Dynamic translation (was: How to get QApplication pointer)

[jpn]

Then just keep all the strings in code Slovenian. Sorry, but I don't understand what in this concept is it so hard to understand. Once you have installed a German translator, QObject::tr("some Slovenian text") will return the text in German, provided that the particular string was translated.

[MarkoSan]

Ok, but I still do not get what do I have to implement in retranslate() function. I just set arbitrary tr() strings in it then if, for instance, german translator is automatically loaded?

[jpn]

It's YOU who installs the translator:

// <no translator installed>
qDebug() << tr("slovenian text"); // outputs "slovenian text" in slovenian
 
qApp->installTranslator(germanTranslator);
qDebug() << tr("slovenian text"); // outputs "slovenian text" in german
 
qApp->installTranslator(italianTranslator);
qDebug() << tr("slovenian text"); // outputs "slovenian text" in italian

// <no translator installed>
qDebug() << tr("slovenian text"); // outputs "slovenian text" in slovenian

qApp->installTranslator(germanTranslator);
qDebug() << tr("slovenian text"); // outputs "slovenian text" in german

qApp->installTranslator(italianTranslator);
qDebug() << tr("slovenian text"); // outputs "slovenian text" in italian

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Now, lets take a QLabel holding a string as an example. QLabel does not automatically translate anything because it doesn't make any sense. First of all, not all strings all translated and secondly, it would add unnecessary overhead. Every widget receives a language change event when language changes. This is the point when you have to ract. You must catch the event and reset all strings you want to translate in current language.

// this will create a new label with string "slovenian text" in current language, whatever the current translator happens to be
QLabel* label = new QLabel(tr("slovenian text"));
 
// later on, you switch the language by installing another translator
// the label introduced above will not react anyhow, you will have to catch the event and do it yourself
// this time, QObject::tr() returns the same string in different language, in language which was just installed
void SomeWindow::changeEvent(QEvent* event)
{
    if (event->type() == QEvent::LanguageChange)
        label->setText(tr("slovenian text"));
}

// this will create a new label with string "slovenian text" in current language, whatever the current translator happens to be
QLabel* label = new QLabel(tr("slovenian text"));

// later on, you switch the language by installing another translator
// the label introduced above will not react anyhow, you will have to catch the event and do it yourself
// this time, QObject::tr() returns the same string in different language, in language which was just installed
void SomeWindow::changeEvent(QEvent* event)
{
    if (event->type() == QEvent::LanguageChange)
        label->setText(tr("slovenian text"));
}

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[Gopala Krishna]

@admins: would it possible to rename this helpful thread to what exactly it reflect ?

Sorry for being offtopic.

[NTwoO]

I use dynamic translation extensively in my application.

The way I solved the problem is by inheriting QApplication to MyApp.

In the header of MyApp I have a list of QTranslator members for each language/locale. In MyApp I also have a ChangeLang(LangEnum LANG) function.

This will load the chosen language.

In MyApp I have some strings that are application wide specific (eg: translation of the days of the week or the months) Open windows get an event as described in the helpfile at Trolltech.

MyApp is accessed as

MyApp* locApp= (MyApp*)qApp;
locApp->LoadLanguage(ENG);//loads english
locApp->LoadLanguage(NLD);//loads Dutch
locApp->LoadLanguage(ZHO);//loads Mandarin

MyApp* locApp= (MyApp*)qApp;
locApp->LoadLanguage(ENG);//loads english
locApp->LoadLanguage(NLD);//loads Dutch
locApp->LoadLanguage(ZHO);//loads Mandarin

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void MyApp::ChangeLang(LangEnum LANG)
{
	if(lang!=CurLang)
	{
		CurLang=lang;
		//Ensure that we have no translation loaded
		removeTranslator(&SPAtran);
		removeTranslator(&ENG_AUtran);
		removeTranslator(&DEUtran);
		removeTranslator(&FRAtran);
		removeTranslator(&NLDtran);
		removeTranslator(&ZHOtran);
		removeTranslator(&PORtran);
		removeTranslator(&ENG_UStran);
		removeTranslator(&ENGtran);
		switch(lang)
		{
			case ENGLISH:
#ifdef VER_US
				installTranslator(&ENG_UStran);
#elif	defined(VER_AU)
				installTranslator(&ENG_AUtran);
#elif	defined(VER_UK)
				installTranslator(&ENGtran);
#else
				installTranslator(&ENGtran);
#endif
				break;
			case GERMAN:
				installTranslator(&DEUtran);
 
				break;
			case DUTCH:
				installTranslator(&NLDtran);
				break;
			case SPANISH:
				installTranslator(&SPAtran);
				break;
			case FRENCH:
				installTranslator(&FRAtran);
				break;
			case MANDARIN:
				installTranslator(&ZHOtran);
				break;
			case ITALIAN:
			//Not defined
				break;
			case GREEK:
			//Not defined
				break;
			case PORTUGESE:
				installTranslator(&PORtran);
				break;
			case UNINITIALISED:
			default:
				break;
		}
		if(MANDARIN==lang)
		{
		 	CentralFont.setFamily( "mandarin" );
		}
		else
		{
		 	CentralFont.setFamily( "Freesans" );
		}
		MyCurSet.LoadPresentations();
		langInit();
		FillEditLists();
		emit newLang();
 
