Demo of using Handlers for async operations in Android

MainActivity.java

public class MainActivity extends AppCompatActivity {

  private static final int MSG_LONG_RUNNING_OPERATION = 101;
  private static final int MSG_UPDATE_UI = 102;
  private static final long THRITY_SECONDS = 30000;
  private Handler bgHandler;
  private Handler uiHandler;
  private Handler.Callback callback;
  private boolean doAgain = false;

  @Override protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    // Start our thread for background operations
    HandlerThread handlerThread = new HandlerThread("bg-thread");
    handlerThread.start();
    
    callback = new Handler.Callback() {
      @Override public boolean handleMessage(Message msg) {
        switch (msg.what) {
          case MSG_LONG_RUNNING_OPERATION:
            doLongRunningOperation();
            break;
          case MSG_UPDATE_UI:
            doUpdateUi((Bitmap) msg.obj);
            break;
        }
        return true;
      }
    };
    bgHandler = new Handler(handlerThread.getLooper(), callback);
    uiHandler = new Handler(Looper.getMainLooper(), callback);

    FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
    fab.setOnClickListener(new View.OnClickListener() {
      @Override public void onClick(View view) {
        bgHandler.sendEmptyMessage(MSG_LONG_RUNNING_OPERATION);
      }
    });
  }

  @Override protected void onDestroy() {
    super.onDestroy();
    doAgain = false;
    
    bgHandler.removeCallbacksAndMessages(null);
    uiHandler.removeCallbacksAndMessages(null);

    // Shut down the background thread
    bgHandler.getLooper().quit();
  }

  @WorkerThread private void doLongRunningOperation() {
    SystemClock.sleep(10000);

    Bitmap result = Bitmap.createBitmap(100, 100, Bitmap.Config.RGB_565);

    uiHandler.obtainMessage(MSG_UPDATE_UI, result).sendToTarget();

    if (doAgain) {
      bgHandler.sendEmptyMessageDelayed(MSG_LONG_RUNNING_OPERATION, THRITY_SECONDS);
    }
  }

  @MainThread private void doUpdateUi(Bitmap bitmap) {
    if (!doAgain) {
      // Do UI work
    }
  }

  @Override public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
  }

  @Override public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
      return true;
    }

    return super.onOptionsItemSelected(item);
  }
}