Base classes to handle GCM registration and notifications.

AndroidManifest.xml

<manifest ...>

    ...

    <uses-permission android:name="android.permission.WAKE_LOCK" />
    <permission android:name="your.package.name.permission.C2D_MESSAGE"
        android:protectionLevel="signature" />
    <uses-permission android:name="your.package.name.permission.C2D_MESSAGE" />
    <uses-permission
        android:name="com.google.android.c2dm.permission.RECEIVE" />
        
        ....
        
    <application ...>
    
        ...
        
        <receiver
            android:name="path.to.GcmBroadcastReceiver"
            android:permission="com.google.android.c2dm.permission.SEND" >
            <intent-filter>
                <!-- Receives the actual messages. -->
                <action android:name="com.google.android.c2dm.intent.RECEIVE" />
                <category android:name="your.package.name" />
            </intent-filter>
        </receiver>
        <service android:name="path.to.GcmIntentService" />
        
        ...
        
    </application>
</manifest>

GcmBroadcastReceiver.java

/*
 * Copyright 2013 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */



import android.app.Activity;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.support.v4.content.WakefulBroadcastReceiver;


/**
 * This {@code WakefulBroadcastReceiver} takes care of creating and managing a
 * partial wake lock for your app. It passes off the work of processing the GCM
 * message to an {@code IntentService}, while ensuring that the device does not
 * go back to sleep in the transition. The {@code IntentService} calls
 * {@code GcmBroadcastReceiver.completeWakefulIntent()} when it is ready to
 * release the wake lock.
 */

public class GcmBroadcastReceiver extends WakefulBroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        // Explicitly specify that GcmIntentService will handle the intent.
        ComponentName comp = new ComponentName(context.getPackageName(),
                GcmIntentService.class.getName());
        // Start the service, keeping the device awake while it is launching.
        startWakefulService(context, (intent.setComponent(comp)));
        setResultCode(Activity.RESULT_OK);
    }
}

GcmIntentService.java

/*
 * Copyright (C) 2013 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import android.app.IntentService;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.os.SystemClock;
import android.support.v4.app.NotificationCompat;
import android.util.Log;

import com.google.android.gms.gcm.GoogleCloudMessaging;

/**
 * This {@code IntentService} does the actual handling of the GCM message.
 * {@code GcmBroadcastReceiver} (a {@code WakefulBroadcastReceiver}) holds a
 * partial wake lock for this service while the service does its work. When the
 * service is finished, it calls {@code completeWakefulIntent()} to release the
 * wake lock.
 */
public class GcmIntentService extends IntentService {
    public static final int NOTIFICATION_ID = 1;
    private NotificationManager mNotificationManager;
    NotificationCompat.Builder builder;

    public GcmIntentService() {
        super("GcmIntentService");
    }
    public static final String TAG = "GCM Demo";

    @Override
    protected void onHandleIntent(Intent intent) {
        Bundle extras = intent.getExtras();
        GoogleCloudMessaging gcm = GoogleCloudMessaging.getInstance(this);
        // The getMessageType() intent parameter must be the intent you received
        // in your BroadcastReceiver.
        String messageType = gcm.getMessageType(intent);

        if (!extras.isEmpty()) {  // has effect of unparcelling Bundle
            /*
             * Filter messages based on message type. Since it is likely that GCM will be
             * extended in the future with new message types, just ignore any message types you're
             * not interested in, or that you don't recognize.
             */
            if (GoogleCloudMessaging.MESSAGE_TYPE_SEND_ERROR.equals(messageType)) {
                sendNotification("Send error: " + extras.toString());
            } else if (GoogleCloudMessaging.MESSAGE_TYPE_DELETED.equals(messageType)) {
                sendNotification("Deleted messages on server: " + extras.toString());
            // If it's a regular GCM message, do some work.
            } else if (GoogleCloudMessaging.MESSAGE_TYPE_MESSAGE.equals(messageType)) {
                // This loop represents the service doing some work.
                for (int i = 0; i < 5; i++) {
                    Log.i(TAG, "Working... " + (i + 1)
                            + "/5 @ " + SystemClock.elapsedRealtime());
                    try {
                        Thread.sleep(5000);
                    } catch (InterruptedException e) {
                    }
                }
                Log.i(TAG, "Completed work @ " + SystemClock.elapsedRealtime());
                // Post notification of received message.
                sendNotification("Received: " + extras.toString());
                Log.i(TAG, "Received: " + extras.toString());
            }
        }
        // Release the wake lock provided by the WakefulBroadcastReceiver.
        GcmBroadcastReceiver.completeWakefulIntent(intent);
    }

