Google provides a service named Google Cloud Message (GCM) which allows developers to send data to their applications running on Android devices. Unlike most solutions which involve polling some server, this service is a "push" service (similar to SMS messages).
GCM replaces the previous service named C2DM. This framework is a modified version of the previous C2DM framework that works with the new service.
Note that new GCM service is simpler than C2DM and doesn't require a special approval from Google.
Developers should implement three components in order to use this service.
Client code -
The client code which is responsible for registering the specific device and application with Google service and is responsible for handling new messages that arrive.
Web server -
When the device registers with Google service it receives a registration id that allows you, the account holder, to send messages to your application running on the user device. The device needs to send this id to a web server that you can access.
Messages sending tool -
This is a command line tool that is responsible for fetching the user id from the web server and then sending the message to the device. This is done by sending a request to Google servers.
The attached framework includes these components.
It is recommended to read the formal documentation about GCM to better understand the flow: GCM Architectural Overview | Android Developers
Configuration and installation instructions
In order to use GCM service you need to get two values: API key and project id.
This is done by following the steps mentioned here: GCM: Getting Started | Android Developers
up until the "Install the Helper Libraries" section (there is no need to install anything).
In order to get it working, we will modify the device example application. Later you can integrate this code in your own application.
1. SenderId variable should be set in the Main activity, under Sub Process_Globals to match project ID you previously received.
2. You should add the following code to the manifest editor (this is already set in the attached example):
Sending messages desktop tool
AddManifestText(<permission android:name="$PACKAGE$.permission.C2D_MESSAGE" android:protectionLevel="signature" />)
' Push Service Receiver Attribute
SetReceiverAttribute(PushService, android:permission, "com.google.android.c2dm.permission.SEND")
' Service Receiver Text
<action android:name="com.google.android.c2dm.intent.RECEIVE" />
<category android:name="$PACKAGE$" />
<action android:name="com.google.android.c2dm.intent.REGISTRATION" />
<category android:name="$PACKAGE$" />
1. Open config.txt and update the api_key field.
You are now ready to test it!
Run the B4A project, enter a name in the text field and press on the Register button. You should see a toast message saying Registration successful. Messages are also printed to the logs. It can take several seconds.
This means two things. Your device has registered with Google servers and also that the registration id was sent to the developer web service (currently configured with the service hosted here) with the specified name.
The name will be used to reference the device. Note that each device must have a unique name.
Now go to the command line tool folder and open a command window (this can be done by pressing Shift together with right clicking on the folder icon).
The sending messages tool is a java app. For your convenience a batch file is included to run this tool. Note that this app can run from Linux or Mac as well.
The sending tool expects several arguments:
send <device name> <message text> [<collapse_key> [<delay while sleeping>]]
Device name is the name that you previously chose in the client app.
Message text is the text that will be sent. Remember to wrap it with quotes if it contains spaces.
The last two arguments are optional. See the formal documentation for more information about them.
Instead of 'send' command, you can use 'SendTextFile'. It is the same as send, however the second argument is the path to a text file that will be sent.
Another command is 'GetAll'. It will display all the registered device names (this command is not available in the web service hosted here.
The command line tool can be automated. It returns an exit code of 0 if the operation succeeded and 1 otherwise.
Try sending a message to your device. It should arrive to the device almost immediately.
Note that the batch file name is b4a_gcm.bat.
Handling of messages is done in Sub MessageArrived in PushService module.
Web server configuration
The device application and the sending messages tool are preconfigured to use the web server hosted here. This server should only be used during development.
The web server is built from a PHP script which communicates with a MySQL database.
In order to host it yourself, you should upload it to a server that supports PHP and create a database and user that is able to access the database.
The script creates the table on the first run.
You will need to edit the PHP script and set the database name / user / password.
There are additional two passwords in this script: devicepassword and serverpassword. The device password should match the DeviceBoardPassword field in the device application and the serverpassword should match the server_password field in the sending messages tool configuration. Both these passwords should only contain letters and numbers.
You should also change the board url value in the desktop tool and device app to match the location of your hosted php file.