Regarding to Abstract (or) factory pattern design with Qt.

[U7Development]

Hello..!

my current interface for creating widgets in my program is this following:

This is my factory superclass

class wmaster : public QDialog{
     Q_OBJECT

private:
     std::vector<QWidget*> vQWidgets;

protected:
     QLabel* setup_QLabel(QString _txt, QString _stylesheet);
     QLineEdit* setup_QLineEdit(QString _ph);
     QPushButton* setup_QPushbutton(QString _txt, QString _stylesheet);
     
     //etc... 

public:
     explicit wmaster(QWidget* parent = nullptr);
     ~wmaster();
};

//wmaster.cpp

wmaster::wmaster(QWidget* parent) : QDialog(parent){ }
wmaster::~wmaster(){
     for (auto& o : vQWidgets) delete o; o = nullptr;
}

QLabel* wmaster::setup_QLabel(QString _txt, QString _stylesheet){
     QLabel* o = new QLabel(this);
     o->setText(_txt);
     o->setStyleSheet(_styleSheet);
    vQWidgets.push_back(o);
    return o;
}
//same algorithm for QPushButton and QLineEdit

---

This is the login window which inherits from wmaster factory:

class wlogin : public wmaster{
private:
     QLabel* lblName {nullptr};
     QLineEdit* ledName {nullptr};
     QPushButton* pbtLogin {nullptr};

public:
     explicit wlogin(QWidget* parent = nullptr);
};

//wlogin.cpp

wlogin::wlogin(QWidget* parent) : wmaster(parent) {
      //initialization
      lblName = setup_QLabel("Username", C_STYLESHEET_LABEL);  //C_STYLESHEET_LABEL constant as QString
      ledName = setup_QLineEdit("Please input here your username...");
      pbtLogin = setup_QPushButton("Click here to login", C_STYLESHEET_BTN);
      
}

This tricky factory works fine for me, but I know this is not the best approach to inherit factory...
I was reading an article that explains abstract factory, but I don't see how can I apply to QWidget classes.. since the article explains that I need to create an abstract object for each of my instantiated objects... and I guess I don't need to create an abstract class for QLabel for example.
https://refactoring.guru/es/design-patterns/abstract-factory/cpp/example

Is it recommended to follow abstract factory to create QWidget objects or what design pattern should I follow?
thanks

[Christian Ehrlicher]

I don't see any adavantag ein using wmaster here. Why do you think you need it?

[U7Development]

Since my program has more windows, all of them initialize their member QWidgets from their respective constructor and all of them make the call to wmaster factory with the setup_ method... this helps me to write less on constructors.

Inherits from wmaster is trivial, just curious about if it is the sane way or there is another way I can follow...

[Christian Ehrlicher]

@U7Development said in Regarding to Abstract (or) factory pattern design with Qt.:

 QLabel* o = new QLabel(this);
 o->setText(_txt);
 o->setStyleSheet(_styleSheet);

So you want to move those three (basically only one, the stylesheet can be set on the parent and all is fine) lines into a separate function?
Where do you set up the layouting? I would guess a ui file would be much more maintainable here.

[U7Development]

@Christian-Ehrlicher
thanks for your answers..
I recently found that in the Scott Meyer's book : Effective C++ recommends to use factory as a component more than a superclass.

ui is fine, but I switched to handcoding (I am a bit capricious) because I like to implement manually my user interface. I build my whole program as this way and I'm about to finish it.. but this is the time for a refactory.

Regarding to layouts.. im not using them, all sizes are fixed and positions are preconfigured at compile time..

[Christian Ehrlicher]

@U7Development said in Regarding to Abstract (or) factory pattern design with Qt.:

Regarding to layouts.. im not using them, all sizes are fixed and positions are preconfigured at compile time..

ouch

Effective C++ recommends to use factory as a component more than a superclass.

I still don't see a reason why you need a base class for this one line - you don't gain anything apart you can say you're using a specific design pattern (and this is more or less a reason not to use it).

[SimonSchroeder]

If wmaster is a factory and wlogin inherits it this also makes wlogin a factory. That doesn't sound right that wlogin should be a factory.

Honestly, I am not an expert on many of the design patterns, so you try to read up on the things I mention. However, to me a factory class usually only has static method: You don't need a factory object and you can just call the methods to create new objects (like the QLabel). This also means that you are right that a factory should be a component and not a superclass. BTW, to make a factory a class also comes from pure OOP (like is required from Java). But, you don't actually need an object here and just want to call methods that do something. Since C++ is multiparadigm, to me personally a better approach would be to use free standing functions instead of methods for the factory. These can then be put into a namespace to clean things up a little.