How to send data from Arduino-uno using Bluetooth module HC-05 and read it in Android?

Question

I am able to send data from my Android phone to my Arduino Uno using the HC-05 module. I also want to send data from the Arduino to my Android phone and I'm unable to do that.

Question: I will send a number from 0-9 using my android app to my Arduino Uno, the Arduino will send back the same number to my app, in words. For now, I am able to send numbers/letters to my Arduino from my app. I want help with the second part of the problem.

This is, in fact, a perfect duplicate of this question Android - receive bluetooth data from Arduino, but, unfortunately, this remains unanswered.

Answer 1

for receiving data from the arduino

UsbSerialInterface.UsbReadCallback mCallback = new UsbSerialInterface.UsbReadCallback() { 
     //Defining a Callback which triggers whenever data is read.
        @Override
        public void onReceivedData(byte[] arg0) {
            String data = null;
            try {
                data = new String(arg0, "UTF-8");
                data.concat("/n");
                tvAppend(textView, data);
            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
            }
        }
    };

and to send data from the arduino

serialPort.write(string.getBytes()); 

check the full tutorial