Sending push notifications to Android with Azure Notification Hubs

2016-7-5 18 minutes to read Contributors

Overview

Important

This topic demonstrates push notifications with Google Cloud Messaging (GCM). If you are using Google's Firebase Cloud Messaging (FCM), see Sending push notifications to Android with Azure Notification Hubs and FCM.

This tutorial shows you how to use Azure Notification Hubs to send push notifications to an Android application. You'll create a blank Android app that receives push notifications by using Google Cloud Messaging (GCM).

The goal of this article is to help you get started using Azure Notification Hubs as quickly as possible. The article presents a very simple broadcast scenario that focuses on the basic concepts of Notification Hubs.

If you are already familiar with Notification Hubs, you might want to select another topic from the left navigation or go to the relevant articles in the "Next steps" section.

We take your feedback seriously. If you have any difficulty completing this topic, or if you have recommendations for improving this content, we invite you to provide feedback at the end of the article.

The completed code for this tutorial can be downloaded from GitHub here.

Prerequisites

Important

To complete this tutorial, you must have an active Azure account. If you don't have an account, you can create a free trial account in just a couple of minutes. For details, see Azure Free Trial.

In addition to an active Azure account mentioned above, this tutorial only requires the latest version of Android Studio.

Completing this tutorial is a prerequisite for all other Notification Hubs tutorials for Android apps.

Creating a project that supports Google Cloud Messaging

Navigate to the Google Cloud Console, sign in with your Google account credentials.
Click Create Project, type a project name, then click Create. If requested, carry out the SMS Verification, and click Create again.

Type in your new Project name and click Create project.
Click the Utilities and More button and then click Project Information. Make a note of the Project Number. You will need to set this value as the SenderId variable in the client app.
In the project dashboard, under Mobile APIs, click Google Cloud Messaging, then on the next page click Enable API and accept the terms of service.
In the project dashboard, Click Credentials > Create Credential > API Key.
In Create a new key, click Server key, type a name for your key, then click Create.
Make a note of the API KEY value.

You will use this API key value to enable Azure to authenticate with GCM and send push notifications on behalf of your app.

Configure a new notification hub

Sign in to the Azure portal.
Select New > Web + Mobile > Notification Hub.
In the Notification Hub box, type a unique name. Select your Region, Subscription, and Resource Group (if you have one already).

If you already have a service bus namespace that you want to create the hub in, do the following:

a. In the Namespace area, select the Select Existing link.

b. Select Create.

If you don't already have a service bus namespace, you can use the default name, which is created based on the hub name (if the namespace name is available).

After you've created the namespace and notification hub, the Azure portal opens.
Select Settings > Access Policies. Note the two connection strings that are available to you. You will need them to handle push notifications later.

6. In the Settings blade, select Notification Services and then Google (GCM). Enter the API key and click Save.

Azure Notification Hubs - Google (GCM)

Your notification hub is now configured to work with GCM, and you have the connection strings to both register your app to receive and send push notifications.

Connect your app to the notification hub

Create a new Android project

In Android Studio, start a new Android Studio project.
Choose the Phone and Tablet form factor and the Minimum SDK that you want to support. Then click Next.
Choose Empty Activity for the main activity, click Next, and then click Finish.

Add Google Play services to the project

Open the Android SDK Manager by clicking the icon on the toolbar of Android Studio or by clicking Tools -> Android -> SDK Manager on the menu. Locate the target version of the Android SDK that is used in your project , open it by clicking Show Package Details, and choose Google APIs, if it is not already installed.
Click the SDK Tools tab. If you haven't already installed Google Play Service, click Google Play Services as shown below. Then click Apply to install.

Note the SDK path, for use in a later step.
Open the build.gradle file in the app directory.

Add this line under dependencies:

    compile 'com.google.android.gms:play-services-gcm:9.2.0'

Click the Sync Project with Gradle Files icon in the tool bar.

Open AndroidManifest.xml and add this tag to the application tag.

 <meta-data android:name="com.google.android.gms.version"
     android:value="@integer/google_play_services_version" />

Adding Azure Notification Hubs libraries

In the Build.Gradle file for the app, add the following lines in the dependencies section.

 compile 'com.microsoft.azure:notification-hubs-android-sdk:0.4@aar'
 compile 'com.microsoft.azure:azure-notifications-handler:1.0.1@aar'

Add the following repository after the dependencies section.

 repositories {
     maven {
         url "http://dl.bintray.com/microsoftazuremobile/SDK"
     }
 }

Updating the AndroidManifest.xml.