    // TODO: Build notficiation.
    private void sendNotification(String msg) {
        mNotificationManager = (NotificationManager)
                this.getSystemService(Context.NOTIFICATION_SERVICE);

        PendingIntent contentIntent = PendingIntent.getActivity(this, 0,
                new Intent(this, PushRegisterHelper.class), 0);

        NotificationCompat.Builder mBuilder =
                new NotificationCompat.Builder(this)
//        .setSmallIcon(R.drawable.ic_stat_gcm)
        .setContentTitle("GCM Notification")
        .setStyle(new NotificationCompat.BigTextStyle()
        .bigText(msg))
        .setContentText(msg);

        mBuilder.setContentIntent(contentIntent);
        mNotificationManager.notify(NOTIFICATION_ID, mBuilder.build());
    }
}

PushRegisterHelper.java

/*
 * Copyright 2013 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import android.content.Context;
import android.content.SharedPreferences;
import android.content.pm.PackageInfo;
import android.content.pm.PackageManager.NameNotFoundException;
import android.os.AsyncTask;
import android.util.Log;

import com.google.android.gms.common.ConnectionResult;
import com.google.android.gms.common.GooglePlayServicesUtil;
import com.google.android.gms.gcm.GoogleCloudMessaging;

import java.io.IOException;

/**
 * Helper class for registering device to GCM.
 */
public class PushRegisterHelper {

    public static final String EXTRA_MESSAGE = "message";
    public static final String PROPERTY_REG_ID = "registration_id";
    private static final String PROPERTY_APP_VERSION = "appVersion";
    private static final int PLAY_SERVICES_RESOLUTION_REQUEST = 9000;

    /**
     * Substitute you own sender ID here. This is the project number you got
     * from the API Console, as described in "Getting Started."
     */
    String SENDER_ID = "xxxxxxx";

    /**
     * Tag used on log messages.
     */
    static final String TAG = "GCM Demo";

    private OnAppRegisteredListener onAppRegisteredListener;
    private PlayServiceErrorListener playServiceErrorListener;

    private GoogleCloudMessaging gcm;
    private Context context;
    private String regid;

    public PushRegisterHelper(Context context) {
        this.context = context;
    }


    /**
     * 
     * Register device to google's GCM.
     */
    public void registerToGCM(){
        // Check device for Play Services APK. If check succeeds, proceed with GCM registration.
        if (checkPlayServices()) {
            gcm = GoogleCloudMessaging.getInstance(context);
            regid = getRegistrationId(context);
            if (regid.isEmpty()) {
                registerInBackground();
            }
        } else {
            Log.i(TAG, "No valid Google Play Services APK found.");
        }
    }

    /**
     * Check the device to make sure it has the Google Play Services APK. If
     * it doesn't, display a dialog that allows users to download the APK from
     * the Google Play Store or enable it in the device's system settings.
     */
    private boolean checkPlayServices() {
        int resultCode = GooglePlayServicesUtil.isGooglePlayServicesAvailable(context);
        if (resultCode != ConnectionResult.SUCCESS) {
            if (GooglePlayServicesUtil.isUserRecoverableError(resultCode)) {
                playServiceErrorListener.onPlayServiceError(resultCode);
                //TODO: Put this in the calling context to handle playyServiceError
                /*GooglePlayServicesUtil.getErrorDialog(resultCode, context,
                        PLAY_SERVICES_RESOLUTION_REQUEST).show();*/
            } else {
                Log.i(TAG, "This device is not supported.");
            }
            return false;
        }
        return true;
    }

    /**
     * Stores the registration ID and the app versionCode in the application's
     * {@code SharedPreferences}.
     *
     * @param context application's context.
     * @param regId registration ID
     */
    private void storeRegistrationId(Context context, String regId) {
        final SharedPreferences prefs = getGcmPreferences(context);
        int appVersion = getAppVersion(context);
        Log.i(TAG, "Saving regId on app version " + appVersion);
        SharedPreferences.Editor editor = prefs.edit();
        editor.putString(PROPERTY_REG_ID, regId);
        editor.putInt(PROPERTY_APP_VERSION, appVersion);
        editor.apply();
    }

