Singleton pattern with gtk3 and gtkmm

Question

I'm working on a gui app with cpp and gtkmm3. In this app, some widgets require the singleton pattern to implement such as window (because i want just one window in all over the app) this is my header file:

class MyWindow : public Gtk::ApplicationWindow {

public:
    MyWindow(BaseObjectType *pWindow, Glib::RefPtr<Gtk::Builder> builder);
    ~MyWindow();
    MyWindow(MyWindow const&) = delete;
    void operator=(MyWindow const&) = delete;
    static MyWindow* getInstance();

private:
    MyWindow();

};

and source file is:

MyWindow::MyWindow(){}

MyWindow::MyWindow(BaseObjectType *pWindow, Glib::RefPtr<Gtk::Builder> refBuilder)
        : Gtk::ApplicationWindow(pWindow),
          builder(refBuilder) {

}

MyWindow::~MyWindow() {}

MyWindow *MyWindow::getInstance() {
    static MyWindow *window;
    return window;
}

my question is: Is there a more appropriate and reasonable pattern instead singleton pattern? Is using this pattern suitable for the interface widgets and gui app?

Answer 1

The major problem with the Singleton design pattern is that it gives you:

1. a single instance;
2. global access.

The single instance aspect of the singleton is what people usually are looking for (like in your case), but not global access.

The usual alternative* to this is to declare a MyWindow instance and then inject it to anyone who needs it. This is known as dependency injection . So you have something like:

void DoSomeThingOnWindow(MyWindow& p_window)
{
    p_window.DoSomething();
}

// At the beginning:
MyWindow window;

// Everywhere else:
DoSomeThingWithTheWindow(window);

instead of:

void DoSomeThingOnWindow()
{
    // Global access:
    MyWindow* window = MyWindow::getInstance();
    window->DoSomething();
}

// Everywhere:
DoSomeThingWithTheWindow();

The "bad" side of dependency injection over a singleton is that it will not enforce the single instance. However, if you use it everywhere and carefully, you can pass a single instance all around and not have global access, which will have so much more benefits.