【Quote】 Android-Adding SystemService

From http://processors.wiki.ti.com/index.php/Android-Adding_SystemService

 

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.

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

• 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

Support

For community support join http://groups.google.com/group/rowboat 
For IRC #rowboat on irc.freenode.net