Can a Broadcast Receiver send information to an Activity only if it is active without starting a new Activity?

Question

I have a broadcast receiver that gets triggered on geofencing events and either "clocks in" or "clocks out" with the server. If my application's "Attendance" activity is already open I would like it to display the clocking status change but I don't want the Broadcast Receiver to start the activity if it's not open - in other words display the change "live" while the activity is open only.

The way I imagine doing this is with the Broadcast Receiver sending an Intent to the activity but name "startActivity()" doesn't sound encouraging unless there are any special flags I can pass to prevent starting an Activity that isn't already open - I can't seem to find any.

The other option would be to constantly poll the value while the activity is open but it doesn't seem optimal so I would only use it if there wasn't another way and I can't think of a reason why it couldn't be possible with Intents.

Answer 1

There are several different ways to accomplish the same task. One is registering a listener like the following example:

MainActivity

public class MainActivity extends AppCompatActivity
{
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    
        Receiver.setOnReceiveListener(new Receiver.OnReceiveListener() {
            public void onReceive(Context Context, Intent intent)
            {
                //Do something.
            }
        });
    }

    @Override
    protected void onDestroy()
    {
        super.onDestroy();
        Receiver.setOnReceiveListener(null);
    }
}

Receiver

public class Receiver extends BroadcastReceiver
{
    private static OnReceiveListener static_listener;

    public static abstract interface OnReceiveListener
    {
        public void onReceive(Context context, Intent intent);
    }

    public static void setOnReceiveListener(OnReceiveListener listener)
    {
        static_listener = listener;
    }


    @Override
    public final void onReceive(Context context, Intent intent)
    {
        if(static_listener != null) {
            static_listener.onReceive(context, intent);
        }
    }
}