Activity or Service?

I'm building a Bluetooth application. I want to periodically scan for nearby Bluetooth devices. This program should start when the device starts and continue discovering devices based on a schedule (every 10 mins for example). I've been looking over the Android ex开发者_开发百科ample of "BlueTooth Chat" in the API documentation, and I don't kow why it never uses the "Service" class. Should I use Service or Activity?

Furthermore, I understand that Services are supposed to be used for "long running tasks," but I also at some point want to provide some kind of GUI notification to the users via this class that discovers Bluetooth devices.

So, can someone please explain which one to use? What is the advantage?

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You should use service if you want your scheduling running.Because android will eventually destroy your activity.

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Definitely use a Service. In your MainActivity bind to the Service using bindService providing a ServiceConnection object. In this ServiceConnection object send a Message to the service with a reference to a local Messenger object (as part of a replyTo) that the Service can then use to later on send a Message back to your MainActivity. This will enable you to update your MainActivity GUI based on the results of your bluetooth scan.

In short, in your MainActivity, start and bind to your service with:

Intent i = new Intent(this, NetworkService.class);
startService(i);
bindService(i, networkServiceConnection, Context.BIND_AUTO_CREATE);

Define a messenger to respond to messages from the service like:

Messenger messenger = new Messenger(new IncomingHandler());

class IncomingHandler extends Handler {
    @Override
    public void handleMessage(Message msg) {
        switch (msg.what) {
            case NetworkService.MSG_SOMETHING:
                // do something here
                break;
            default:
                super.handleMessage(msg);
        }
    }
}

And then write your service connection code like:

private ServiceConnection networkServiceConnection = new ServiceConnection() {
    public void onServiceConnected(ComponentName className, IBinder service) {
        networkService = new Messenger(service);
        try {
            Message msg = Message.obtain(null, NetworkService.MSG_REGISTER_CLIENT);
            msg.replyTo = messenger;
            networkService.send(msg);
            log.debug("Connected to service");

        } catch (RemoteException e) {
            // Here, the service has crashed even before we were able to connect
        }
    }

Note that the replyTo is the messenger we just created.

In your NetworkService, keep track of connected clients with:

ArrayList<Messenger> clients = new ArrayList<Messenger>();

and create your handler like:

class IncomingHandler extends Handler {
       @Override
       public void handleMessage(Message msg) {
           switch (msg.what) {
               case MSG_REGISTER_CLIENT:
                   log.debug("Adding client: " + msg.replyTo);
                   clients.add(msg.replyTo);
                   break;
               default:
                   super.handleMessage(msg);
                   break;
           }
       }
   }

Then, when you want to send a message back to your MainActivity, just do something like the following:

for (int i = 0; i < clients.size(); i++) {
    try {
        clients.get(i).send(Message.obtain(null, MSG_SOMETHING));
    } catch (RemoteException e) {
        // If we get here, the client is dead, and we should remove it from the list
        log.debug("Removing client: " + clients.get(i));
        clients.remove(i);
    }
}