Android Application Fundamentals

•  Android applications are written in the Java programming language.
• The Android SDK tools compile the code—along with any data and resource files—into an Android package, an archive file with an .apk suffix.
• By using the aapt tool, the data and resources bundled into a package.
•   aapt- android asset packaging tool.
• apk- android package kit.
• The .apk file is used to install the applications on Android-powered devices.
• Each Android application lives in its own world:
•  By default, every application runs in its own Linux process.
• Android starts the process when any of the application's code needs to be executed, and shuts down the process when it's no longer needed or when some system resources are required by other applications.
•  Each process has its own virtual machine (VM), so application code runs in isolation from the code of all other applications.
•  By default, each application is assigned a unique Linux user ID.
• Permissions are set so that the application's files are visible only to that user, and to the application itself.
• There are ways to export them to other applications as well:
• It's possible to arrange for two applications to share the same user ID, in which case they will be able to see each other's files.
• To conserve system resources, applications with the same ID can also arrange to run in the same Linux process, sharing the same VM.
• An application can request permission to access device data such as the user's contacts, SMS messages, the mountable storage (SD card), camera, Bluetooth, and more. All application permissions must be granted by the user at install time.

Location Based Services in Android

Location Based Services

•   Android gives our applications access to the location services through the classes in the android.location package.
•  We can utilize GPS and Android’s Network Location Provider to acquire the user location.
•   GPS provider:
•  GPS is most accurate.
•  It works only outdoors.
•  Quickly consumes battery power.
•  Doesn't return the location as quickly as user want.
•  Network Location Provider:
•  Determines the user location using the cell-tower and Wi-Fi signals.
• It works indoors and outdoors.
• Responds faster.
• It uses less battery.
• To obtain the user location we can use both GPS and Network Location Provider or just one.
• Key classes:
• LocationManager.
• LocationProvider.
• LcoationManager provides access to the system location services. This is done through getSystemService.
• Using LocationManager class we can obtain periodic updates of the locations.
• We can request location updates of devices using requestLocationUpdates() method. This method takes four parameters:
•  Provider - The name of the location provider you wish to use.
• minTime - The minimum time interval for notifications, in milliseconds.
•  minDistance - The minimum distance interval for notifications, in meters.
• listener - An object whose onLocationChanged() method will be called for each location update.
•  In order to receive location updates we must request user permissions.
•    NETWORK_PROVIDER – android.permission.ACCESS_COARSE_LOCATION.
• GPS_PROVIDER -  android.permission.ACCESS_FINE_LOCATION.
• The following statement should be added to the AndroidManifest.xml
• < uses-permission android:name=”android.permission.ACCESS_FINE_LOCATION” />
• If we are using both NETWORK_PROVIDER and GPS_PROVIDER, then we need to request only the ACCESS_FINE_LOCATION permission, because it includes permission for both providers.
•   Using DDMS we can simulate location data in several ways through Emulator Controls. They are as follows:
• Manually send individual longitude/latitude coordinates to the device.
• Use a GPX file describing a route for playback to the device.
• Use a KML file describing individual place marks for sequenced playback to the device.
• To send location data through DDMS we must be sure that a device selected in the Devices panel. (Available from Window > Show View > Other > Devices).

Ø  Example:

Main.xml:

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:orientation="vertical"

    android:layout_width="fill_parent"

    android:layout_height="fill_parent"

    >

<TextView 

    android:layout_width="fill_parent"

    android:layout_height="wrap_content"

    android:text="@string/hello"

    />

    <Button

       android:id="@+id/retrieve_location_button"

       android:text="Get Location"

       android:layout_width="wrap_content"

       android:layout_height="wrap_content"

       />

</LinearLayout>

GeoCoderActivity.java:

          package com.snigdha.android;

import android.app.Activity;

import android.content.Context;

import android.location.Location;

import android.location.LocationListener;

import android.location.LocationManager;

import android.os.Bundle;

import android.view.View;

import android.view.View.OnClickListener;

import android.widget.Button;

import android.widget.Toast;

public class GeoCoderExampleActivity extends Activity {

    /** Called when the activity is first created. */

private static final long MINIMUM_DISTANCE_CHANGE_FOR_UPDATES = 1;

    private static final long MINIMUM_TIME_BETWEEN_UPDATES = 1000;

    protected LocationManager locationManager;

   protected Button retrieveLocationButton;

    public void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

       setContentView(R.layout.main);

 retrieveLocationButton = (Button) findViewById(R.id.retrieve_location_button);

 locationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);

locationManager.requestLocationUpdates( LocationManager.GPS_PROVIDER,                              MINIMUM_TIME_BETWEEN_UPDATES,MINIMUM_DISTANCE_CHANGE_FOR_UPDATES,

                                   new MyLocationListener()   );

   retrieveLocationButton.setOnClickListener(new OnClickListener() {

public void onClick(View v) { showCurrentLocation();

                               }

                       });                              

                       }  

   protected void showCurrentLocation() {

   Location location = locationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);

    if (location != null) {

  String message = String.format( "Current Location \n Longitude: %1$s \n Latitude: %2$s",   location.getLongitude(), location.getLatitude()   );

