Here we are adding the buttons to force serial-connection related functions.

MainActivity.java

//-------------------------------
        //Serial Connection Functions
        //----------------------

        usbManager = (UsbManager) getSystemService(this.USB_SERVICE);
        startButton = (Button) findViewById(R.id.buttonStart);
        sendButton = (Button) findViewById(R.id.buttonSend);
        orderButton = (Button) findViewById(R.id.btnorder);
        clearButton = (Button) findViewById(R.id.buttonClear);
        stopButton = (Button) findViewById(R.id.buttonStop);
        editText = (EditText) findViewById(R.id.editText);
        textView = (TextView) findViewById(R.id.textView);
        setUiEnabled(false);
        IntentFilter filter = new IntentFilter();
        filter.addAction(ACTION_USB_PERMISSION);
        filter.addAction(UsbManager.ACTION_USB_DEVICE_ATTACHED);
        filter.addAction(UsbManager.ACTION_USB_DEVICE_DETACHED);
        registerReceiver(broadcastReceiver, filter);