Android Training - Part 2

Android

Android System Architecture

Source: Google

overview

• Linux Kernel: memory management, process management, networking, and other

operating system services.• Native Libraries: written in C or C++,

including: Surface Manager, 2D and 3D graphics, Media codes, SQL database, Browser engine, etc. only to be called by higher level programs

overview

• Android Runtime: including the Dalvik virtual machine and the core Java libraries. (not J2SE/J2ME)

• Application Framework: Activity manager, Content providers, Resource manager, Notification manager

• Applications and Widgets: the real programs display information and interact with users.

Media Framework

• Android use OpenCore as core component of Media framework

• OpenCore supports MP3, AAC, AAC+, 3GPP, MPEG-4 and JPEG,

Media Framework

Media Framework

• Example: • MediaPlayer mp = new MediaPlayer(); • mp.setDataSource(PATH_TO_FILE); • mp.prepare(); • mp.start();

Media Framework

• OpenCore lib has a C/S Architecture.• MediaPlayer invoke JNI to manipulate client.• The client request to the server to control

hardwares.

Media Framework

Media Framework

Activity Manager

• each user interface screen is represented by an Activity class.

• Each activity has its own life cycle.• Activity uses Intent object to jump between

them.

Life cycle of activity

Source: Hello Adroid

Intent and Intent filters

• Intent activates activities, services, and broadcast receivers.

• Intent can be used in explicit way or implicit way.

• The implicit way depends on parameters: Action, Data(url and MIME type) , Category

Intent and Intent filters

• To receive other components' request, components’ need to register filters at activities framework.

• When launch a intent object, framework will match and find the qualified components and leave them for users to choose which to run.

Intent and Intent filters• Example• <intent-filter>

<action android:name="android.intent.action.VIEW" /> <action android:name="android.intent.action.EDIT" /> <action android:name="android.intent.action.PICK" /> <category android:name="android.intent.category.DEFAULT" /> <data android:mimeType="vnd.android.cursor.dir/vnd.google.note" /> </intent-filter>

Activities and Tasks

• A task is a stack which contain several activities share the same affinity.

Source: http://blog.akquinet.de/2010/02/17/android-activities-the-predominance-of-the-ui-thread/

Activities and Tasks

• There are four different launch modes that can be assigned to an <activity> element's launchMode attribute:

• "standard" (the default mode) "singleTop" "singleTask" "singleInstance"

• First two share the same affinity with application, the others don’t.

Content manager

• Manage data• Client+server architecture. • Content Resolver provides API interface for

applications.• Content Providers is the server managing the

DB tables and database content with different application.

Content manager• URI identifies the data or the table

• A: Standard prefix indicating that the data is controlled by a content provider.

• B: The authority part of the URI; it identifies the content provider.

• C: The path that the content provider uses to determine what kind of data is being requested.

• D: The ID of the specific record being requested.

Source: Google

Service Lifecycle

Security and permissions

• security between applications and the system is enforced at the process level through standard Linux facilities

• Application can't disrupt other applications, except by explicitly declaring the permissions it

• Each Android package is given its own unique Linux user ID

References

• http://www.j2medev.com/android/ShowArticle.asp?ArticleID=5439

• http://docs.huihoo.com/google/io/2009/Mastering_the_Android_Media_Framework.pdf

• http://developer.android.com/