Question

I have to call, from a Service android, a method for opening connection with internal android database (sqlite). I’m using the following code:

public class myService extends Service{

public void setDB(DB_DatabaseManager db){
    dbManager = db;
}

public DB_DatabaseManager dbManager;
private Timer timer; 

public IBinder onBind(Intent intent){
    return null;
}

public void onCreate(){
    super.onCreate();
    Log.i("my attempt","service activated");
    TimerTask task = new TimerTask(){
        public void run(){
            Log.i("my attempt","ANDROID SERVICE RUNNING!");
            dbManager.open(); // <--this statement generates error!
                            // --- in this section I start the communication with database

        }

    };
    timer = new Timer();
    timer.schedule(task, 0, 20000);
}

public void onDestroy(){
    super.onDestroy();
    timer.cancel();
    timer = null;
    Log.i("my attampt", "service stopped");
}

open() is defined as:

    SQLiteDatabase mDb=mDbHelper.getWritableDatabase();

For calling the service I use:

    myService serv = new myService();
    serv.setDB(dbManager); 
    startService(new Intent(this,myService.class));

all work fine if I delete the row dbManager.open();
however the method dbManager.open() in other parts of my coode, works good. But in this situation i obtain the following error in logcat:

   09-14 23:44:32.287: E/AndroidRuntime(1115): FATAL EXCEPTION: Timer-0
   09-14 23:44:32.287: E/AndroidRuntime(1115): java.lang.NullPointerException
   09-14 23:44:32.287: E/AndroidRuntime(1115):  at host.framework.myService$1.run(myService.java:49)
   09-14 23:44:32.287: E/AndroidRuntime(1115):  at java.util.Timer$TimerImpl.run(Timer.java:284)

Answer 1

Do not try to do this…

myService serv = new myService();

Similar to the Activity class, Service is a “special case” class and you should never try to create an instance using new.

A Service is created using either bindService(...) or startService(...) and it is the responsibility of the OS to create/instantiate it.

In your case it seems you need your Service to be able to access a database “helper” class and there are a number of ways you could do this.

One way is to extend the Application class and have it create an instance of the db helper and hold a static reference to it. In this way in the Service, you can simply use…

MyApp.mDbHelper.open();

Alternatively use the singleton model for your db helper which would allow you to do something like the following in the Service…

DB_DatabaseManager.getInstance().open();