    /**
     * Gets the current registration ID for application on GCM service, if there is one.
     * <p>
     * If result is empty, the app needs to register.
     *
     * @return registration ID, or empty string if there is no existing
     *         registration ID.
     */
    private String getRegistrationId(Context context) {
        final SharedPreferences prefs = getGcmPreferences(context);
        String registrationId = prefs.getString(PROPERTY_REG_ID, "");
        if (registrationId.isEmpty()) {
            Log.i(TAG, "Registration not found.");
            return "";
        }
        // Check if app was updated; if so, it must clear the registration ID
        // since the existing regID is not guaranteed to work with the new
        // app version.
        int registeredVersion = prefs.getInt(PROPERTY_APP_VERSION, Integer.MIN_VALUE);
        int currentVersion = getAppVersion(context);
        if (registeredVersion != currentVersion) {
            Log.i(TAG, "App version changed.");
            return "";
        }
        return registrationId;
    }

    /**
     * Registers the application with GCM servers asynchronously.
     * <p>
     * Stores the registration ID and the app versionCode in the application's
     * shared preferences.
     */
    private void registerInBackground() {
        new AsyncTask<Void, Void, String>() {
            @Override
            protected String doInBackground(Void... params) {
                String msg = "";
                try {
                    if (gcm == null) {
                        gcm = GoogleCloudMessaging.getInstance(context);
                    }
                    regid = gcm.register(SENDER_ID);
                    msg = "Device registered, registration ID=" + regid;

                    // You should send the registration ID to your server over HTTP, so it
                    // can use GCM/HTTP or CCS to send messages to your app.
                    sendRegistrationIdToBackend();

                    // For this demo: we don't need to send it because the device will send
                    // upstream messages to a server that echo back the message using the
                    // 'from' address in the message.

                    // Persist the regID - no need to register again.
                    storeRegistrationId(context, regid);
                } catch (IOException ex) {
                    msg = "Error :" + ex.getMessage();
                    // If there is an error, don't just keep trying to register.
                    // Require the user to click a button again, or perform
                    // exponential back-off.
                }
                return msg;
            }

            @Override
            protected void onPostExecute(String msg) {
                onAppRegisteredListener.onAppRegistered(regid);
            }
        }.execute(null, null, null);
    }

    /**
     * @return Application's version code from the {@code PackageManager}.
     */
    private static int getAppVersion(Context context) {
        try {
            PackageInfo packageInfo = context.getPackageManager()
                    .getPackageInfo(context.getPackageName(), 0);
            return packageInfo.versionCode;
        } catch (NameNotFoundException e) {
            // should never happen
            throw new RuntimeException("Could not get package name: " + e);
        }
    }

    /**
     * @return Application's {@code SharedPreferences}.
     */
    private SharedPreferences getGcmPreferences(Context context) {
        // This sample app persists the registration ID in shared preferences, but
        // how you store the regID in your app is up to you.
        return context.getSharedPreferences(PushRegisterHelper.class.getSimpleName(),
                Context.MODE_PRIVATE);
    }
    /**
     * Sends the registration ID to your server over HTTP, so it can use GCM/HTTP or CCS to send
     * messages to your app. Not needed for this demo since the device sends upstream messages
     * to a server that echoes back the message using the 'from' address in the message.
     */
    private void sendRegistrationIdToBackend() {
        //TODO: Register to server.
    }
    
    /**
     * 
     * Callback setters.
     * 
     */

    public void setOnAppRegisteredListener(OnAppRegisteredListener onAppRegisteredListener) {
        this.onAppRegisteredListener = onAppRegisteredListener;
    }

    public void setPlayServiceErrorListener(PlayServiceErrorListener playServiceErrorListener) {
        this.playServiceErrorListener = playServiceErrorListener;
    }

    /**
     * 
     * Callback interfaces
     * 
     */

    public interface OnAppRegisteredListener{
        public void onAppRegistered(String regId);
    }
    
    public interface PlayServiceErrorListener{
        public void onPlayServiceError(int resultcode);
    }

}