Google Cloud Messaging for Android.

This tutorial explains about that how to receive push notifications in android using GCM (Client side).
 Follow some steps here that how to do Push Notifications for android using Google Cloud Messaging:

1. First, we have to create an Google API project.
2. Install required libraries in android sdk. 
3. Create client application in android. 
4. Create one server side application to send messages to GCM server.

How GCM really works?

1. How to create an Google API project?

Follow the steps for creating new Google API project.
1. Open the Google API console page (Google account required).
The page open like this.

2. Click Create project. Your browser URL link will change something like below

   https://code.google.com/apis/console/b/0/?pli=1#project:77580014625

NOTE:
Take down the Sender-ID from your browser URL.
                                      OR
Go to Overview->Dashboard.
                                    


3. Enable the toggle Google Cloud Messaging for Android in services and accept the terms in the Terms of service page.

   4. Generate new server API key.
       a. In main page, select API Access.

        b. Click on Create new Server Key. Either a server key or a browser key should work. The advantage to using a server key is that it allows you to whitelist IP addresses. The following screen appears:

          c. Click Create.

  NOTE:
  Take down server API key (your serverApi key here). It will used in server side to send notification. New server key activate within 24 hours.

 
 2. Install Library in android SDK:

   Go to SDK Manager, Extras > Google Cloud Messaging for Android Library and install it.

If installation successful then you can find gcm directory under Your_SDK_Installed_Path/extras/google/ containing these sub-directories: gcm-client, gcm-server, samples/gcm-demo-client, samples/gcm-demo-server, and samples/gcm-demo-appengine.

Note: 
If you don't see Extras > Google Cloud Messaging for Android Library in the SDK Manager, make sure you are running version 20 or higher. Be sure to restart the SDK Manager after updating it.



3. Android GCM Application (Client Side): 

A. Copy the gcm.jar file to res->libs folder in your android project. You can find this file in Your_SDK_root\extras\google\gcm\gcm-client\dist.

B. Required permissions and changes in your android manifest file is follows.
   

     <!-- GCM works minimum version of 2.2 and maximum xx  i.e latest version. -->
    <uses-sdk
        android:minSdkVersion="8"   android:targetSdkVersion="xx" />

     <permission android:name="Your PackageName.permission.C2D_MESSAGE"           
            android:protectionLevel="signature" />
     <uses-permission android:name="Your PackageName.permission.C2D_MESSAGE" /> 
   <!--Note: the above 2 permissions is not required on 4.1 or above.-->

      <!-- App receives GCM messages. -->
      <uses-permission android:name="com.google.android.c2dm.permission.RECEIVE" />
     <!-- GCM connects to Google Services. -->
     <uses-permission android:name="android.permission.INTERNET" /> 
     <!-- GCM requires a Google account. -->
     <uses-permission android:name="android.permission.GET_ACCOUNTS" />
     <!-- Keeps the processor from sleeping when a message is received. -->
     <uses-permission android:name="android.permission.WAKE_LOCK" />
    
    <!-- BroadcastReceiver. -->
     
     <receiver android:name="com.google.android.gcm.GCMBroadcastReceiver" 
            android:permission="com.google.android.c2dm.permission.SEND" >
     <intent-filter>
     <action android:name="com.google.android.c2dm.intent.RECEIVE" />
     <action android:name="com.google.android.c2dm.intent.REGISTRATION" />
     <category android:name="Your PackageName" />
     </intent-filter>
     </receiver>
   
