tr() with binding: how to get the calling classname to a function,

themts

Hey guys,

I want to be able to switch my application-language on runtime to another language.
The QML part works out of the box via retranslate() but I have several c++ data-models which are not updating.

To keep things clean, I would like to create a method like tr() which takes 3 parameters, which I could call like this:

trExt("myText", &targetObject, &TargetClass::setName);

So internally something like this should happen (Attention this is NOT a working function it is just a draft of an idea):

template <typename Func>
void trExt(const QString &text, typename QtPrivate::FunctionPointer<Func>::Object *receiver, Func slot) {
  QMetaObject::invokeMethod(receiver, slot, Q_ARG(QString, text);

  connect(&languageChanger(), &LanguageChanger::languageChanged, [&]() {  
    QString newText = QCoreApplication::translate(char* NAME OF CALLING CLASS, text);
    QMetaObject::invokeMethod(receiver, slot, Q_ARG(QString, newText);
  }
}

To be able to use QCoreApplication::translate() correctly I have to forward the calling classname somehow as a context.
I have no idea how this can be done. Somehow the default tr() function is able to do it but I don't know how (magic ? ).
I would also like to avoid passing the calling context-name as an additional parameter.

Any idea?
THX

Christian Ehrlicher

It's not QObject::tr() but <YourObjectWithQ_OBJECT_macro>::tr() and therefor the class name is known and can be passed to QCoreApplication::translate()

themts

@Christian-Ehrlicher ahhh, ok. That makes sense.
So the best approach would be to put it in a macro.

SGaist

Hi,

Out of curiosity, why do you want to translate a class name ?

themts

I don’t want to translate the classname.
I want to connect a translation to a slot.
Normally I have situations like:
object.setName(tr(„super english text“))

Problem is that in this situations a retranslate wouldn’t trigger a new „setName“.

So my idea is to have a function
trExt("super english text", &object, &Class::setName);

That way it would call setName and create a connection to a languageChanged event which resets the parameter to the new translation every time

Christian Ehrlicher

@SGaist said in tr() with binding: how to get the calling classname to a function,:

why do you want to translate a class name ?

No, he wants not translate the class name but mimic tr() which in fact calls QCoreApplication::translate() where the context is the class name.

themts

one additional question:
how do I invoke a methode without the name? Or how do I get the name

I have this:

#define N_TRANSLATE\
template <typename Func>\
void trExt(const QString &text, typename QtPrivate::FunctionPointer<Func>::Object *receiver, Func slot) {\
    QMetaObject::invokeMethod(receiver, "HERE I NEED A NAME", Q_ARG(QString, text));\

To use "invokeMethod" I need the slotname.
I would like to pass the slot as shown. Can I get the name somehow? Or is there another way of invoking this slot?

Christian Ehrlicher

@themts said in tr() with binding: how to get the calling classname to a function,:

how do I invoke a methode without the name?

I don't understand what you mean - when you want to call a function you should know it's name, or?

themts

That is my function:

    template <typename Func>
        void trExt(const char *text, typename QtPrivate::FunctionPointer<Func>::Object *receiver, Func slot) {   
            const char* className = metaObject()->className();
      
            //A) CALL "Func slot" HERE AND PASS tr(text) as parameter to "Func slot"
    
            connect(&_langLoader(), &NLanguageLoader::languageChanged, [className, text, slot]() {  
                QString newText = QCoreApplication::translate(className, text);  
                //B) INVOKE METHOD "Func slot" HERE AND PASS newText as parameter to "Func slot" like QMetaObject::invokeMethod to be sure it is threadsafe  
            });
    
        }

I' missing two things now:
A) how do i call the slot (parameter 3) of the receiver? I would have exptected to use only slot(tr(text)) but compiler tells me "there is no function that takes 1 argument". Just from c++ side I would have expected that it works.

B) as the thread-context might be different I would like to use the QMetaObject::invokeMethod function as it will send it to the event loop if the target is in another context.

themts

I just checked to code of QTimer::singleShot(), which does exactly what I need.
I just have to pass 0ms.

EDIT: not completely. A singleShot does not accept arguments. It's using QMetaObject::InvokeMethodImpl() which does not take arguments...

themts

ok, I will give up...

I will do it like this.
Instead of calling

trExt("super english text", &object, &Class::setName);"

I will call

trExt("super english text", &object, "setName");

I would have prefered the first way but I'm not that deep in the Qt internals.

    void trExt(const char *text, QObject *receiver, const char *member) {
        QMetaObject::invokeMethod(receiver, member, Q_ARG(QString, tr(text)));

        const char* className = metaObject()->className();
        connect(&_langLoader(), &NLanguageLoader::languageChanged, [className, text, receiver, member]() {
            QString newText = QCoreApplication::translate(className, text);
            QMetaObject::invokeMethod(receiver, member, Q_ARG(QString, newText));
        });
    }

SGaist

What about implementing the changeEvent method to handle your object's translatable strings like shown in the dynamic translation part of the internationalization documentation ?