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
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/
1 /*TestService.java */ 2 package com.android.server; 3 import android.content.Context; 4 import android.os.Handler; 5 import android.os.ITestService; 6 import android.os.Looper; 7 import android.os.Message; 8 import android.os.Process; 9 import android.util.Log; 10 public class TestService extends ITestService.Stub { 11 private static final String TAG = "TestService"; 12 private TestWorkerThread mWorker; 13 private TestWorkerHandler mHandler; 14 private Context mContext; 15 public TestService(Context context) { 16 super(); 17 mContext = context; 18 mWorker = new TestWorkerThread("TestServiceWorker"); 19 mWorker.start(); 20 Log.i(TAG, "Spawned worker thread"); 21 } 22 23 public void setValue(int val) { 24 Log.i(TAG, "setValue " + val); 25 Message msg = Message.obtain(); 26 msg.what = TestWorkerHandler.MESSAGE_SET; 27 msg.arg1 = val; 28 mHandler.sendMessage(msg); 29 } 30 31 private class TestWorkerThread extends Thread { 32 public TestWorkerThread(String name) { 33 super(name); 34 } 35 public void run() { 36 Looper.prepare(); 37 mHandler = new TestWorkerHandler(); 38 Looper.loop(); 39 } 40 } 41 42 private class TestWorkerHandler extends Handler { 43 private static final int MESSAGE_SET = 0; 44 @Override 45 public void handleMessage(Message msg) { 46 try { 47 if (msg.what == MESSAGE_SET) { 48 Log.i(TAG, "set message received: " + msg.arg1); 49 } 50 } catch (Exception e) { 51 // Log, don‘t crash! 52 Log.e(TAG, "Exception in TestWorkerHandler.handleMessage:", e); 53 } 54 } 55 } 56 }
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
(from:http://processors.wiki.ti.com/index.php/Android-Adding_SystemService)