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;@Overridepublic 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