Re: how to get key press event in goocanvasmm

I don't know anything about goocanvasmm, but I know a lot about gtkmm 
and glibmm. As far as I can see your on_key_press_event() should be 
called, provided that m_canvas has the keyboard focus. If a child of 
m_canvas has the keyboard focus, on_key_press_event() should be called 
if the child does not handle the signal. If the child handles the 
signal, and returns /true/ from its signal handler, there's no hope for you.

You can read about event signals in the gtkmm tutorial, 
https://developer.gnome.org/gtkmm-tutorial/stable/chapter-keyboardevents.html.en 
and 
https://developer.gnome.org/gtkmm-tutorial/stable/sec-xeventsignals.html.en

If on_key_press_event() is not called there's another possibility. 
Instead of overriding the default signal handler, connect another signal 
handler. (It won't do any difference if one of m_canvas's children 
handles the signal.)

bool on_canvas_key_press_event(GdkEventKey* event)
{ ....... }
MyCanvas()
{
   signal_key_press_event().connect(sigc::mem_fun(*this, 
&MyCanvas::on_canvas_key_press_event), false);
}

Note /false/ in connect().

I recommend that you replace Gtk::Main by Gtk::Application, unless you 
use a very old version of gtkmm. Gtk::Main has been deprecated since 2012.

/Kjell

On 2020-02-14 18:51, Klaus Rudolph wrote:
> Is it possible to receive key press events in canvas?
>
> The following signal handler is not called inside goocanvas. It compiles fine but it is not called if a key is pressed.
>
>
> Exmaple:
>
>
> Glib::RefPtr<Goocanvas::Item> root;
>
> class MyCanvas: public Goocanvas::Canvas
> {
>      double scale = 1;
>
>      bool on_key_press_event( GdkEventKey* event ) override
>      {
>          std::cout << "on_key_press_event" << std::endl;
>          return true;
>      }
>
> };
>
> int main(int argc, char* argv[])
> {
>      Gtk::Main app(&argc, &argv);
>      Goocanvas::init("example", "0.1", argc, argv);
>
>      Gtk::Window win;
>
>      MyCanvas m_canvas;
>      m_canvas.set_size_request(640, 480);
>      m_canvas.set_bounds(0, 0, 800, 800);
>      root = m_canvas.get_root_item();
>
>      //--------------------------------
>
>      Glib::RefPtr<Goocanvas::Ellipse> outer = Goocanvas::Ellipse::create( 100,100,20,20);
>      outer->property_line_width() = 5;
>      outer->property_stroke_color() = "red";
>      outer->property_fill_color()="blue";
>      root->add_child( outer );
>
>      win.add( m_canvas);
>      win.show_all_children();
>
>
>      Gtk::Main::run(win);
>      return 0;
> }

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