     <!-- Add service Intent. -->
     <service android:name=".GCMIntentService" />



C. Paste the below strings in res->values->strings.xml. If not there then create new one.


<resources>
    <string name="app_name">Prakash Creative</string>
    <string name="hello_world">Hello world!</string>
    <string name="menu_settings">Settings</string>
    <string name="title_activity_main">MainActivity</string>
    <string name="error_config">Please set the %1$s constant and recompile the app.</string>
    <string name="already_registered">Device is already registered.</string>
    <string name="gcm_registered">From GCM: device successfully registered!</string>
    <string name="gcm_unregistered">From GCM: device successfully unregistered!</string>
    <string name="gcm_message">From GCM: you got message!</string>
    <string name="gcm_error">From GCM: error (%1$s).</string>
    <string name="gcm_recoverable_error">From GCM: recoverable error (%1$s).</string>
    <string name="gcm_deleted">From GCM: server deleted %1$d pending messages!</string>
    <string name="server_registering">Trying (attempt %1$d/%2$d) to register device on Demo Server.</string>
    <string name="server_registered">From Demo Server: successfully added device!</string>
    <string name="server_unregistered">From Demo Server: successfully removed device!</string>
    <string name="server_register_error">Could not register device on Demo Server after %1$d attempts.</string>
    <string name="server_unregister_error">Could not unregister device on Demo Server (%1$s).</string>
    <string name="options_register">Register</string>
    <string name="options_unregister">Unregister</string>
    <string name="options_clear">Clear</string>
    <string name="options_exit">Exit</string>
</resources>



D. Create new class called CommonUtilities.java and add the below code.

  public final class CommonUtilities {
 
         /**
* Base URL of the Demo Server (such as http://my_host:8080/gcm-server)
         
*This link helps you to save or register your Registration-id in server. I used .net service           
           here. 
*/

static final String SERVER_URL = "http://10.0.2.2:10739/GCM-server.asmx/PostRegistration-Id";




/**
* Google API project id  is your SENDER_ID and it is use to register with GCM.
*/
static final String SENDER_ID = "77580014625";

/**
* Tag used on log messages.
*/
static final String TAG = "Prakash Creative";

/**
* Intent used to display a message in the screen.
*/
static final String DISPLAY_MESSAGE_ACTION = 

               " Your.Package.Here.DISPLAY_MESSAGE";

/**
* Intent's extra that contains the message to be displayed.
*/
static final String EXTRA_MESSAGE = "message";

/**
* Notifies UI to display a message.
* <p>
* This method is defined in the common helper because it's used both by the
* UI and the background service.
* 
* @param context
*            application's context.
* @param message
*            message to be displayed.
*/
static void displayMessage(Context context, String message) {
Intent intent = new Intent(DISPLAY_MESSAGE_ACTION);
intent.putExtra(EXTRA_MESSAGE, message);
context.sendBroadcast(intent);
}
}


E.Create a new class called  GCMIntentService. The following methods which are called by GCMBroadcastReceiver.

   

   1. onRegistered(Context context, String regId): 

         Called after a registration intent is received, passes the registration ID assigned by GCM to that     

   device/application pair as parameter. Typically, you should send the regid to your server so it can use it to   

   send messages to this device.

   2. onUnregistered(Context context, String regId):

         Called after the device has been unregistered from GCM. Typically, you should send the regid to the 

   server so it unregisters the device.

  3. onMessage(Context context, Intent intent): 

       Called when your server sends a message to GCM, and GCM delivers it to the device. If the message   

  has a payload, its contents are available as extras in the intent.

  4. onError(Context context, String errorId): 

       Called when the device tries to register or unregister, but GCM returned an error. Typically, there is    

  nothing to be done other than evaluating the error (returned by errorId) and trying to fix the problem.

  5. onRecoverableError(Context context, String errorId):

        Called when the device tries to register or unregister, but the GCM servers are unavailable. The GCM   

  library will retry the operation using exponential backup, unless this method is overridden and returns false. 

