C++/(Qt) pointer to any object with specific method

Question

How do I do to call a specific method present on all classes from an other (TranslationManager) class ? I simplified a lot the code. I just want to call the setTranslationText of any class from TranslationManager.

These are to take in consideration:

All classes have a setTranslationText method

We should call setTranslationText of any class from TranslationManager by using the pointer to the class

class Interface
{
   ...
   public:
     void setTranslationText(QString translatedString); 
}

class AnyOtherInterface
{
   ...
   public:
     void setTranslationText(QString translatedString); 
}

...

…
Translationmanager::Translationmanager(){
   AnyClass = Interface; // Pointer to Interface Class
   AnyClass->setTranslatioNText("Text");

   AnyClass = AnyOtherInterface; // Pointer to AnyOtherInterface Class
   AnyClass->setTranslatioNText("AnotherText");
}


…

It can't be done without that method being `virtual` in a common base and `AnyClass` being a pointer to that base. — underscore_d, Apr 19 '18 at 15:22
Your code simplification is nonsense. The `Interface` and `AnyOtherInterface` classes share no common base class, thus there's no way to have one pointer point to them all (other than `void*`). You'll have to make the simplification work, and ensure that base classes and method signatures are exact. For example `method(QString foo)` is silly, you should have `method(const QString &foo)` — Kuba hasn't forgotten Monica, Apr 19 '18 at 23:46
@KubaOber I really have basics knowledge on C++ (I would like to know more about it). If you have an online C++ course, be free to share — Dardan Iljazi, Apr 22 '18 at 18:22

score 5 · Answer 1 · edited Apr 19 '18 at 23:47

You could use a template

template <typename T>
void setTranslationText(T* t, const QString &translatedString)
{
    t->setTranslationText(translatedString);
}

That way you wouldn't need an interface class just to inherit for this one (or however many) methods. Then the template would only compile if for a given class instantiation they had a setTranslationText method defined. The way you'd use it is

Translationmanager::Translationmanager()
{
    setTranslationText(Interface, "Text");                // Pointer to Interface Class    
    setTranslationText(AnyOtherInterface, "AnotherText"); // Pointer to AnyOtherInterface Class
}

score 1 · Answer 2 · answered Apr 19 '18 at 23:50

Adding to Cory's answer: If you're using C strings to initialize QString, you shouldn't depend on the implicit conversion - instead, make your use case explicit:

template <typename T>
void setTranslationText(T* t, const char *translatedString) {
  t->setTranslationText(QString::fromUtf8(translatedString));
}

score 0 · Accepted Answer · answered Apr 22 '18 at 18:19

I wasn't precise about what I wanted. I finally found the best solution to my problem: callback.

Solution found on: C++ class member callback simple examples

std::vector<std::function<void(std::string,std::string)>> callbacks;

template<class T> void addTranslationText(T* const object, void(T::* const mf)(std::string,std::string)){
    using namespace std::placeholders;
    callbacks.emplace_back(std::bind(mf, object, _1, _2));
}

...

// Call callback
callbacks.at(0)(std::string("arg1"), std::string("arg2"));

C++/(Qt) pointer to any object with specific method

3 Answers3