Dismiss Ongoing Android Notification Via Action Button Without Opening App

The accepted solution is not working in Android 8.1 and onwards.

Follow the same steps as in the accepted answer, but update this line:

//Create the PendingIntent
PendingIntent btPendingIntent = PendingIntent.getBroadcast(context, 0, buttonIntent, PendingIntent.FLAG_UPDATE_CURRENT);

See also PendingIntent.FLAG_UPDATE_CURRENT

Start with this:

int final NOTIFICATION_ID = 1;

//Create an Intent for the BroadcastReceiver
Intent buttonIntent = new Intent(context, ButtonReceiver.class);
buttonIntent.putExtra("notificationId",NOTIFICATION_ID);

//Create the PendingIntent
PendingIntent btPendingIntent = PendingIntent.getBroadcast(context, 0, buttonIntent,0);

//Pass this PendingIntent to addAction method of Intent Builder
NotificationCompat.Builder mb = new NotificationCompat.Builder(getBaseContext());
.....
.....
.....
mb.addAction(R.drawable.ic_Action, "My Action", btPendingIntent);
manager.notify(NOTIFICATION_ID, mb.build());  

Create the BroadcastReceiver:

public class ButtonReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {

        int notificationId = intent.getIntExtra("notificationId", 0);

        // Do what you want were.
        ..............
        ..............

        // if you want cancel notification
        NotificationManager manager = (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);
        manager.cancel(notificationId);
    }
}  

If you don´t want show any activity when user click on notification, define the intent passed in setContentIntent in this way:

PendingIntent resultPendingIntent = PendingIntent.getActivity(context,  0, new Intent(), 0);
......
......
mb.setContentIntent(resultPendingIntent); 

To close notification tray when clicked, call setAutoCancel() with true when building the notification: mb.setAutoCancel(true);