To support GCM, we must implement a Instance ID listener service in our code which is used to obtain registration tokens using Google's Instance ID API. In this tutorial we will name the class MyInstanceIDService.

Add the following service definition to the AndroidManifest.xml file, inside the <application> tag. Replace the <your package> placeholder with the your actual package name shown at the top of the AndroidManifest.xml file.
```
 <service android:name="<your package>.MyInstanceIDService" android:exported="false">
     <intent-filter>
         <action android:name="com.google.android.gms.iid.InstanceID"/>
     </intent-filter>
 </service>
```
Once we have received our GCM registration token from the Instance ID API, we will use it to register with the Azure Notification Hub. We will support this registration in the background using an IntentService named RegistrationIntentService. This service will also be responsible for refreshing our GCM registration token.

Add the following service definition to the AndroidManifest.xml file, inside the <application> tag. Replace the <your package> placeholder with the your actual package name shown at the top of the AndroidManifest.xml file.
```
 <service
     android:name="<your package>.RegistrationIntentService"
     android:exported="false">
 </service>
```

We will also define a receiver to receive notifications. Add the following receiver definition to the AndroidManifest.xml file, inside the <application> tag. Replace the <your package> placeholder with the your actual package name shown at the top of the AndroidManifest.xml file.

 <receiver android:name="com.microsoft.windowsazure.notifications.NotificationsBroadcastReceiver"
     android:permission="com.google.android.c2dm.permission.SEND">
     <intent-filter>
         <action android:name="com.google.android.c2dm.intent.RECEIVE" />
         <category android:name="<your package name>" />
     </intent-filter>
 </receiver>

Add the following necessary GCM related permissions below the </application> tag. Make sure to replace <your package> with the package name shown at the top of the AndroidManifest.xml file.

For more information on these permissions, see Setup a GCM Client app for Android.

 <uses-permission android:name="android.permission.INTERNET"/>
 <uses-permission android:name="android.permission.GET_ACCOUNTS"/>
 <uses-permission android:name="android.permission.WAKE_LOCK"/>
 <uses-permission android:name="com.google.android.c2dm.permission.RECEIVE" />

 <permission android:name="<your package>.permission.C2D_MESSAGE" android:protectionLevel="signature" />
 <uses-permission android:name="<your package>.permission.C2D_MESSAGE"/>

Adding code

In the Project View, expand app > src > main > java. Right-click your package folder under java, click New, and then click Java Class. Add a new class named NotificationSettings.

Make sure to update the these three placeholders in the following code for the NotificationSettings class:
- SenderId: The project number you obtained earlier in the Google Cloud Console.
- HubListenConnectionString: The DefaultListenAccessSignature connection string for your hub. You can copy that connection string by clicking Access Policies on the Settings blade of your hub on the Azure Portal.
- HubName: Use the name of your notification hub that appears in the hub blade in the Azure Portal.
  
  NotificationSettings code:
  
  public class NotificationSettings {
```
  public static String SenderId = "<Your project number>";
  public static String HubName = "<Your HubName>";
  public static String HubListenConnectionString = "<Your default listen connection string>";
```
  }

Using the steps above, add another new class named MyInstanceIDService. This will be our Instance ID listener service implementation.

The code for this class will call our IntentService to refresh the GCM token in the background.

 import android.content.Intent;
 import android.util.Log;
 import com.google.android.gms.iid.InstanceIDListenerService;

 public class MyInstanceIDService extends InstanceIDListenerService {

     private static final String TAG = "MyInstanceIDService";

     @Override
     public void onTokenRefresh() {

         Log.i(TAG, "Refreshing GCM Registration Token");

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

Add another new class to your project named, RegistrationIntentService. This will be the implementation for our IntentService that will handle refreshing the GCM token and registering with the notification hub.

