I've written the following code that works fine if you decide to scan a QR code (using zxing) and store it in private storage but in case you decide to cancel scanning, it crashes and the file previously stored content disappears.

I think it might be a design error, not sure why.

Below is relevant code

...

/**
 * menu generation
 */
@Override
public boolean onCreateOptionsMenu(Menu menu) {
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.menu, menu);
    return true;
}

/**
 * menu handling
 */
@Override
public boolean onOptionsItemSelected(MenuItem item) {
    Context context = getApplicationContext();
    Toast toast = Toast.makeText(context, "", Toast.LENGTH_LONG);
    toast.setGravity(Gravity.FILL_HORIZONTAL, 0, 0);
    switch (item.getItemId()) {
        case R.id.qrScan:
            IntentIntegrator integrator = new IntentIntegrator(this);
            integrator.initiateScan();
            return true;
        case R.id.qrReset:
            File dir = getFilesDir();
            File file = new File(dir, qrCodeFile);
            boolean deleted = file.delete();
            return true;
        case R.id.appClose:
            this.finish();
            return true;
        default:
            return super.onOptionsItemSelected(item);
    }
} 

...

    public void onActivityResult(int requestCode, int resultCode, Intent intent) {
    IntentResult scanResult = IntentIntegrator.parseActivityResult(requestCode, resultCode, intent);
    Context context = getApplicationContext();
    Toast toast = Toast.makeText(context, "", Toast.LENGTH_SHORT);
    if (scanResult != null) {
        FileOutputStream fos = null;
        CharSequence text = scanResult.getContents();
        try {
            fos = openFileOutput(qrCodeFile, Context.MODE_PRIVATE);
            try {
                fos.write(text.toString().getBytes());
                fos.close();
                toast.setGravity(Gravity.FILL_HORIZONTAL, 0, 0);
                toast.setText("Code saved");
                toast.show();
            } catch (IOException ex) {
                toast.setGravity(Gravity.FILL_HORIZONTAL, 0, 0);
                toast.setText("Invalid code");
                toast.show();
                Logger.getLogger(MainActivity.class.getName()).log(Level.SEVERE, null, ex);
            }
        } catch (FileNotFoundException ex) {
                toast.setGravity(Gravity.FILL_HORIZONTAL, 0, 0);
                toast.setText("Error while saving");
                toast.show();
            Logger.getLogger(MainActivity.class.getName()).log(Level.SEVERE, null, ex);
        }
    }   else {
        toast.setGravity(Gravity.FILL_HORIZONTAL, 0, 0);
        toast.setText("Invalid code");
        toast.show();           
    }  
}