如何区分翻译不存在或翻译是否与源相同？

Question

I am using QCoreApplication::translate() to translate text.

I am trying to understand whether a string has a translation.

Qt documentation states:

If none of the translation files contain a translation for sourceText in context, this function returns a QString equivalent of sourceText .

The problem I am facing is that I am getting results similar to this:

<message>
    <source>Side</source>
    <translation>Side</translation>
</message>

Where source and translation are the same.

In many languages, the translation is indeed same as the source. But if translate("Side") returns "Side" , I can't tell whether the translation was exactly "Side" or whether the translation was empty.

How can I differentiate between the two cases?

Answer 1

AFAIK there is no way to differentiate between the two cases through a QTCoreApplication::translate call.

However, QTranslator::translate returns a null QString when the key is not found (Qt 5). So one option would be to keep a container around with every QTranslator you've added through installTranslator() (since QCoreApplication doesn't have a way to get those back). Then, loop through that container, calling QTranslator::translate() on each instance in the container. When you get a non-empty result, you found a translation; if no translator succeeded, then you know the key doesn't exist in any QTranslator you have.

psuedo-code:

bool hasTranslation(const char* key)
{
  QString result;
  if(!translators.size())
    return false;

  for(const auto& translator : translators)
  {
    result = translator->translate("context", key);
    if(!result.isNull())
      break;
  }
  return !result.isNull();
}

Answer 2

AFAIK, there is no way. The translate function works in the following way: it iterates over all the translators that are available for the application, and tries to translate the source text with each of them. If it succeeds, it immediately breaks out of the loop and returns the translated text. If the aforementioned loop has finished, but the translation has not been found, it returns the source text in a form of a QString:

QString QCoreApplication::translate(const char *context, const char *sourceText,
                                    const char *disambiguation, Encoding encoding, int n)
{
    QString result;

    if (!sourceText)
        return result;

    if (self && !self->d_func()->translators.isEmpty()) {
        QList<QTranslator*>::ConstIterator it;
        QTranslator *translationFile;
        for (it = self->d_func()->translators.constBegin(); it != self->d_func()->translators.constEnd(); ++it) {
            translationFile = *it;
            result = translationFile->translate(context, sourceText, disambiguation, n);
            if (!result.isEmpty())
                break;
        }
    }

    if (result.isEmpty()) {
#ifdef QT_NO_TEXTCODEC
        Q_UNUSED(encoding)
#else
        if (encoding == UnicodeUTF8)
            result = QString::fromUtf8(sourceText);
        else if (QTextCodec::codecForTr() != 0)
            result = QTextCodec::codecForTr()->toUnicode(sourceText);
        else
#endif
            result = QString::fromLatin1(sourceText);
    }

    replacePercentN(&result, n);
    return result;
}

If you really need to be able to know if the translation could be found, you would have to subclass QTranslator class and override it's translate() function (since the translate() in QCoreApplication is non-virtual).