Android Middleware
Bo Pang
Bpang@cc.hut.fi
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/20
10/02/17/androidactivities-thepredominance-of-the-uithread/
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
Source: Google
• 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.
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/ShowArticl
e.asp?ArticleID=5439
• http://docs.huihoo.com/google/io/2009/Mast
ering_the_Android_Media_Framework.pdf
• http://developer.android.com/