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/

 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)