Use the following code for this class.

 import android.app.IntentService;
 import android.content.Intent;
 import android.content.SharedPreferences;
 import android.preference.PreferenceManager;
 import android.util.Log;

 import com.google.android.gms.gcm.GoogleCloudMessaging;
 import com.google.android.gms.iid.InstanceID;
 import com.microsoft.windowsazure.messaging.NotificationHub;

 public class RegistrationIntentService extends IntentService {

     private static final String TAG = "RegIntentService";

     private NotificationHub hub;

     public RegistrationIntentService() {
         super(TAG);
     }

     @Override
     protected void onHandleIntent(Intent intent) {        
         SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
         String resultString = null;
         String regID = null;

         try {
             InstanceID instanceID = InstanceID.getInstance(this);
             String token = instanceID.getToken(NotificationSettings.SenderId,
                     GoogleCloudMessaging.INSTANCE_ID_SCOPE);        
             Log.i(TAG, "Got GCM Registration Token: " + token);

             // Storing the registration id that indicates whether the generated token has been
             // sent to your server. If it is not stored, send the token to your server,
             // otherwise your server should have already received the token.
             if ((regID=sharedPreferences.getString("registrationID", null)) == null) {        
                 NotificationHub hub = new NotificationHub(NotificationSettings.HubName,
                         NotificationSettings.HubListenConnectionString, this);
                 Log.i(TAG, "Attempting to register with NH using token : " + token);

                 regID = hub.register(token).getRegistrationId();

                 // If you want to use tags...
                 // Refer to : https://azure.microsoft.com/en-us/documentation/articles/notification-hubs-routing-tag-expressions/
                 // regID = hub.register(token, "tag1", "tag2").getRegistrationId();

                 resultString = "Registered Successfully - RegId : " + regID;
                 Log.i(TAG, resultString);        
                 sharedPreferences.edit().putString("registrationID", regID ).apply();
             } else {
                 resultString = "Previously Registered Successfully - RegId : " + regID;
             }
         } catch (Exception e) {
             Log.e(TAG, resultString="Failed to complete token refresh", e);
             // If an exception happens while fetching the new token or updating our registration data
             // on a third-party server, this ensures that we'll attempt the update at a later time.
         }

         // Notify UI that registration has completed.
         if (MainActivity.isVisible) {
             MainActivity.mainActivity.ToastNotify(resultString);
         }
     }
 }

In your MainActivity class, add the following import statements above the class declaration.

 import com.google.android.gms.common.ConnectionResult;
 import com.google.android.gms.common.GoogleApiAvailability;
 import com.google.android.gms.gcm.*;
 import com.microsoft.windowsazure.notifications.NotificationsManager;
 import android.util.Log;
 import android.widget.TextView;
 import android.widget.Toast;

Add the following private members at the top of the class. We will use these check the availability of Google Play Services as recommended by Google.

 public static MainActivity mainActivity;
 public static Boolean isVisible = false;    
 private GoogleCloudMessaging gcm;
 private static final int PLAY_SERVICES_RESOLUTION_REQUEST = 9000;

In your MainActivity class, add the following method to the availability of Google Play Services.

 /**
  * 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() {
     GoogleApiAvailability apiAvailability = GoogleApiAvailability.getInstance();
     int resultCode = apiAvailability.isGooglePlayServicesAvailable(this);
     if (resultCode != ConnectionResult.SUCCESS) {
         if (apiAvailability.isUserResolvableError(resultCode)) {
             apiAvailability.getErrorDialog(this, resultCode, PLAY_SERVICES_RESOLUTION_REQUEST)
                     .show();
         } else {
             Log.i(TAG, "This device is not supported by Google Play Services.");
             ToastNotify("This device is not supported by Google Play Services.");
             finish();
         }
         return false;
     }
     return true;
 }

In your MainActivity class, add the following code that will check for Google Play Services before calling your IntentService to get your GCM registration token and register with your notification hub.

 public void registerWithNotificationHubs()
 {
     Log.i(TAG, " Registering with Notification Hubs");

     if (checkPlayServices()) {
         // Start IntentService to register this application with GCM.
         Intent intent = new Intent(this, RegistrationIntentService.class);
         startService(intent);
     }
 }

In the OnCreate method of the MainActivity class, add the following code to start the registration process when activity is created.

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

     mainActivity = this;
     NotificationsManager.handleNotifications(this, NotificationSettings.SenderId, MyHandler.class);
     registerWithNotificationHubs();
 }

Add these additional methods to the MainActivity to verify app state and report status in your app.

