/** Private method invoking fields validation */
  private boolean validateFields() {
    boolean validated = true;

    if (!mNumberTextField.isValidCardNumber()) {
      mNumberTextField.setBackgroundResource(R.drawable.textfield_search_empty_pressed);
      validated = false;
    }
    if (!mCVCTextField.isValidCVCNumber(mNumberTextField.getType())) {
      mCVCTextField.setBackgroundResource(R.drawable.textfield_search_empty_pressed);
      validated = false;
    }
    if (!mExpMonthTextField.isValidMonth()) {
      mExpMonthTextField.setBackgroundResource(R.drawable.textfield_search_empty_pressed);
      validated = false;
    }
    if (!mExpYearTextField.isValidDate(mExpMonthTextField.getMonth())) {
      mExpYearTextField.setBackgroundResource(R.drawable.textfield_search_empty_pressed);
      mExpMonthTextField.setBackgroundResource(R.drawable.textfield_search_empty_pressed);
      validated = false;
    }

    return validated;
  }
 /** Private method used to reset fields */
 private void resetErrors() {
   mNumberTextField.setBackgroundResource(android.R.drawable.edit_text);
   mCVCTextField.setBackgroundResource(android.R.drawable.edit_text);
   mExpMonthTextField.setBackgroundResource(android.R.drawable.edit_text);
   mExpYearTextField.setBackgroundResource(android.R.drawable.edit_text);
 }