GCM Demo Application

Note: This tutorial describes how to develop GCM-enabled apps using the helper libraries. This is just one approach. For a more comprehensive discussion of the available APIs and development paths, see Getting Started.

The Google Cloud Messaging (GCM) Demo demonstrates how to use the Google Cloud Messaging framework in your Android application. This tutorial walks you through setting up and running the demo.

This demo consists of the following pieces:

• A web server containing a page where you can send messages.
• An Android application that receives and displays such messages.

See the reference for the client and server helper libraries used in this demo.

The sections below describe how to download the demo code and helper libraries from the SDK Manager. The demo code and helper libraries are also available at the open source site.

Requirements

For the web server:

• Ant 1.8 (it might work with earlier versions, but it's not guaranteed).
• One of the following:
  • A running web server compatible with Servlets API version 2.5, such as Tomcat 6 or Jetty, or
  • Java App Engine SDK version 1.6 or later.
• A Google account registered to use GCM.
• The API key for that account.

For the Android application:

• Emulator (or device) running Android 2.2 with Google APIs.
• The Google API project number of the account registered to use GCM.

Setting Up GCM

Before proceeding with the server and client setup, it's necessary to register a Google account with the Google API Console, enable Google Cloud Messaging in GCM, and obtain an API key from the Google API Console.

For instructions on how to set up GCM, see Getting Started.

Setting Up the Server

This section describes the different options for setting up a server.

Using a standard web server

To set up the server using a standard, servlet-compliant web server:

1. From the SDK Manager, install Extras > Google Cloud Messaging for Android Library.

   This creates a gcm directory under YOUR_SDK_ROOT/extras/google/ containing these subdirectories: 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.

2. In a text editor, edit the samples/gcm-demo-server/WebContent/WEB-INF/classes/api.key and replace the existing text with the API key obtained above.
3. In a shell window, go to the samples/gcm-demo-server directory.
4. Generate the server's WAR file by running ant war:

$ ant war

Buildfile:build.xml

init:
   [mkdir] Created dir: build/classes
   [mkdir] Created dir: dist

compile:
   [javac] Compiling 6 source files to build/classes

war:
     [war] Building war: dist/gcm-demo.war

BUILD SUCCESSFUL
Total time: 0 seconds

5. Deploy the dist/gcm-demo.war to your running server. For instance, if you're using Jetty, copy gcm-demo.war to the webapps directory of the Jetty installation.
6. Open the server's main page in a browser. The URL depends on the server you're using and your machine's IP address, but it will be something like http://192.168.1.10:8080/gcm-demo/home, where gcm-demo is the application context and /home is the path of the main servlet.

Note: You can get the IP by running ifconfig on Linux or MacOS, or ipconfig on Windows.

You server is now ready.

Using App Engine for Java

To set up the server using a standard App Engine for Java:

1. From the SDK Manager, install Extras > Google Cloud Messaging for Android Library.

   This creates a gcm directory under YOUR_SDK_ROOT/extras/google/ containing these subdirectories: gcm-client, gcm-server, samples/gcm-demo-client, samples/gcm-demo-server, and samples/gcm-demo-appengine.

2. In a text editor, edit samples/gcm-demo-appengine/src/com/google/android/gcm/demo/server/ApiKeyInitializer.java and replace the existing text with the API key obtained above.

   Note: The API key value set in that class will be used just once to create a persistent entity on App Engine. If you deploy the application, you can use App Engine's Datastore Viewer to change it later.

3. In a shell window, go to the samples/gcm-demo-appengine directory.
4. Start the development App Engine server by ant runserver, using the -Dsdk.dir to indicate the location of the App Engine SDK and -Dserver.host to set your server's hostname or IP address:

$ ant -Dsdk.dir=/opt/google/appengine-java-sdk runserver -Dserver.host=192.168.1.10
Buildfile: gcm-demo-appengine/build.xml

init:
    [mkdir] Created dir: gcm-demo-appengine/dist

copyjars:

compile:

datanucleusenhance:
  [enhance] DataNucleus Enhancer (version 1.1.4) : Enhancement of classes
  [enhance] DataNucleus Enhancer completed with success for 0 classes. Timings : input=28 ms, enhance=0 ms, total=28 ms. Consult the log for full details
  [enhance] DataNucleus Enhancer completed and no classes were enhanced. Consult the log for full details