Follow the below code for GCMIntentService.java:

public class GCMIntentService extends GCMBaseIntentService{

private static final String TAG = "GCMIntentService";

   public GCMIntentService() {
       super(SENDER_ID);
   }

   @Override
   protected void onRegistered(Context context, String registrationId) {
       Log.i(TAG, "Device registered: regId = " + registrationId);
       displayMessage(context, getString(R.string.gcm_registered));
       ServerUtilities.register(context, registrationId);
   }

   @Override
   protected void onUnregistered(Context context, String registrationId) {
       Log.i(TAG, "Device unregistered");
       displayMessage(context, getString(R.string.gcm_unregistered));
       if (GCMRegistrar.isRegisteredOnServer(context)) {
           ServerUtilities.unregister(context, registrationId);
       } else {
           // This callback results from the call to unregister made on
           // ServerUtilities when the registration to the server failed.
           Log.i(TAG, "Ignoring unregister callback");
       }
   }

   @Override
   protected void onMessage(Context context, Intent intent) {
       Log.i(TAG, "Received message");
       //String message = getString(R.string.gcm_message);
       String message = intent.getStringExtra("message");
       displayMessage(context, message);
       // notifies user
       generateNotification(context, message);
   }

   @Override
   protected void onDeletedMessages(Context context, int total) {
       Log.i(TAG, "Received deleted messages notification");
       String message = getString(R.string.gcm_deleted, total);
       displayMessage(context, message);
       // notifies user
       generateNotification(context, message);
   }

   @Override
   public void onError(Context context, String errorId) {
       Log.i(TAG, "Received error: " + errorId);
       displayMessage(context, getString(R.string.gcm_error, errorId));
   }

   @Override
   protected boolean onRecoverableError(Context context, String errorId) {
       // log message
       Log.i(TAG, "Received recoverable error: " + errorId);
       displayMessage(context, getString(R.string.gcm_recoverable_error,
               errorId));
       return super.onRecoverableError(context, errorId);
   }

   /**
    * Issues a notification to inform the user that server has sent a message.
    */
   private static void generateNotification(Context context, String message) {
       int icon = R.drawable.ic_stat_gcm;
       long when = System.currentTimeMillis();
       NotificationManager notificationManager = (NotificationManager)
               context.getSystemService(Context.NOTIFICATION_SERVICE);
       Notification notification = new Notification(icon, message, when);
       String title = context.getString(R.string.app_name);
       Intent notificationIntent = new Intent(context, MainActivity.class);
       // set intent so it does not start a new activity
       notificationIntent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP |
               Intent.FLAG_ACTIVITY_SINGLE_TOP);
       PendingIntent intent =
               PendingIntent.getActivity(context, 0, notificationIntent, 0);
       notification.setLatestEventInfo(context, title, message, intent);
       notification.flags |= Notification.FLAG_AUTO_CANCEL;
       notificationManager.notify(0, notification);
   }

F. Create new class called ServerUtilities.java. This is used to register your app details in server. Follow the below code for ServerUtilities class. I have used .net web-service to save the regId in server.


public class ServerUtilities {
private static final int MAX_ATTEMPTS = 5;
       private static final int BACKOFF_MILLI_SECONDS = 1000;
       private static final Random random = new Random();

    /**
     * Register this account/device pair within the server.
     *
     * @return whether the registration succeeded or not.
     */
    static boolean register(final Context context, final String regId) {
        Log.i(TAG, "registering device (regId = " + regId + ")");
        //String serverUrl = SERVER_URL + "/register";
       
        String serverUrl = SERVER_URL;
        Map<String, String> params = new HashMap<String, String>();
        params.put("regid", regId);
        long backoff = BACKOFF_MILLI_SECONDS + random.nextInt(1000);
        // Once GCM returns a registration id, we need to register it in the
        // demo server. As the server might be down, we will retry it a couple
        // times.
        for (int i = 1; i <= MAX_ATTEMPTS; i++) {
            Log.d(TAG, "Attempt #" + i + " to register");
            try {
                displayMessage(context, context.getString(
                        R.string.server_registering, i, MAX_ATTEMPTS));
                post(serverUrl, params);
                GCMRegistrar.setRegisteredOnServer(context, true);
                String message = context.getString(R.string.server_registered);
                CommonUtilities.displayMessage(context, message);
                return true;
            } catch (IOException e) {
                // Here we are simplifying and retrying on any error; in a real
                // application, it should retry only on unrecoverable errors
             
