How to use Qt translations directly with Qapplication::tr()

Question

In an application developed in Qt I have a non-visual class (i.e., that is not inherited from a QWidget) but that handles text strings that must be presented to the user. To use the Qt translation engine, I set all strings using the function QApplication::tr().

Strings are correctly displayed in the tool Linguist, in the context of QApplication (as expected - see image below). However, when I see code I change the Locale of the application, only the strings under the context of MainWindow are amended.

The code I use to change the language is as follows::

void MainWindow::setLocale(QString sLocale)
{
    QTranslator *pTranslator = m_mpTranslators[sLocale];
    if(pTranslator)
    {
        for(map<QString, QTranslator*>::iterator it = m_mpTranslators.begin(); it != m_mpTranslators.end(); ++it)
        {
            qApp->removeTranslator(it->second);
            QApplication::removeTranslator(it->second); // Essa linha não existia antes!
        }
        qApp->installTranslator(pTranslator);
        QApplication::installTranslator(pTranslator);  // Essa linha também não!

        if(sLocale == "pt_BR")
            m_pLocaleButton->menuAction()->setIcon(QIcon(":/resources/icons/pt_BR"));
        else
            m_pLocaleButton->menuAction()->setIcon(QIcon(":/resources/icons/en_UK"));

        ui->retranslateUi(this);
        updateUI();
    }
}

I think it is important to note that the change of the texts in the graphical interface is immediate (via calls for ui->retranslateUi(this) and updateUI()), but calls from non-visual class occur later the change of the locale, then the text should be translated correctly.

In the code above, I also came to include the lines marked with comments, but this did not make the translation follow the locale defined.

Does anyone have any idea where I might be mistaken?

Editing:

The version of Qt is 5.1.0 (32 bit), and I am running on Windows 7 (64 bit). Translators are created in the class constructor MainWindow, as follows:

// Setup the translation system
QTranslator *pPortuguese = new QTranslator(this);
QString sPortuguese = QCoreApplication::applicationFilePath().replace(".exe", "_pt_BR.qm");
if(pPortuguese->load(sPortuguese))
    m_mpTranslators.insert(map<QString, QTranslator*>::value_type(QString("pt_BR"), pPortuguese));
else
    qWarning() << "Portuguese translation file not found";

QTranslator *pEnglish = new QTranslator(this);
QString sEnglish = QCoreApplication::applicationFilePath().replace(".exe", "_en_UK.qm");
if(pEnglish->load(sEnglish))
    m_mpTranslators.insert(map<QString, QTranslator*>::value_type(QString("en_UK"), pEnglish));
else
    qWarning() << "English translation file not found";

The m_mpTranslators attribute is a simple map that relates the locale string to the translator: std::map<QString, QTranslator*> m_mpTranslators;

Answer 1

The problem actually stemmed from a flaw (my mistake, Sorry!) in updating the translation files (*.qm) in the build’s target directory. In the file. pro there were no instructions for the automated copy of the translations to the destination directories, and so the tests used an earlier version of the translations (which I had manually copied, probably). This resulted in incorrect text display regardless of the context used.

To solve the problem definitely, i changed the . pro file to include in the release and debug settings the automated copy of the files to the directories correct:

. . .

copyfiles.commands += @echo Copying translation files... &

# Configurações para Windows
win32{

    . . .

    # Troca '/' por '\' nos diretórios de origem e destino
    SOURCE_WIN = $${PWD}
    SOURCE_WIN ~= s,/,\\,g
    TARGET_WIN = $${OUT_PWD}
    TARGET_WIN ~= s,/,\\,g

    debug_and_release {
        CONFIG -= debug_and_release
        CONFIG += debug_and_release
    }

    # Configurações de debug
    CONFIG(debug, debug|release) {
        CONFIG -= debug release
        CONFIG += debug

        . . .

        copyfiles.commands += @call copy $${SOURCE_WIN}\\*.qm $${TARGET_WIN}\\debug\\
    }

    # Configurações de release
    CONFIG(release, debug|release) {
        CONFIG -= debug release
        CONFIG += release

        . . .

        copyfiles.commands += @call copy $${SOURCE_WIN}\\*.qm $${TARGET_WIN}\\release\\
    }

}

# Inclui os comandos de cópia das traduções na execução do QMake
QMAKE_EXTRA_TARGETS += copyfiles
POST_TARGETDEPS += copyfiles

. . .

Answer 2

I use an older version, but from what I understand, the call from TR in your class is wrong.

The documentation says that if your class is not sub-class of QObject, use TR of QCoreApplication:

If the quoted text is not in a Member Function of a Qobject subclass, use either the tr() Function of an appropriate class, or the Qcoreapplication::Translate() Function directly

The point is: in what way you call her? Below is the example of the documentation:

 qApp->translate("LoginWidget", "Password:"),
             logwid);

I find it interesting that this example above should use an instance of QApplication, and he uses translate instead of TR.