Simple GCM

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.simplegcm">

    <permission
        android:name="com.example.simplegcm.permission.C2D_MESSAGE"
        android:protectionLevel="signature" />

    <uses-permission android:name="com.example.simplegcm.permission.C2D_MESSAGE" />
    <uses-permission android:name="android.permission.WAKE_LOCK" />

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

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

        <receiver
            android:name="com.google.android.gms.gcm.GcmReceiver"
            android:exported="true"
            android:permission="com.google.android.c2dm.permission.SEND">
            <intent-filter>
                <action android:name="com.google.android.c2dm.intent.RECEIVE" />
                <category android:name="com.example.simplegcm" />
            </intent-filter>
        </receiver>

        <service
            android:name=".MyGcmListenerService"
            android:exported="false">
            <intent-filter>
                <action android:name="com.google.android.c2dm.intent.RECEIVE" />
            </intent-filter>
        </service>

        <service
            android:name=".MyInstanceIDListenerService"
            android:exported="false">
            <intent-filter>
                <action android:name="com.google.android.gms.iid.InstanceID" />
            </intent-filter>
        </service>

        <service
            android:name=".RegistrationIntentService"
            android:exported="false">
        </service>

    </application>

</manifest>

build.gradle

// Top-level build file where you can add configuration options common to all sub-projects/modules.

dependencies {
    classpath 'com.android.tools.build:gradle:2.0.0'
    classpath 'com.google.gms:google-services:2.0.0'

    // NOTE: Do not place your application dependencies here; they belong
    // in the individual module build.gradle files
}

build.gradle (app)

// App-level build file

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    testCompile 'junit:junit:4.12'
    compile 'com.android.support:appcompat-v7:23.3.0'
    compile "com.google.android.gms:play-services-gcm:8.4.0"
}

apply plugin: 'com.google.gms.google-services'

MainActivity.java

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Intent intent = new Intent(this, RegistrationIntentService.class);
        startService(intent);
    }
}

MyGcmListenerService.java

public class MyGcmListenerService extends GcmListenerService {

    private static final String TAG = "MyGcmListenerTAG_";

    @Override
    public void onMessageReceived(String from, Bundle data) {

        String message = data.getString("message");

        Log.d(TAG, "From: " + from);
        Log.d(TAG, "Message: " + message);
    }
}

MyInstanceIDListenerService.java

public class MyInstanceIDListenerService extends InstanceIDListenerService {

    @Override
    public void onTokenRefresh() {
        Intent intent = new Intent(this, RegistrationIntentService.class);
        startService(intent);
    }
}

RegistrationIntentService.java

public class RegistrationIntentService extends IntentService {

    private static final String TAG = "RegistrationServiceTAG_";

    private static final String[] TOPICS = {"global"};

    public RegistrationIntentService() {
        super("RegistrationIntentService");
    }

    @Override
    protected void onHandleIntent(Intent intent) {
        try {
            InstanceID instanceID = InstanceID.getInstance(this);
            String token = instanceID.getToken(getString(R.string.gcm_defaultSenderId),
                    GoogleCloudMessaging.INSTANCE_ID_SCOPE, null);

            Log.i(TAG, "GCM Registration Token: " + token);

            subscribeTopics(token);

        } catch (Exception e) {
            Log.d(TAG, "Failed to complete token refresh", e);
        }
    }

    private void subscribeTopics(String token) throws IOException {
        GcmPubSub pubSub = GcmPubSub.getInstance(this);
        for (String topic : TOPICS) {
            pubSub.subscribe(token, "/topics/" + topic, null);
        }
    }
}