gtkmm catch widget destruction event

Question

I would like to add a sigc callback to the destruction of a widget. How can I connect so that when the widget is destroyed, my callback is called? There is no such signal on Gtk::Widget. Can I do it using C API?

Note : I use gtkmm 3.24.5.

Answer 1

I have not found documentation specific to 3.24.5. However, in 3.24.4, Gtk::Widgets inherits from sigc::trackable which exposes a sigc::trackable::add_destroy_notify_callback method. It seems to be what you are looking after. Here is a quick example to show how it works (Build with Gtkmm 3.24.20):

#include <iostream>
#include <gtkmm.h>

void* DestructorCallback(void* p_in)
{
    std::cout << "Button destruction!" << std::endl;
    return nullptr;
}

class MainWindow : public Gtk::ApplicationWindow
{

public:

    MainWindow();

private:

    Gtk::Button m_button;

};

MainWindow::MainWindow()
: m_button{"Hello World!"}
{
    m_button.add_destroy_notify_callback(nullptr, DestructorCallback);
}

int main(int argc, char *argv[])
{
    auto app = Gtk::Application::create(argc, argv, "org.gtkmm.examples.base");
  
    MainWindow window;
    window.show_all();
  
    return app->run(window);
}

The documentation does not say much (in fact, it says nothing) about what is supposed to be p_in as well as the void* return value from the callback though...

Hope this works in Gtkmm 3.24.5.