   Toast.makeText(GeoCoderExampleActivity.this, message,                    Toast.LENGTH_LONG).show();

                  }

              } 

   private class MyLocationListener implements LocationListener {

       public void onLocationChanged(Location location) {

    String message = String.format( "New Location \n Longitude: %1$s \n Latitude: 2$s",   location.getLongitude(), location.getLatitude()       );

 Toast.makeText(GeoCoderExampleActivity.this, message, oast.LENGTH_LONG).show();

                           }

      public void onStatusChanged(String s, int i, Bundle b) {

Toast.makeText(GeoCoderExampleActivity.this, "Provider status changed",

                                       Toast.LENGTH_LONG).show();

                           }

 public void onProviderDisabled(String s) {

Toast.makeText(GeoCoderExampleActivity.this, "Provider disabled by the user. GPS turned off", Toast.LENGTH_LONG).show();

        }

 public void onProviderEnabled(String s) {                        Toast.makeText(GeoCoderExampleActivity.this, "Provider enabled by the user. GPS turned on", Toast.LENGTH_LONG).show();

                           }

}

}

AndroidManifest.xml:

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

      package="com.snigdha.android"

      android:versionCode="1"

      android:versionName="1.0">

    <uses-sdk android:minSdkVersion="8" />

   

    <uses-permission  android:name="android.permission.INTERNET"/>

<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />

<uses-permission android:name="android.permission.ACCESS_MOCK_LOCATION" /> <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>

 <application android:icon="@drawable/icon" android:label="@string/app_name">

<activity android:name=".GeoCoderExampleActivity"

                  android:label="@string/app_name">

      <intent-filter>

            <action android:name="android.intent.action.MAIN" />

      <category android:name="android.intent.category.LAUNCHER" />

      </intent-filter>

        </activity>

    </application>                                     

</manifest>

Screen Shots:

Figure-1                                                    

Figure - 2

Figure - 4

Figure - 3

                                                                                                                                                

•  Figure-2 displaying the current location data retrieved by the provider.
• Figure-3 and Figure -4 showing a toast messages when the GPS is disabled and enabled by the user.

Architecture of Android

Android Architecture

·                The following diagram shows the various layers that make up the Android operating system (OS).

                                                Architecture of Android Operating System

·          Linux Kernel:

Ø  Android relies on Linux version 2.6 for core system services such as security, memory management, process management, network stack, and driver model.

Ø  The kernel also acts as an abstraction layer between the hardware and the rest of the software stack.

·          Android Runtime:

Ø  Core Libraries: Android includes a set of core libraries that provides most of the functionality available in the core libraries of the Java programming language.

Ø  Dalvik Virtual machine:

üEvery Android application runs in its own process, with its own instance of the Dalvik virtual machine.

üDalvik has been written so that a device can run multiple VMs efficiently. The Dalvik VM executes files in the Dalvik Executable (.dex) format which is optimized for minimal memory footprint.

üThe VM is register-based, and runs classes compiled by a Java language compiler that have been transformed into the .dex format by the included "dx" tool.

üThe Dalvik VM relies on the Linux kernel for underlying functionality such as threading and low-level memory management.

·         Libraries:

Ø  Android includes a set of C/C++ libraries used by various components of the Android system. These capabilities are exposed to developers through the Android application framework. Some of the core libraries are listed below:

ü  System C library - a BSD-derived implementation of the standard C system library (libc), tuned for embedded Linux-based devices

ü  Media Libraries - based on PacketVideo's OpenCORE; the libraries support playback and recording of many popular audio and video formats, as well as static image files, including MPEG4, H.264, MP3, AAC, AMR, JPG, and PNG

ü  Surface Manager - manages access to the display subsystem and seamlessly composites 2D and 3D graphic layers from multiple applications

ü  LibWebCore - a modern web browser engine which powers both the Android browser and an embeddable web view

ü  SGL - the underlying 2D graphics engine

ü  3D libraries - an implementation based on OpenGL ES 1.0 APIs; the libraries use either hardware 3D acceleration (where available) or the included, highly optimized 3D software rasterizer

ü  FreeType - bitmap and vector font rendering

ü  SQLite - a powerful and lightweight relational database engine available to all applications

·         Application Framework:

Ø   Android offers developers the ability to build extremely rich and innovative applications.

Ø   Developers are free to take advantage of the device hardware, access location information, run background services, set alarms, add notifications to the status bar, and much, much more.

Ø  Full access to the same framework APIs used by the core applications.

Ø  The application architecture is designed to simplify the reuse of components; any application can publish its capabilities and any other application may then make use of those capabilities.

Platform Services Activity Manager	Hardware Services Telephony Service
Package Manager	Bluetooth Service
Window Manager	Wi-Fi Service
Resource Manager	USB Service
Content Providers	Sensor Service
View System

 Applications:

Ø  Applications are the general applications that are pre shipped with the phone or downloaded and installed from the market.

Example:

§  A set of core applications including an email client, SMS program, calendar, maps, browser, contacts, and others.

Ø  All applications are written using the Java programming language.

Ø  Applications make use of Application Framework.