runserver:
     [java] Jun 15, 2012 8:46:06 PM com.google.apphosting.utils.jetty.JettyLogger info
     [java] INFO: Logging to JettyLogger(null) via com.google.apphosting.utils.jetty.JettyLogger
     [java] Jun 15, 2012 8:46:06 PM com.google.apphosting.utils.config.AppEngineWebXmlReader readAppEngineWebXml
     [java] INFO: Successfully processed gcm-demo-appengine/WebContent/WEB-INF/appengine-web.xml
     [java] Jun 15, 2012 8:46:06 PM com.google.apphosting.utils.config.AbstractConfigXmlReader readConfigXml
     [java] INFO: Successfully processed gcm-demo-appengine/WebContent/WEB-INF/web.xml
     [java] Jun 15, 2012 8:46:09 PM com.google.android.gcm.demo.server.ApiKeyInitializer contextInitialized
     [java] SEVERE: Created fake key. Please go to App Engine admin console, change its value to your API Key (the entity type is 'Settings' and its field to be changed is 'ApiKey'), then restart the server!
     [java] Jun 15, 2012 8:46:09 PM com.google.appengine.tools.development.DevAppServerImpl start
     [java] INFO: The server is running at http://192.168.1.10:8080/
     [java] Jun 15, 2012 8:46:09 PM com.google.appengine.tools.development.DevAppServerImpl start
     [java] INFO: The admin console is running at http://192.168.1.10:8080/_ah/admin

5. Open the server's main page in a browser. The URL depends on the server you're using and your machine's IP address, but it will be something like http://192.168.1.10:8080/home, where /home is the path of the main servlet.

Note: You can get the IP by running ifconfig on Linux or MacOS, or ipconfig on Windows.

You server is now ready.

Setting Up the Device

To set up the device:

1. From the SDK Manager, install Extras > Google Cloud Messaging for Android Library.

   This creates a gcm directory under YOUR_SDK_ROOT/extras/google containing these subdirectories: gcm-client, gcm-server, samples/gcm-demo-client, samples/gcm-demo-server, and samples/gcm-demo-appengine.

2. Using a text editor, open samples/gcm-demo-client/src/com/google/android/gcm/demo/app/CommonUtilities.java and set the proper values for the SENDER_ID and SERVER_URL constants. For example:

static final String SERVER_URL = "http://192.168.1.10:8080/gcm-demo";
static final String SENDER_ID = "4815162342";

Note that the SERVER_URL is the URL for the server and the application's context (or just server, if you are using App Engine), and it does not include the forward slash (/). Also note that SENDER_ID is the Google API project number you obtained in the server setup steps above.

3. In a shell window, go to the gcm-demo-client directory.
4. Use the SDK's android tool to generate the ant build files:

$ android update project --name GCMDemo -p . --target android-16
Updated project.properties
Updated local.properties
Updated file ./build.xml
Updated file ./proguard-project.txt

If this command fails becase android-16 is not recognized, try a different target (as long as it is at least android-15).

5. Use ant to build the application's APK file:

$ ant clean debug
Buildfile: build.xml

...


-do-debug:
[zipalign] Running zip align on final apk...
    [echo] Debug Package: bin/GCMDemo-debug.apk
[propertyfile] Creating new property file: bin/build.prop
[propertyfile] Updating property file: bin/build.prop
[propertyfile] Updating property file: bin/build.prop
[propertyfile] Updating property file: bin/build.prop

-post-build:

debug:

BUILD SUCCESSFUL
Total time: 3 seconds
 

6. Start the Android emulator:

$emulator -avd my_avd

This example assumes there is an AVD (Android Virtual Device) named my_avd previously configured with Android 2.2 and Google APIs level 8. For more information on how to run an Android emulator, see Managing Virtual Devices in the Android Developers Guide.

7. Make sure there is a Google account added to the emulator. It doesn't have to be any account (like the senderId) in particular.

If the emulator is running Android 4.0.4 or later, this step is optional as GCM does not require an account from this version on.

8. Install the application in the emulator:

$ ant installd
Buildfile: gcm-demo-client/build.xml

-set-mode-check:

-set-debug-files:

install:
     [echo] Installing gcm-demo-client/bin/GCMDemo-debug.apk onto default emulator or device...
     [exec] 1719 KB/s (47158 bytes in 0.026s)
     [exec]   pkg: /data/local/tmp/GCMDemo-debug.apk
     [exec] Success

installd:

BUILD SUCCESSFUL
Total time: 3 seconds

9. In the emulator, launch the GCM Demo app. The initial screen should look like this:



Note: What happened? When the device received a registration callback intent from GCM, it contacted the server to register itself, using the register servlet and passing the registration ID received from GCM; the server then saved the registration ID to use it to send messages to the phone.

10. Now go back to your browser and refresh the page. It will show that there is one device registered:



11. Click on Send Message. The browser should show:



And in your emulator:



Note: What happened? When you clicked the button, the web server sent a message to GCM addressed to your device (more specifically, to the registration ID returned by GCM during the registration step). The device then received the message and displayed in the main activity; it also issued a system notification so the user would be notified even if the demo application was not running.