TestActivity.java

public class TestActivity extends Activity {


    final Object uiHandlerLock = new Object();
    Button butt;
    HandlerThread thread;
    Handler backgroundHandler;
    Handler uiHandler;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        butt = new Button(this);
        butt.setText("Click me");
        butt.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                backgroundHandler.post(new Runnable() {

                    @Override
                    public void run() {
                        try {
                            Log.i("TAG", "the job started! Thread:" + Thread.currentThread().getId());
                            //do the job on background
                            Thread.sleep(1500);
                            synchronized (uiHandlerLock) {
                                if (uiHandler != null)
                                    //report back on Ui thread
                                    uiHandler.post(new Runnable() {
                                        @Override
                                        public void run() {
                                            Log.i("TAG", "the job done! Thread: " + Thread.currentThread().getId());
                                        }
                                    });
                            }

                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                });
            }
        });
        setContentView(butt);
    }

    @Override
    protected void onResume() {
        super.onResume();
        thread = new HandlerThread("test");
        thread.start();
        uiHandler = new Handler();
        backgroundHandler = new Handler(thread.getLooper());
        Log.i("TAG", "start UiThread:" + Thread.currentThread().getId());
    }

    @Override
    protected void onPause() {
        super.onPause();
        synchronized (uiHandlerLock) {
            uiHandler = null;
        }
        if (thread != null) {
            thread.quit();
            Log.i("TAG", "quit");
        }
        thread = null;
    }
}