Android app not synchronized with Arduino Serial communication

Question

I have a simple sonar arduino project so that it prints the distance every second. I have implemented an android app using UsbSerial to communicate with my arduino. So far so good, I am able to receive data and the data I receive is correct, but the problem is that the values are sometimes not properly sent. Here is the sample output I receive:

data: 7
data: 1    
data: 
data: 71

and here is the code that generates output:

private UsbSerialInterface.UsbReadCallback mCallback = new UsbSerialInterface.UsbReadCallback() {

        @Override
        public void onReceivedData(byte[] arg0)
        {
            try {
                String data = new String(arg0, "UTF-8");
                System.out.println("data: " + data);
            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
            }
        }
    };

So in my opinion there is 2 problems here:

• Lines 1 & 2 must be just one line with the value of 71
• Line 3 should not exists as my application is listening onReceivedData and arduino always send something.

Any help would be much appreciated.

Answer 1

I have found a solution for the issue. by reading this link I noticed that I need to do some manipulation on the data I receive in the onReceivedData method. So I changed the mCallBack as follow:

private UsbSerialInterface.UsbReadCallback mCallback = new UsbSerialInterface.UsbReadCallback() {

        @Override
        public void onReceivedData(byte[] arg0)
        {
            if(arg0!= null && arg0.length > 0){
                if (isStartByte(arg0[0])) {
                    printData();
                    clearBytes();
                }
                appendBytes(arg0);
            }
        }
    };

and here is the other methods I added:

    private void clearBytes(){
        buffer=new byte[8];
        bufferSize = 0;
    }

    private void appendBytes(byte[] buf){
        System.arraycopy(buf, 0, buffer, bufferSize, buf.length);
        bufferSize += buf.length;
    }

    private void printData() {
        if (bufferSize == 0) {
            return;
        }
        byte[] buf = new byte[bufferSize];
        System.arraycopy(buffer, 0, buf, 0, bufferSize);

        String data = null;
        try {
            data = new String(buf, "UTF-8");
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
        if (null != data && !data.isEmpty()) {
            System.out.println("data: " + data);
        }
    }

    public boolean isStartByte(byte firstChar){
        return firstChar=='A';
    }

And also I modified the Arduino code and added character A to the beginning of the serial output. This solves the issue, however I think this is not the best practice. I think the UsbSerial library should provide better output handling( or maybe I am wrong and this is the nature of working with serial communication ).