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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
- 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
- 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 @Override45 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)