                Log.e(TAG, "Failed to register on attempt " + i, e);
                if (i == MAX_ATTEMPTS) {
                    break;
                }
                try {
                    Log.d(TAG, "Sleeping for " + backoff + " ms before retry");
                    Thread.sleep(backoff);
                } catch (InterruptedException e1) {
                    // Activity finished before we complete - exit.
                    Log.d(TAG, "Thread interrupted: abort remaining retries!");
                    Thread.currentThread().interrupt();
                    return false;
                }
                // increase backoff exponentially
                backoff *= 2;
            }
        }
        String message = context.getString(R.string.server_register_error,
                MAX_ATTEMPTS);
        CommonUtilities.displayMessage(context, message);
        return false;
    }

    /**
     * Unregister this account/device pair within the server.
     */
    static void unregister(final Context context, final String regId) {
        Log.i(TAG, "unregistering device (regId = " + regId + ")");
        String serverUrl = SERVER_URL + "/unregister";
        Map<String, String> params = new HashMap<String, String>();
        params.put("regId", regId);
        try {
            post(serverUrl, params);
            GCMRegistrar.setRegisteredOnServer(context, false);
            String message = context.getString(R.string.server_unregistered);
            CommonUtilities.displayMessage(context, message);
        } catch (IOException e) {
            // At this point the device is unregistered from GCM, but still
            // registered in the server.
            // We could try to unregister again, but it is not necessary:
            // if the server tries to send a message to the device, it will get
            // a "NotRegistered" error message and should unregister the device.
            String message = context.getString(R.string.server_unregister_error,
                    e.getMessage());
            CommonUtilities.displayMessage(context, message);
        }
    }

    /**
     * Issue a POST request to the server.
     *
     * @param endpoint POST address.
     * @param params request parameters.
     *
     * @throws IOException propagated from POST.
     */
    private static void post(String endpoint, Map<String, String> params)
            throws IOException {
        URL url;
        try {
            url = new URL(endpoint);
        } catch (MalformedURLException e) {
            throw new IllegalArgumentException("invalid url: " + endpoint);
        }
        StringBuilder bodyBuilder = new StringBuilder();
        Iterator<Entry<String, String>> iterator = params.entrySet().iterator();
        // constructs the POST body using the parameters
        while (iterator.hasNext()) {
            Entry<String, String> param = iterator.next();
            bodyBuilder.append(param.getKey()).append('=')
                    .append(param.getValue());
            if (iterator.hasNext()) {
                bodyBuilder.append('&');
            }
        }
        String body = bodyBuilder.toString();
        Log.v(TAG, "Posting '" + body + "' to " + url);
        byte[] bytes = body.getBytes();
        HttpURLConnection conn = null;
        try {
            conn = (HttpURLConnection) url.openConnection();
            conn.setDoOutput(true);
            conn.setUseCaches(false);
            conn.setFixedLengthStreamingMode(bytes.length);
            conn.setRequestMethod("POST");
            conn.setRequestProperty("Content-Type",
                    "application/x-www-form-urlencoded;charset=UTF-8");
            // post the request
            OutputStream out = conn.getOutputStream();
            out.write(bytes);
            out.close();
            // handle the response
            int status = conn.getResponseCode();
            if (status != 200) {
              throw new IOException("Post failed with error code " + status);
            }
        } finally {
            if (conn != null) {
                conn.disconnect();
            }
        }
      }
}


G. Now its time to write code for  MainActivity. Before going to MainActivity, add the below code in res->layout->main.xml

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

    android:layout_width="fill_parent"

    android:layout_height="fill_parent" >

    <TextView

        android:id="@+id/display"

        android:layout_width="fill_parent"

        android:layout_height="wrap_content" />

</ScrollView>

Create two xml files in res->menu->
1. activity_main.xml
Please follow code for activity_main.xml...
<menu xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:id="@+id/menu_settings"
        android:title="@string/menu_settings"
        android:orderInCategory="100" />

</menu>

2. options_menu.xml

Please follow code for options_menu.xml...