	}
}

void MyApp::ChangeLang(LangEnum LANG)
{
	if(lang!=CurLang)
	{
		CurLang=lang;
		//Ensure that we have no translation loaded
		removeTranslator(&SPAtran);
		removeTranslator(&ENG_AUtran);
		removeTranslator(&DEUtran);
		removeTranslator(&FRAtran);
		removeTranslator(&NLDtran);
		removeTranslator(&ZHOtran);
		removeTranslator(&PORtran);
		removeTranslator(&ENG_UStran);
		removeTranslator(&ENGtran);
		switch(lang)
		{
			case ENGLISH:
#ifdef VER_US
				installTranslator(&ENG_UStran);
#elif	defined(VER_AU)
				installTranslator(&ENG_AUtran);
#elif	defined(VER_UK)
				installTranslator(&ENGtran);
#else
				installTranslator(&ENGtran);
#endif
				break;
			case GERMAN:
				installTranslator(&DEUtran);

				break;
			case DUTCH:
				installTranslator(&NLDtran);
				break;
			case SPANISH:
				installTranslator(&SPAtran);
				break;
			case FRENCH:
				installTranslator(&FRAtran);
				break;
			case MANDARIN:
				installTranslator(&ZHOtran);
				break;
			case ITALIAN:
			//Not defined
				break;
			case GREEK:
			//Not defined
				break;
			case PORTUGESE:
				installTranslator(&PORtran);
				break;
			case UNINITIALISED:
			default:
				break;
		}
		if(MANDARIN==lang)
		{
		 	CentralFont.setFamily( "mandarin" );
		}
		else
		{
		 	CentralFont.setFamily( "Freesans" );
		}
		MyCurSet.LoadPresentations();
		langInit();
		FillEditLists();
		emit newLang();

	}
}

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The translations are removed before loading a new one. The documentation has nothing about reloading an already loaded translation, so out of memory paranoia I simply remove all that is not used and load the one I use.

The header looks something like

typedef enum _LangEnum
{//This enum must match the enum in the SGCP document
	UNINITIALISED=-1,
	ENGLISH=0,
	GERMAN,
	DUTCH,
	SPANISH,
	FRENCH,
	MANDARIN,
	ITALIAN,
	GREEK,
	PORTUGESE
} LangEnum;
class MyApp : public QApplication
{
    Q_OBJECT
 
	public:
	QFont CentralFont;
	LangEnum CurLang;
	QTranslator	SPAtran;
	QTranslator	ENGtran;
	QTranslator	ENG_AUtran;
	QTranslator	DEUtran;
	QTranslator	FRAtran;
	QTranslator	NLDtran;
	QTranslator	ZHOtran;
	QTranslator	PORtran;
	QTranslator	ENG_UStran;
	void ChangeLang(LangEnum lang);
	signals:
	void newLang();
}

typedef enum _LangEnum
{//This enum must match the enum in the SGCP document
	UNINITIALISED=-1,
	ENGLISH=0,
	GERMAN,
	DUTCH,
	SPANISH,
	FRENCH,
	MANDARIN,
	ITALIAN,
	GREEK,
	PORTUGESE
} LangEnum;
class MyApp : public QApplication
{
    Q_OBJECT
		
	public:
	QFont CentralFont;
	LangEnum CurLang;
	QTranslator	SPAtran;
	QTranslator	ENGtran;
	QTranslator	ENG_AUtran;
	QTranslator	DEUtran;
	QTranslator	FRAtran;
	QTranslator	NLDtran;
	QTranslator	ZHOtran;
	QTranslator	PORtran;
	QTranslator	ENG_UStran;
	void ChangeLang(LangEnum lang);
	signals:
	void newLang();
}

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As you can see this version also switches fonts for writing mandarin. Looks really neat! Our customers are very impressed! The planning of the competition also took a speedbump with this nice little extra.

[MarkoSan]

Well, I've done it. Thanks to all that helped me. I now even can support dynamic number of languages. I have a list of languages in mysql database table. I load it at runtime an then the magic works!!!

[Nippler]

Well, I've done it. Thanks to all that helped me. I now even can support dynamic number of languages. I have a list of languages in mysql database table. I load it at runtime an then the magic works!!!

How have you done it?
At the moment I am working exactly on this problem!

Thanks for an answer.

[jpn]

How have you done it?
At the moment I am working exactly on this problem!

Did you read the wiki article: [WIKI]Dynamic translation[/WIKI]?