Question

I’m asking for help so my life, and more importantly my user’s lives will not be ruined by me not knowing how to use Services and Threads correctly.

I’m not asking for a long explanation, but more of a confirmation. It’s fine if I’m dead wrong. I’m here to learn.

If I understand correctly:
1. a service runs in the background (no UI).
2. a service theoretically will run forever until it kills itself (I’m taking a big guess here)
3. a service will continue to run even when the main Activity is not visible (how about even destroyed?)

So here’s my coding question.

I’ve got my service setup and a thread. Everything works great, but it only works once. I need it to loop and keep checking back. Once it’s done run() how do I go about telling it to run() again?

public class NotifyService extends Service{

    private long mDoTask;

    NoteThread notethread;

    @Override
    public IBinder onBind(Intent arg0) {
        return null;
    }

    @Override
    public void onCreate() {
        mDoTask = System.currentTimeMillis();
        notethread = new NoteThread();
        notethread.start(); 
    }


    public class NoteThread extends Thread {
        NotificationManager nManager;
        Notification myNote;

        @Override
        public synchronized void start() {
            super.start();
//init some stuff
        }

        @Override
        public void run() {
                    //If it's been x time since the last task, do it again
            //For testing set to every 15 seconds...
            if(mDoTask + 15000 < System.currentTimeMillis()){

//Take care of business
        mDoTask = System.currentTimeMillis();                   
            }
        }
    }
}

Answer 1

From the Android docs:

A Service is an application component
representing either an application’s
desire to perform a longer-running
operation while not interacting with
the user or to supply functionality
for other applications to use. Each
service class must have a
corresponding declaration in
its package’s AndroidManifest.xml.
Services can be started with
Context.startService() and
Context.bindService().

Note that services, like other
application objects, run in the main
thread of their hosting process. This
means that, if your service is going
to do any CPU intensive (such as MP3
playback) or blocking (such as
networking) operations, it should
spawn its own thread in which to do
that work. More information on this
can be found in Processes and Threads.
The IntentService class is available
as a standard implementation of
Service that has its own thread where
it schedules its work to be done.

You can find a detailed discussion
about how to create services in the
Services document.

In other words, a service does NOT run in the background unless you put it in a thread. If you put a service that never ends in your application without manually threading the service, then it WILL block.

Android provides an API to do background tasks for you without having to poke around with Java threads; it’s called AsyncTask and it’s one of the few GOOD design decisions that the Android team has ever made.

EDIT I forgot to address your question about multithreading. You don’t want to make a thread execute its run() method more than once. Either instantiate a new thread or put a while loop around the contents of the run logic that you would like to have repeated.