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

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

    <item

        android:id="@+id/options_clear"

        android:title="@string/options_clear">

    </item>

    <item

        android:id="@+id/options_exit"

        android:title="@string/options_exit">

    </item>

</menu>

And follow the below code for MainActivity.java


public class MainActivity extends Activity {

private String TAG = "** pushAndroidActivity **";

private TextView mDisplay;

TextView RuA,paC,DEF;
TextView Defense_Tackles[];

    AsyncTask<Void, Void, Void> mRegisterTask;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        checkNotNull(SERVER_URL, "SERVER_URL");
        checkNotNull(SENDER_ID, "SENDER_ID");
        // Make sure the device has the proper dependencies.
        GCMRegistrar.checkDevice(this);
        // Make sure the manifest was properly set - comment out this line
        // while developing the app, then uncomment it when it's ready.
        GCMRegistrar.checkManifest(this);
        setContentView(R.layout.main);
        mDisplay = (TextView) findViewById(R.id.display);
        registerReceiver(mHandleMessageReceiver,
                new IntentFilter(DISPLAY_MESSAGE_ACTION));
        final String regId = GCMRegistrar.getRegistrationId(this);
        if (regId.equals("")) {
            // Automatically registers application on startup.
            GCMRegistrar.register(this, SENDER_ID);
        } else {
            // Device is already registered on GCM, check server.
            if (GCMRegistrar.isRegisteredOnServer(this)) {
                // Skips registration.
                mDisplay.append(getString(R.string.already_registered) + "\n");
            } else {
                // Try to register again, but not in the UI thread.
                // It's also necessary to cancel the thread onDestroy(),
                // hence the use of AsyncTask instead of a raw thread.
                final Context context = this;
                mRegisterTask = new AsyncTask<Void, Void, Void>() {

                    @Override
                    protected Void doInBackground(Void... params) {
                        boolean registered =
                                ServerUtilities.register(context, regId);
                        // At this point all attempts to register with the app
                        // server failed, so we need to unregister the device
                        // from GCM - the app will try to register again when
                        // it is restarted. Note that GCM will send an
                        // unregistered callback upon completion, but
                        // GCMIntentService.onUnregistered() will ignore it.
                        if (!registered) {
                            GCMRegistrar.unregister(context);
                        }
                        return null;
                    }

                    @Override
                    protected void onPostExecute(Void result) {
                        mRegisterTask = null;
                    }

                };
                mRegisterTask.execute(null, null, null);
            }
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.options_menu, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch(item.getItemId()) {
            /*
             * Typically, an application registers automatically, so options
             * below are disabled. Uncomment them if you want to manually
             * register or unregister the device (you will also need to
             * uncomment the equivalent options on options_menu.xml).
             */
            /*
            case R.id.options_register:
                GCMRegistrar.register(this, SENDER_ID);
                return true;
            case R.id.options_unregister:
                GCMRegistrar.unregister(this);
                return true;
             */
            case R.id.options_clear:
                mDisplay.setText(null);
                return true;
            case R.id.options_exit:
                finish();
                return true;
            default:
                return super.onOptionsItemSelected(item);
        }
    }

    @Override
    protected void onDestroy() {
        if (mRegisterTask != null) {
            mRegisterTask.cancel(true);
        }
        unregisterReceiver(mHandleMessageReceiver);
        GCMRegistrar.onDestroy(this);
        super.onDestroy();
    }

    private void checkNotNull(Object reference, String name) {
        if (reference == null) {
            throw new NullPointerException(
                    getString(R.string.error_config, name));
        }
    }

    private final BroadcastReceiver mHandleMessageReceiver =
            new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            String newMessage = intent.getExtras().getString(EXTRA_MESSAGE);
            mDisplay.append(newMessage + "\n");
        }
    };

NOTE: Push Notifications won't work in normal emulators. You must use Google APIs emulator and add your Google account in emulator (go to settings->Accounts & sync->Add account).

For server side example please follow link 
http://www.tejaprakash.com/2013/05/push-messages-to-gcm-server-using-net.html
You will get screen like below on successful registration.

 You will receive push notifications like below 

Download sample code from below links.