Tutorial: Push notifications to Android devices by using Azure Notification Hubs and Google Cloud Messaging (deprecated)

Warning

As of April 10, 2018, Google has deprecated Google Cloud Messaging (GCM). The GCM server and client APIs are deprecated and will be removed as soon as May 29, 2019. For more information, see GCM and FCM Frequently Asked Questions.

Overview

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

Important

The Google Cloud Messaging (GCM) is deprecated and will be removed soon.

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.

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

In this tutorial, you do the following actions:

  • Create a project that supports Google Cloud Messaging.
  • Create a notification hub
  • Connect your app to the notification hub
  • Test the app

Prerequisites

Creating a project that supports Google Cloud Messaging

  1. Navigate to the Google Cloud Console, sign in with your Google account credentials.

  2. Select Create Project on the toolbar.

    Create new project

  3. For Project name, enter a name for your project, and click Create.

  4. Select the alerts button on the toolbar, and select your project in the list. You see the dashboard for your project. You can also navigate directly to the dashboard by using the URL: https://console.developers.google.com/home/dashboard?project=<YOUR PROJECT NAME>

    Select your project in alerts

  5. Note down the Project number in the Project info tile of the dashboard.

    Project ID

  6. In the dashboard, on the APIs tile, select Got to APIs overview.

    API overview link

  7. On the API page, select ENABLE APIS AND SERVICES.

    Enable APIs and Services button

  8. Search for and select Google Cloud Messaging.

    Search for and select Google Cloud Messaging

  9. To enable Google Cloud Messaging for the project, select ENABLE.

    Enable Google Cloud Messaging

  10. Select Create credentials on the toolbar.

    Create credentials button

  11. On the Add credentials to your project page, select API key link.

    Create credentials button

  12. On API key page, select Create/Save. In the following example, the IP addresses option is selected, and 0.0.0.0/0 is entered for allowed IP addresses. You should restrict your API key appropriately.

    API Key - Create button

  13. Copy the API key to the clipboard, and save it somewhere.

    Copy API key

    You will use this API key value to enable Azure to authenticate with GCM and send push notifications on behalf of your app. To navigate back to the project dashboard, use the URL: https://console.developers.google.com/home/dashboard?project=<YOUR PROJECT NAME>

Create a notification hub

  1. Sign in to the Azure portal.

  2. Select All services on the left menu, and then select Notification Hubs in the Mobile section. Select the star icon next to the service name to add the service to the FAVORITES section on the left menu. After you add Notification Hubs to FAVORITES, select it on the left menu.

    Azure portal - select Notification Hubs

  3. On the Notification Hubs page, select Add on the toolbar.

    Notification Hubs - Add toolbar button

  4. On the Notification Hub page, do the following steps:

    1. Enter a name in Notification Hub.

    2. Enter a name in Create a new namespace. A namespace contains one or more hubs.

    3. Select a value from the Location drop-down list box. This value specifies the location in which you want to create the hub.

    4. Select an existing resource group in Resource Group, or create a name for a new resource group.

    5. Select Create.

      Azure portal - set notification hub properties

  5. Select Notifications (the bell icon), and then select Go to resource. You can also refresh the list on the Notification Hubs page and select your hub.

    Azure portal - notifications -> Go to resource

  6. Select Access Policies from the list. Note that the two connection strings are available to you. You'll need them later to handle push notifications.

    Important

    Do not use the DefaultFullSharedAccessSignature policy in your application. This is meant to be used in your back end only.

    Azure portal - notification hub connection strings

Configure GCM setting for the notification hub

  1. Select Google (GCM) in NOTIFICATION SETTINGS.

  2. Enter API Key you got from the Google Cloud Console.

  3. Select Save on the toolbar.

    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

  1. In Android Studio, start a new Android Studio project.

    Android Studio - new project

  2. Choose the Phone and Tablet form factor and the Minimum SDK that you want to support. Then click Next.

    Android Studio - project creation workflow

  3. Choose Empty Activity for the main activity, click Next, and then click Finish.

Add Google Play services to the project

  1. In Android Studio, select Tools on the menu, and then select SDK Manager.

  2. Select the target version of the Android SDK that is used in your project. Then select Show Package Details.

    Android SDK Manager - select target version

  3. Select Google APIs, if it's not already installed.

    Android SDK Manager - Google APIs selected

  4. Switch to the SDK Tools tab. If you haven't already installed Google Play Services, select Google Play Services as shown in the following image. Then select Apply to install. Note the SDK path, for use in a later step.

    Android SDK Manager - Google Play Services selected

  5. If you see the Confirm Change dialog box, select OK. The Component Installer installs the requested components. Select Finish after the components are installed.