 @Override
 protected void onStart() {
     super.onStart();
     isVisible = true;
 }

 @Override
 protected void onPause() {
     super.onPause();
     isVisible = false;
 }

 @Override
 protected void onResume() {
     super.onResume();
     isVisible = true;
 }

 @Override
 protected void onStop() {
     super.onStop();
     isVisible = false;
 }

 public void ToastNotify(final String notificationMessage) {
     runOnUiThread(new Runnable() {
         @Override
         public void run() {
             Toast.makeText(MainActivity.this, notificationMessage, Toast.LENGTH_LONG).show();
             TextView helloText = (TextView) findViewById(R.id.text_hello);
             helloText.setText(notificationMessage);
         }
     });
 }

The ToastNotify method uses the "Hello World" TextView control to report status and notifications persistently in the app. In your activity_main.xml layout, add the following id for that control.
```
android:id="@+id/text_hello"
```
Next we will add a subclass for our receiver we defined in the AndroidManifest.xml. Add another new class to your project named MyHandler.

Add the following import statements at the top of MyHandler.java:

import android.app.NotificationManager;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.NotificationCompat;
import com.microsoft.windowsazure.notifications.NotificationsHandler;

Add the following code for the MyHandler class making it a subclass of com.microsoft.windowsazure.notifications.NotificationsHandler.

This code overrides the OnReceive method, so the handler will report notifications that are received. The handler also sends the push notification to the Android notification manager by using the sendNotification() method. The sendNotification() method should be executed when the app is not running and a notification is received.

public class MyHandler extends NotificationsHandler {
    public static final int NOTIFICATION_ID = 1;
    private NotificationManager mNotificationManager;
    NotificationCompat.Builder builder;
    Context ctx;

    @Override
    public void onReceive(Context context, Bundle bundle) {
        ctx = context;
        String nhMessage = bundle.getString("message");
        sendNotification(nhMessage);
        if (MainActivity.isVisible) {
            MainActivity.mainActivity.ToastNotify(nhMessage);
        }
    }

    private void sendNotification(String msg) {

        Intent intent = new Intent(ctx, MainActivity.class);
        intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);

        mNotificationManager = (NotificationManager)
                ctx.getSystemService(Context.NOTIFICATION_SERVICE);

        PendingIntent contentIntent = PendingIntent.getActivity(ctx, 0,
                intent, PendingIntent.FLAG_ONE_SHOT);

        Uri defaultSoundUri = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);
        NotificationCompat.Builder mBuilder =
                new NotificationCompat.Builder(ctx)
                        .setSmallIcon(R.mipmap.ic_launcher)
                        .setContentTitle("Notification Hub Demo")
                        .setStyle(new NotificationCompat.BigTextStyle()
                                .bigText(msg))
                        .setSound(defaultSoundUri)
                        .setContentText(msg);

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

In Android Studio on the menu bar, click Build > Rebuild Project to make sure that no errors are present in your code.

Sending push notifications

You can test receiving push notifications in your app by sending them via the Azure Portal - look for the Troubleshooting Section in the hub blade, as shown below.

Azure Notification Hubs - Test Send

Push notifications are normally sent in a back-end service like Mobile Apps or ASP.NET using a compatible library. You can also use the REST API directly to send notification messages if a library is not available for your back-end.

Here is a list of some other tutorials you may want to review for sending notifications:

Azure Mobile Apps : For an example of how to send notifications from an Mobile Apps backend integrated with Notification Hubs, see Add Push Notifications to your iOS App.
ASP.NET : Use Notification Hubs to push notifications to users.
Azure Notification Hub Java SDK: See How to use Notification Hubs from Java for sending notifications from Java. This has been tested in Eclipse for Android Development.
PHP: How to use Notification Hubs from PHP.

In the next section of the tutorial, you will learn how to use the Notification Hub REST interface to send the notification message directly in your app. All registered devices receive the notification sent by any device.

(Optional) Send push notifications directly from the app

Normally, you would send notifications using a backend server. For some cases, you might want to be able to send push notifications directly from the client application. This section explains how to send notifications from the client using the Azure Notification Hub REST API.

In Android Studio Project View, expand App > src > main > res > layout. Open the activity_main.xml layout file and click the Text tab to update the text contents of the file. Update it with the code below, which adds new Button and EditText controls for sending push notification messages to the notification hub. Add this code at the bottom, just before </RelativeLayout>.

