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Android Fundamentals

Aapplications are written in the Java programming language
.apk is android package
Dalvik Executable (.dex) run by Dalvik

Each application lives in its own security sandbox
Multi-user Linux system, each application is a different user
Each application a unique Linux user ID
Each process has its own virtual machine

Application Components


Essential building blocks of an Android application
Different point through which the system can enter your application

Four different types of application components


Activities
Services
Content providers
Broadcast receivers

Activities


Represents a single screen with a user interface
Email application might have one activity that shows a list of new emails, another activity to compose an email
Different application can start any one of these activities

Services


Runs in the background
Play music in the background
Another component, such as an activity, can start the service

Content providers


Manages Shared set of application data
File system, an SQLite database, on the web
For eg: users contact information

Broadcast receivers


Responds to system-wide broadcast announcements
For eg: screen has turned off, the battery is low, or a picture was captured
No user interface but may create a status bar notification

The Manifest File
Does number of things
User permissions the application requires
Minimum API Level
Hardware and software features
API libraries the application needs

<?xml version="1.0" encoding="utf-8"?>
<manifest ... >
    <application android:icon="@drawable/app_icon.png" ... >
        <activity android:name="com.example.project.ExampleActivity"
                  android:label="@string/example_label" ... >
        </activity>
        ...
    </application>
</manifest>

Application Resources
Composed of more than just code,  images, audio files etc
animations, menus, styles, colors, layout with XML
Different language, device etc