SQLite core of data storage
WebKit an open source web browser engine
SSL security socket layer

2.2 Android Runtime

2.2.1 Core Libraries written in JAVA such as: utils, collection, i/o, etc.

2.2.2 Dalvik Virtual Machine runs dex files (bytecodes efficient for small processors)

3. Application Framework written completely in Java Programming Language

Application Functionality
Activity Manager life cycle of an application - common back stack
Package Manager keeps track the applications installed of the device
Window Manager an abstraction layer on top of surface manager
Telephony Manager Api for telephony applications
Content Providers application framework that allow applications to share data
Resource Manager used to store localized layouts, strings, bitmaps, etc.
View System building blocks of the UI, handles the event dispatcher, drawing, etc.
Notification Manager enables apps to recognize and display common alerts in the status bar

Application Building Blocks

1. Activity - a UI component that interacts with a user

2. Service - a task running in background and it does not have any UI

3. Content Provider - component that allows applications to share data with other applications.

4. Broadcast Receiver - component that responds to notification or status changes. Allows an application to register some code that will be run when it is triggered by an external event.

The basic idea in Android OS is to reuse and replace components (OSGi model).