 <Button
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:text="@string/send_button"
 android:id="@+id/sendbutton"
 android:layout_centerVertical="true"
 android:layout_centerHorizontal="true"
 android:onClick="sendNotificationButtonOnClick" />

 <EditText
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:id="@+id/editTextNotificationMessage"
 android:layout_above="@+id/sendbutton"
 android:layout_centerHorizontal="true"
 android:layout_marginBottom="42dp"
 android:hint="@string/notification_message_hint" />

In Android Studio Project View, expand App > src > main > res > values. Open the strings.xml file and add the string values that are referenced by the new Button and EditText controls. Add these at the bottom of the file, just before </resources>.
```
 <string name="send_button">Send Notification</string>
 <string name="notification_message_hint">Enter notification message text</string>
```
In your NotificationSetting.java file, add the following setting to the NotificationSettings class.

Update HubFullAccess with the DefaultFullSharedAccessSignature connection string for your hub. This connection string can be copied from the Azure Portal by clicking Access Policies on the Settings blade for your notification hub.
```
 public static String HubFullAccess = "<Enter Your DefaultFullSharedAccess Connection string>";
```

In your MainActivity.java file, add the following import statements above the MainActivity class.

 import java.io.BufferedOutputStream;
 import java.io.BufferedReader;
 import java.io.InputStreamReader;
 import java.io.OutputStream;
 import java.net.HttpURLConnection;
 import java.net.URL;
 import java.net.URLEncoder;
 import javax.crypto.Mac;
 import javax.crypto.spec.SecretKeySpec;
 import android.util.Base64;
 import android.view.View;
 import android.widget.EditText;

In your MainActivity.java file, add the following members at the top of the MainActivity class.

 private String HubEndpoint = null;
 private String HubSasKeyName = null;
 private String HubSasKeyValue = null;

You must create a Software Access Signature (SaS) token to authenticate a POST request to send messages to your notification hub. This is done by parsing the key data from the connection string and then creating the SaS token, as mentioned in the Common Concepts REST API reference. The following code is an example implementation.

In MainActivity.java, add the following method to the MainActivity class to parse your connection string.

 /**
  * Example code from http://msdn.microsoft.com/library/azure/dn495627.aspx
  * to parse the connection string so a SaS authentication token can be
  * constructed.
  *
  * @param connectionString This must be the DefaultFullSharedAccess connection
  *                         string for this example.
  */
 private void ParseConnectionString(String connectionString)
 {
     String[] parts = connectionString.split(";");
     if (parts.length != 3)
         throw new RuntimeException("Error parsing connection string: "
                 + connectionString);

     for (int i = 0; i < parts.length; i++) {
         if (parts[i].startsWith("Endpoint")) {
             this.HubEndpoint = "https" + parts[i].substring(11);
         } else if (parts[i].startsWith("SharedAccessKeyName")) {
             this.HubSasKeyName = parts[i].substring(20);
         } else if (parts[i].startsWith("SharedAccessKey")) {
             this.HubSasKeyValue = parts[i].substring(16);
         }
     }
 }

In MainActivity.java, add the following method to the MainActivity class to create a SaS authentication token.

 /**
  * Example code from http://msdn.microsoft.com/library/azure/dn495627.aspx to
  * construct a SaS token from the access key to authenticate a request.
  *
  * @param uri The unencoded resource URI string for this operation. The resource
  *            URI is the full URI of the Service Bus resource to which access is
  *            claimed. For example,
  *            "http://<namespace>.servicebus.windows.net/<hubName>"
  */
 private String generateSasToken(String uri) {

     String targetUri;
     String token = null;
     try {
         targetUri = URLEncoder
                 .encode(uri.toString().toLowerCase(), "UTF-8")
                 .toLowerCase();

         long expiresOnDate = System.currentTimeMillis();
         int expiresInMins = 60; // 1 hour
         expiresOnDate += expiresInMins * 60 * 1000;
         long expires = expiresOnDate / 1000;
         String toSign = targetUri + "\n" + expires;

         // Get an hmac_sha1 key from the raw key bytes
         byte[] keyBytes = HubSasKeyValue.getBytes("UTF-8");
         SecretKeySpec signingKey = new SecretKeySpec(keyBytes, "HmacSHA256");

         // Get an hmac_sha1 Mac instance and initialize with the signing key
         Mac mac = Mac.getInstance("HmacSHA256");
         mac.init(signingKey);

         // Compute the hmac on input data bytes
         byte[] rawHmac = mac.doFinal(toSign.getBytes("UTF-8"));

         // Using android.util.Base64 for Android Studio instead of
         // Apache commons codec
         String signature = URLEncoder.encode(
                 Base64.encodeToString(rawHmac, Base64.NO_WRAP).toString(), "UTF-8");

         // Construct authorization string
         token = "SharedAccessSignature sr=" + targetUri + "&sig="
                 + signature + "&se=" + expires + "&skn=" + HubSasKeyName;
     } catch (Exception e) {
         if (isVisible) {
             ToastNotify("Exception Generating SaS : " + e.getMessage().toString());
         }
     }

     return token;
 }

In MainActivity.java, add the following method to the MainActivity class to handle the Send Notification button click and send the push notification message to the hub by using the built-in REST API.