  6. Select OK to close the Settings for New Projects dialog box.

  7. Open the build.gradle file in the app directory, and then add the following line under dependencies.

    implementation 'com.google.android.gms:play-services-gcm:16.0.0'
    
  8. Select Sync Now icon in the toolbar.

    Sync with Gradle

  9. Open the AndroidManifest.xml file, and then add the following 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

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

    implementation 'com.microsoft.azure:notification-hubs-android-sdk:0.6@aar'
    implementation 'com.microsoft.azure:azure-notifications-handler:1.0.1@aar'
    
  2. Add the following repository after the dependencies section.

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

Updating the project's AndroidManifest.xml

  1. To support GCM, implement an Instance ID listener service in the code that is used to obtain registration tokens using Google's Instance ID API. In this tutorial, the name of the class is MyInstanceIDService.

    Add the following service definition to the AndroidManifest.xml file, inside the <application> tag. Replace the <your package> placeholder with 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>
    
  2. Once the application receives the GCM registration token from the Instance ID API, it uses the token to register with the Azure Notification Hub. The registration in the background is done using an IntentService named RegistrationIntentService. This service is responsible for refreshing the GCM registration token.

    Add the following service definition to the AndroidManifest.xml file, inside the <application> tag. Replace the <your package> placeholder with your actual package name shown at the top of the AndroidManifest.xml file.

    <service
        android:name="<your package>.RegistrationIntentService"
        android:exported="false">
    </service>
    
  3. 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 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>
    
  4. Add the following necessary GCM permissions below the </application> tag. 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

  1. 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.

    Android Studio - new Java class

    Update the 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 page of your hub on the Azure portal.

    • HubName: Use the name of your notification hub that appears in the hub page 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>";
      }
      
  2. Add another new class named MyInstanceIDService. This class is the Instance ID listener service implementation.

    The code for this class calls 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);
        }
    };
    
  3. Add another new class to your project named, RegistrationIntentService. This class implements IntentService that handles 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/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 the 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);
            }
        }
    }
    
  4. In your MainActivity class, add the following import statements at the beginning of the class.

    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;
    import android.content.Intent;
    
  5. Add the following private members at the top of the class. This code checks 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;
    private static final String TAG = "MainActivity";
    
  6. 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;
    }
    
  7. In your MainActivity class, add the following code that checks 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);
        }
    }
    
  8. 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();
    }
    
  9. 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);
            }
        });
    }
    
  10. 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"
    
  11. Add a subclass for the receiver that's defined in the AndroidManifest.xml. Add another new class to your project named MyHandler.

  12. 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;
    import android.net.Uri;
    import android.media.RingtoneManager;
    
  13. 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 reports 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());
        }
    }
    
  14. In Android Studio on the menu bar, click Build > Rebuild Project to make sure that no errors are present in your code.

Testing your app

Run the mobile application

  1. Run the app and notice that the registration ID is reported for a successful registration.

    Testing on Android - Channel registration

  2. Enter a notification message to be sent to all Android devices that have registered with the hub.

    Testing on Android - sending a message

  3. Press Send Notification. Any devices that have the app running shows an AlertDialog instance with the push notification message. Devices that don't have the app running but were previously registered for push notifications receive a notification in the Android Notification Manager. The notification messages can be viewed by swiping down from the upper-left corner.

    Testing on Android - notifications

Test send push notifications from the Azure portal

You can test receiving push notifications in your app by sending them via the Azure portal.

  1. In the Troubleshooting section, select Test Send.

  2. For Platforms, select Android.

  3. Select Send to send the test notification.

  4. Confirm that you see the notification message on the Android device.

    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. If a library isn't available for your back end, you can also use the REST API directly to send notification messages.

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

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 end up with the SERVICE_NOT_AVAILABLE exception.

In addition, 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.

(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.

  1. 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" />
    
  2. 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 the following lines 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>
    
  3. 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 page for your notification hub.

    public static String HubFullAccess = "<Enter Your DefaultFullSharedAccess Connection string>";
    
  4. In your MainActivity.java file, add the following import statements at the beginning of the file.

    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;
    
  5. 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;
    
  6. Create a Software Access Signature (SaS) token to authenticate a POST request to send messages to your notification hub. Parse 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 https://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);
            }
        }
    }
    
  7. In MainActivity.java, add the following method to the MainActivity class to create a SaS authentication token.

    /**
        * Example code from https://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;
    }
    
  8. 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...
                    // https://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/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 response
                        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();
    }
    

Next steps

In this tutorial, you sent broadcast notifications to all your Android devices registered with the backend. To learn how to push notifications to specific Android devices, advance to the following tutorial: