Dynamic translation (was: How to get QApplication pointer)

[MarkoSan]

Hi to all!

I have an QApplication object in which QTranslator is installed. It works perferctly. But now I have a problem. I have a "grandchild" qwidget that holds language selection QPushButton subclassed objects. How do I launch QApplication::loadTranslator from this window??

[Gopala Krishna]

Hi to all!

I have an QApplication object in which QTranslator is installed. It works perferctly. But now I have a problem. I have a "grandchild" qwidget that holds language selection QPushButton subclassed objects. How do I launch QApplication::loadTranslator from this window??

Use qApp
qApp->loadTranslator();

[MarkoSan]

Hmm, this does not work:

void CLanguageSelectorWidget::translateSlovene()
{
    m_Translator.load("translations/eROSystem_client_SL");    // loads translator
    //QApplication::installTranslator(&m_Translator);    // installs it
    qApp->installTranslator(&m_Translator);    // installs it
    emit accept();    // closes window
}

void CLanguageSelectorWidget::translateSlovene()
{
    m_Translator.load("translations/eROSystem_client_SL");    // loads translator
    //QApplication::installTranslator(&m_Translator);    // installs it
    qApp->installTranslator(&m_Translator);    // installs it
    emit accept();    // closes window
}

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Why not???

In main.cpp there is a very similar code that works:

// translator setup
    QTranslator qtTranslator;
    qtTranslator.load("translations/eROSystem_client_SL");
    a.installTranslator(&qtTranslator);

// translator setup
    QTranslator qtTranslator;
    qtTranslator.load("translations/eROSystem_client_SL");
    a.installTranslator(&qtTranslator);

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Why the upper code chunk does not work?? Signals/Slots are ok, I've checked.

[jpn]

In main() the QTranslator object remains alive because QApplication::exec() blocks until the application quits. Is CLanguageSelectorWidget allocated on the stack? The translator object goes out of scope as soon as CLanguageSelectorWidget is destructed.

[MarkoSan]

How come, if m_Translator is defined in its header file:

#ifndef CLANGUAGESELECTORWIDGET_H_
#define CLANGUAGESELECTORWIDGET_H_
 
/*!
 * \class CLanguageSelectorWidget
 * \author VSistemi Marko Frelih s.p.
 * \version 1.0
 * \date January 2007
 * \brief This Qt based class represents a language selector widget, which constist of number of
 *     CFlagButton objects.
 * \details version 1.00 (revision 84): basic functionality
*/
 
// qt includes
#include <QDialog>
#include <QHBoxLayout>
#include <QVBoxLayout>
#include <QList>
#include <QFont>
#include <QPalette>
#include <QTranslator>
#include <QApplication>
 
class QWidget;    // forward declaration
 
// custom includes
#include "CFlagButton.h"
 
class CLanguageSelectorWidget : public QDialog
{
    Q_OBJECT
 
public:
    CLanguageSelectorWidget(QWidget* pParent);
    ~CLanguageSelectorWidget();
    inline QPointer<QHBoxLayout> langaugeButtonsLayout() { return m_pLanguageButtonsLayout; };
    inline QPointer<QVBoxLayout> mainLayout() { return m_pMainLayout; };
    //inline QList<CFlagButton> languageButtonsList() { return mLanguageButtonsList; };
    inline QPalette widgetPalette() { return m_WidgetPalette; };
    inline QPointer<QPushButton> sloLangButton() { return m_pSloLangButton; };
    inline QPointer<QPushButton> ukLangButton() { return m_pUKLangButton; };
    inline QPointer<QPushButton> deuLangButton() { return m_pDeuLangButton; };
    inline QPointer<QPushButton> itaLangButton() { return m_pItaLangButton; };
 
public:
    // TODO: this member should be private
    //QList<CFlagButton> mLanguageButtonsList;    // language buttons list
 
private:
    QPointer<QHBoxLayout> m_pLanguageButtonsLayout;    // horizontal layout
    QPointer<QVBoxLayout> m_pMainLayout;    // main layouts
    QPointer<QPushButton> m_pSloLangButton;    // slo lang
    QPointer<QPushButton> m_pUKLangButton;    // eng lang
    QPointer<QPushButton> m_pDeuLangButton;    // deu lang
    QPointer<QPushButton> m_pItaLangButton;    // ita lang
    QPalette m_WidgetPalette;    // widget palette
    QTranslator m_Translator;    // application translator
 
private slots:
    void translateSlovene();    // launches slovenian translation
    void translateEnglish();    // launches english translation
    void translateDeutsch();    // launches german translation
    void translateItaliano();    // launches italian translation
};
 
#endif /*CLANGUAGESELECTORWIDGET_H_*/

#ifndef CLANGUAGESELECTORWIDGET_H_
#define CLANGUAGESELECTORWIDGET_H_

/*!
 * \class CLanguageSelectorWidget
 * \author VSistemi Marko Frelih s.p.
 * \version 1.0
 * \date January 2007
 * \brief This Qt based class represents a language selector widget, which constist of number of
 *     CFlagButton objects.
 * \details version 1.00 (revision 84): basic functionality
*/

// qt includes
#include <QDialog>
#include <QHBoxLayout>
#include <QVBoxLayout>
#include <QList>
#include <QFont>
#include <QPalette>
#include <QTranslator>
#include <QApplication>

class QWidget;    // forward declaration

// custom includes
#include "CFlagButton.h"

class CLanguageSelectorWidget : public QDialog
{
    Q_OBJECT
    
public:
    CLanguageSelectorWidget(QWidget* pParent);
    ~CLanguageSelectorWidget();
    inline QPointer<QHBoxLayout> langaugeButtonsLayout() { return m_pLanguageButtonsLayout; };
    inline QPointer<QVBoxLayout> mainLayout() { return m_pMainLayout; };
    //inline QList<CFlagButton> languageButtonsList() { return mLanguageButtonsList; };
    inline QPalette widgetPalette() { return m_WidgetPalette; };
    inline QPointer<QPushButton> sloLangButton() { return m_pSloLangButton; };
    inline QPointer<QPushButton> ukLangButton() { return m_pUKLangButton; };
    inline QPointer<QPushButton> deuLangButton() { return m_pDeuLangButton; };
    inline QPointer<QPushButton> itaLangButton() { return m_pItaLangButton; };

public:
    // TODO: this member should be private
    //QList<CFlagButton> mLanguageButtonsList;    // language buttons list

private:
    QPointer<QHBoxLayout> m_pLanguageButtonsLayout;    // horizontal layout
    QPointer<QVBoxLayout> m_pMainLayout;    // main layouts
    QPointer<QPushButton> m_pSloLangButton;    // slo lang
    QPointer<QPushButton> m_pUKLangButton;    // eng lang
    QPointer<QPushButton> m_pDeuLangButton;    // deu lang
    QPointer<QPushButton> m_pItaLangButton;    // ita lang
    QPalette m_WidgetPalette;    // widget palette
    QTranslator m_Translator;    // application translator

private slots:
    void translateSlovene();    // launches slovenian translation
    void translateEnglish();    // launches english translation
    void translateDeutsch();    // launches german translation
    void translateItaliano();    // launches italian translation
};

#endif /*CLANGUAGESELECTORWIDGET_H_*/

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[jpn]

Where do you show/exec CLanguageSelectorWidget? Consider following code:

{
    CLanguageSelectorWidget dialog(this);
    if (dialog.exec() == QDialog::Accepted)
    {
    }
} // the translator gets destructed here together with CLanguageSelectorWidget

{
    CLanguageSelectorWidget dialog(this);
    if (dialog.exec() == QDialog::Accepted)
    {
    }
} // the translator gets destructed here together with CLanguageSelectorWidget

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[MarkoSan]

So, what do you suggest, how should I recode?

[jpn]

Allocate the translator on the heap. In other words, create the translator with keyword "new". It must remain alive after the dialog gets destructed, right?

[MarkoSan]

Yes, you are right. God damn, I've forgot the basics ... I've allocated it, but same result. I think object gets destructed again after leaving QDialog:

m_pTranslator=new QTranslator(this);    // creats new translator
    Q_CHECK_PTR(m_pTranslator);    // checks creation
    m_pTranslator->load("translations/eROSystem_client_ITA");    // loads translator
    //QApplication::installTranslator(&m_Translator);    // installs it
    qApp->installTranslator(m_pTranslator);    // installs it
    emit accept();    // closes window

m_pTranslator=new QTranslator(this);    // creats new translator
    Q_CHECK_PTR(m_pTranslator);    // checks creation
    m_pTranslator->load("translations/eROSystem_client_ITA");    // loads translator
    //QApplication::installTranslator(&m_Translator);    // installs it
    qApp->installTranslator(m_pTranslator);    // installs it
    emit accept();    // closes window

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Am I right?

[jpn]

Don't pass "this" as its parent. Every QObject will automatically delete its children. Here, the dialog will delete the translator. Try passing for example "qApp" as parent instead.

[MarkoSan]

I did, still no result. Is it possible the path to translator file is corrupted??? Is it ok to use "/" in path under windows instead of "\'

[jpn]

I did, still no result. Is it possible the path to translator file is corrupted???

QTranslator::load() returns true if the translation is successfully loaded; otherwise returns false. So check the return value!

Is it ok to use "/" in path under windows instead of "\'

Yes, it's ok. Qt will translate your paths to conform to the underlying operating system.

[MarkoSan]

Here is the code:

m_pTranslator=new QTranslator(qApp);    // creats new translator
    Q_CHECK_PTR(m_pTranslator);    // checks creation
    if(m_pTranslator->load("translations/eROSystem_client_ITA"))    // loads translator
    {
        //QApplication::installTranslator(&m_Translator);    // installs it
        qApp->installTranslator(m_pTranslator);    // installs it
        emit accept();    // closes window, success    
    } else {
        emit reject();    // failure
    }

m_pTranslator=new QTranslator(qApp);    // creats new translator
    Q_CHECK_PTR(m_pTranslator);    // checks creation
    if(m_pTranslator->load("translations/eROSystem_client_ITA"))    // loads translator
    {
        //QApplication::installTranslator(&m_Translator);    // installs it
        qApp->installTranslator(m_pTranslator);    // installs it
        emit accept();    // closes window, success    
    } else {
        emit reject();    // failure
    }

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Every language button succesfully loads translator. But still no result!!!

[jpn]

Every language button succesfully loads translator. But still no result!

What does this mean? Do your widgets catch QEvent::LanguageChange?

PS. QDialog::accept() and QDialog::reject() are not signals so drop those "emits" for sake of clarity.

[jpn]

Oh, and for dynamic translation you might want to check this wiki article out: [WIKI]Dynamic translation[/WIKI]

[MarkoSan]

I've read the wiki, but what is the point of translating application using QLinguist if I must enter tr() texts MANUALY in changeEvent. And how does application know which language was changed to???

[jpn]

I've read the wiki, but what is the point of translating application using QLinguist if I must enter tr() texts MANUALY in changeEvent.

You might want to read it again, you must have missed something. If you mean text written in Designer, UIC provides a retranslateUi() method which is mentioned in the article.

And how does application know which language was changed to???

QObject::tr() and QApplication::translate() work based on installed translators.

[MarkoSan]

You might want to read it again, you must have missed something. If you mean text written in Designer, UIC provides a retranslateUi() method which is mentioned in the article.


QObject::tr() and QApplication::translate() work based on installed translators.

I do not use Designer, all my classes are handcoded.

[jpn]

So what's the problem? Everything in your code marked for translation (QObject::tr(), QApplication::tr(), etc.) is shown in Linguist. Let's say you write strings in code in English. You already have English version of your app without providing any translations. In Linguist you write translations to other languages.

Edit: Oh, I think I just understood what you meant. No, you don't pass translated version to QObject::tr() and co. The whole point is to keep it for example English only in code and with help of tr() you get automatically provided the translation from installed translators. You just have to reset translatable strings when the language changes.

[MarkoSan]

But I have Slovenian version in code. Then I've made 4 .ts files:
- copy of Slovenian translation
- English
- Deutsch
- Italiano

Now, I smply do not know what to put in retranslate() function. All other things are getting clear now.