Android-Adding SystemService

This wiki page will demonstrate - "How to add system service to android framework". Example - "Adding a Bluetooth HID service" - taken as reference of understanding.This will also help to add
support for more bluetooth profiles into android framework.

Contents [hide] 1 What is service? 2 Service layer 3 Create service 4 Register service 5 Expose service 6 Add [service].aidl for build 7 Using service 8 References 9 Support

What is service?

As per the definition given at http://developer.android.com/guide/topics/fundamentals/services.html
A Service is an application component that can perform long-running operations in the background and does not provide a user interface. Another application component can start
a service and it will continue to run in the background even if the user switches to another application. Additionally, a component can bind to a service to interact with it and even perform interprocess communication (IPC). For example, a service might handle
network transactions, play music, perform file I/O, or interact with a content provider, all from the background.

Service layer

Create service

1. Add your code to frameworks/base/services/java/com/android/server/

/*TestService.java */
package com.android.server;
import android.content.Context;
import android.os.Handler;
import android.os.ITestService;
import android.os.Looper;
import android.os.Message;
import android.os.Process;
import android.util.Log;
public class TestService extends ITestService.Stub {
private static final String TAG = "TestService";
private TestWorkerThread mWorker;
private TestWorkerHandler mHandler;
private Context mContext;
public TestService(Context context) {
super();
mContext = context;
mWorker = new TestWorkerThread("TestServiceWorker");
mWorker.start();
Log.i(TAG, "Spawned worker thread");
}

public void setValue(int val) {
Log.i(TAG, "setValue " + val);
Message msg = Message.obtain();
msg.what = TestWorkerHandler.MESSAGE_SET;
msg.arg1 = val;
mHandler.sendMessage(msg);
}

private class TestWorkerThread extends Thread{
public TestWorkerThread(String name) {
super(name);
}
public void run() {
Looper.prepare();
mHandler = new TestWorkerHandler();
Looper.loop();
}
}

private class TestWorkerHandler extends Handler {
private static final int MESSAGE_SET = 0;
@Override
public void handleMessage(Message msg) {
try {
if (msg.what == MESSAGE_SET) {
Log.i(TAG, "set message received: " + msg.arg1);
}
}catch (Exception e) {
// Log, don't crash!
Log.e(TAG, "Exception in TestWorkerHandler.handleMessage:", e);
}
}
}
}

Register service

Register service in SystemServer.java

/*
* go to function "@Override public void run()"
* ........
* Add following block after line "if (factoryTest != SystemServer.FACTORY_TEST_LOW_LEVEL) {"
*/

try {
Slog.i(TAG, "Test Service");
ServiceManager.addService(“Test”, new TestService(context));
} catch (Throwable e) {
Slog.e(TAG, "Failure starting TestService Service", e);
}

Expose service

A service can expose set of functions that can be access by other process/application. Exposed functions are required to be declared in .aidl file at following location

frameworks/base/core/java/android/os/[server].aidl

/*
* aidl file : frameworks/base/core/java/android/os/ITestService.aidl
* This file contains definitions of functions which are exposed by service
*/
package android.os;
interface ITestService {
/**
* {@hide}
*/
void setValue(int val);
}

Add [service].aidl for build

/*
* open frameworks/base/Android.mk and add following line
*/
...
core/java/android/os/IPowerManager.aidl \
core/java/android/os/ITestService.aidl \
core/java/android/os/IRemoteCallback.aidl \
...

Rebuild the framework/base or android system.Service is now ready to use by other application/process.

Using service

To use service

first get service handle using "ServiceManager.getService()" api
use service handle to call set of functions exposed by service

Below is the sample code to use service.

/*
* HelloServer.java
*/
package com.Test.helloserver;
import android.app.Activity;
import android.os.Bundle;
import android.os.ServiceManager;
import android.os.ITestService;
import android.util.Log;
public class HelloServer extends Activity {
private static final String DTAG = "HelloServer";
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

ITestService om = ITestService.Stub.asInterface(ServiceManager.getService("Test"));
try {
Log.d(DTAG, "Going to call service");
om.setValue(20);
Log.d(DTAG, "Service called succesfully");
}
catch (Exception e) {
Log.d(DTAG, "FAILED to call service");
e.printStackTrace();
}
}
}

References

http://developer.android.com/reference/android/app/Service.html
http://developer.android.com/guide/topics/fundamentals/services.html
http://www.opersys.com/blog/esc-india-2011-wrapup