 /**
  * Send Notification button click handler. This method parses the
  * DefaultFullSharedAccess connection string and generates a SaS token. The
  * token is added to the Authorization header on the POST request to the
  * notification hub. The text in the editTextNotificationMessage control
  * is added as the JSON body for the request to add a GCM message to the hub.
  *
  * @param v
  */
 public void sendNotificationButtonOnClick(View v) {
     EditText notificationText = (EditText) findViewById(R.id.editTextNotificationMessage);
     final String json = "{\"data\":{\"message\":\"" + notificationText.getText().toString() + "\"}}";

     new Thread()
     {
         public void run()
         {
             try
             {
                 // Based on reference documentation...
                 // http://msdn.microsoft.com/library/azure/dn223273.aspx
                 ParseConnectionString(NotificationSettings.HubFullAccess);
                 URL url = new URL(HubEndpoint + NotificationSettings.HubName +
                         "/messages/?api-version=2015-01");

                 HttpURLConnection urlConnection = (HttpURLConnection)url.openConnection();

                 try {
                     // POST request
                     urlConnection.setDoOutput(true);

                     // Authenticate the POST request with the SaS token
                     urlConnection.setRequestProperty("Authorization", 
                         generateSasToken(url.toString()));

                     // Notification format should be GCM
                     urlConnection.setRequestProperty("ServiceBusNotification-Format", "gcm");

                     // Include any tags
                     // Example below targets 3 specific tags
                     // Refer to : https://azure.microsoft.com/en-us/documentation/articles/notification-hubs-routing-tag-expressions/
                     // urlConnection.setRequestProperty("ServiceBusNotification-Tags", 
                     //        "tag1 || tag2 || tag3");

                     // Send notification message
                     urlConnection.setFixedLengthStreamingMode(json.length());
                     OutputStream bodyStream = new BufferedOutputStream(urlConnection.getOutputStream());
                     bodyStream.write(json.getBytes());
                     bodyStream.close();

                     // Get reponse
                     urlConnection.connect();
                     int responseCode = urlConnection.getResponseCode();
                     if ((responseCode != 200) && (responseCode != 201)) {
                         BufferedReader br = new BufferedReader(new InputStreamReader((urlConnection.getErrorStream())));
                         String line;
                         StringBuilder builder = new StringBuilder("Send Notification returned " +
                                 responseCode + " : ")  ;
                         while ((line = br.readLine()) != null) {
                             builder.append(line);
                         }

                         ToastNotify(builder.toString());
                     }
                 } finally {
                     urlConnection.disconnect();
                 }
             }
             catch(Exception e)
             {
                 if (isVisible) {
                     ToastNotify("Exception Sending Notification : " + e.getMessage().toString());
                 }
             }
         }
     }.start();
 }

Testing your app

Push notifications in the emulator

If you want to test push notifications inside an emulator, make sure that your emulator image supports the Google API level that you chose for your app. If your image doesn't support native Google APIs, you will end up with the SERVICE_NOT_AVAILABLE exception.

In addition to the above, ensure that you have added your Google account to your running emulator under Settings > Accounts. Otherwise, your attempts to register with GCM may result in the AUTHENTICATION_FAILED exception.

Running the application

Run the app and notice that the registration ID is reported for a successful registration.
Enter a notification message to be sent to all Android devices that have registered with the hub.
Press Send Notification. Any devices that have the app running will show an AlertDialog instance with the push notification message. Devices that don't have the app running but were previously registered for push notifications will receive a notification in the Android Notification Manager. Those can be viewed by swiping down from the upper-left corner.

Next steps

We recommend the Use Notification Hubs to push notifications to users tutorial as the next step. It will show you how to send notifications from an ASP.NET backend using tags to target specific users.

If you want to segment your users by interest groups, check out the Use Notification Hubs to send breaking news tutorial.

To learn more general information about Notification Hubs, see our Notification Hubs Guidance.