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Push Notification:

Push Notification allows an application to listen for messages being ‘pushed’ to it from the server.
Through Push Notification, our apps can provide uses even when they aren’t running.

Different techniques that could be used for push notifications in android:

1)  Polling:  In this technique device is polling the server on a regular basis to see if there is anything there.

Polling that heavily just to check for notification is not a good idea,that would hurt battery life pretty badly after not too long.

2)  Creating a service: In this technique service create a persistent connection to your server.
This will also drain the phone’s battery and it will create problem on server side also if you had more users

3)  SMS: In this method clients gets notified by SMS.

This technique is better as compare to other techniques because:

1) Transfer content as soon as available
2) Save device battery
3) Reduce data traffic for user

Way to implement push via SMS:

1) Your application should add permission in manifest :
Permission:  <uses-permission android:name=”android.permission.RECEIVE_SMS” />
2) and Registers a BroadcastReceiver, either in the manifest XML or in Java, and will get control when the events occur.
<receiver android:name=”.ReceiverClass”>
<intent-filter>
<action android:name=”android.provider.Telephony.SMS_RECEIVED” />
</intent-filter>
</receiver>
3) SMS Header may contain “app port” field that is dedicated range of free usable port numbers.Port handling not yet supported in Android 1.6.
4) You’d have to parse the PDU and get the port from there manually, you can listen to all SMS messages, parse the PDU of each incoming message and see if the destination port
matches the one that you are expecting. But so can other apps.so there’s no way to ensure that just one specific app gets to know about an incoming SMS to a specific port.
5) After matching ports appliaction can handle notification with the help of notification manager.
The problem with this method is that Android currently has no way to cancel the notification that is sent by the messaging app.So for every notification your app gets, the OS will also show a text message.

What is the Android NDK?

The Android NDK is a companion tool used only in conjunction with Android SDK which allows application developers to build performance-critical portions of their apps by use of native (C/C++) code.

This provide benefits in form of reuse of existing code and increased speed.

Contents of NDK:

• A set of tools and build files for generating native code libraries from C and C++ sources.
• A way to embed the corresponding native libraries into application package files (.apks) that can be deployed on Android devices.
• A set of native system headers and libraries supported starting from Android 1.5 .
• Documentation, samples, and tutorials.

Download NDK from http://developer.android.com/sdk/ndk/1.6_r1/index.html and uncompress it.Now run the script in <NDK>/build/host-setup.sh.This creates <NDK>/out/host/config.mk which configure NDK for system.

How to write an application using NDK?

Follow underneath steps to create our own application using NDK and make it running on emulator.

Write an Android Activity

You need to include following lines of extra code in our java file.

• Call native method inside on create method.
• Declare native method outside oncreate method.
• Call to “System.loadLibrary” method inside a static initializer block to load our shared library object.

package com.example.FileLoaderActivity;

public class FileLoaderActivity extends Activity {

private static String TAG = “FileLoaderActivity”;

// The name of a test file to write

private static String FILENAME = “hello”;

// The full path to the test file

private static String PATH = “/data/data/com.example.FileLoaderActivity/” + FILENAME;

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

……………

// Call the native method to read the file just written

byte[] bytes = loadFile(PATH);

…………..

}

public native byte[] loadFile(String fileName); static {

System.loadLibrary(“fileloader”);

}

}

Generating C/C++ header files For generating C/C++ header file for our shared library:

• Build project which generates Java.class files under <project_home>/bin
• Use javah tool to generate a C/C++ header file.

Issue the following command at the top of <project_home>, my command looks like:

javah -o fileloader.h -classpath bin com.example.FileLoaderActivity.FileLoaderActivity

The above command will generate a file called fileloader.h .

Creating our Shared Library

Create two folders which will contain source code and make files:

• mkdir -p ~/workspace/<project_home>/jni folder – contain the source code for our shared library.
• mkdir -p $NDK_HOME/apps/fileloader folder- “project definition” folder for our shared library

Now copy header file ‘hellondk.h’ from Eclipse project folder to ~/workspace/<project_home>/jni/

For building our NDK project, we need to create two Makefiles which will specify how and from where to pick source code and library file.

• Android.mk
• Application.mk

“~/workspace/<project_home>/jni/Android.mk”

Android.mk file describes source file to build system and its contents are :

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE := fileloader

LOCAL_SRC_FILES := fileloader.c

LOCAL_LDLIBS := -L$(SYSROOT)/usr/lib -llog

include $(BUILD_SHARED_LIBRARY)

“$NDK_HOME/apps/fileloader/Application.mk“

Application.mk file describes modules that are needed by your application and it looks like:

APP_PROJECT_PATH := ~/workspace/FileLoaderActivity

APP_MODULES := fileloader

Creating Shared Library Source

Now create C source file for shared library which defines JNI method called by Java file.Signature of this Jni method should match with fileloader.h file generated by eclipse build system.

~/workspace/FileLoaderActivity/jni/fileloader.c

jbyteArray Java_com_example_FileLoaderActivity_FileLoaderActivity_loadFile

(JNIEnv* env, jobject thiz, jstring filename)

{

……………………..

}

Compiling our Shared Library

Change current working directory to $NDK_HOME and run command “make APP=fileloader”.You can find your shared library into folder $NDK_HOME/out/apps/fileloader/ directory.You can now run our FileLoaderActivity project from within Eclipse. Dont forget to push file “hello” mentioned in java code before running project.Here’s a screenshot of what you should see in the emulator.