Hello,
I have a custom widget that I've implemented in C and then used gmmproc[1]
to generate C++ bindings for that widget. The process was mostly smooth,
but I cannot seem to use my generated C++ bindings in
Gtk::Builder::get_widget. I can post the full source code if needed, but
probably there is something simple that I a missing so I'll start with what
I think is most relevant:
My widget is a relatively simple extension of GtkDrawingArea which adds the
ability to pan and zoom using mouse motion and mouse wheel. It's called
GtkPanZoomArea. I have created a Glade catalog XML file which allows me to
use my custom widget in glade. I have successfully used my widget in an
application using the plain-C API, retrieving a pointer to an instance of
this widget like so:
~~~
GtkPanZoomArea* panzoom_ =
GTK_PANZOOM_AREA(builder->get_object("overhead-view")->gobj());
~~~
I have gone through the process of using `h2def.py` and `enum.py`, and
written a custom `gen_extra_defs.cc` (using `glibmm_generate_extra_defs`)
to generate def files, and I have used `gmmproc` to generate the `mm-`
wrapper `Gtk::PanZoomArea`.
Everything compiles, but when I change the above code to:
~~~
Gtk::PanZoomArea panzoom_;
builder->get_widget("overhead-view", panzoom_)
~~~
the member is assigned nullptr and I see the following errors printed to
stderr:
~~~
: CRITICAL **: 13:53:12.873: Gtk::Builder::get_widget(): dynamic_cast<>
failed.
~~~
The following works:
~~~
Gtk::DrawingArea* drawingarea;
builder->get_widget("overhead-view", drawingarea);
~~~
But then this subsequently does not work:
~~~
auto panzoom_ = dynamic_cast<Gtk::PanZoomArea*>(drawingarea);
~~~
My guess is that the most likely place for there to be an error is in the
`.hg` file so here is the class declaration I have in `mm/panzoomarea.hg`:
~~~
class PanZoomArea : public Gtk::DrawingArea {
_CLASS_GOBJECT(PanZoomArea, GtkPanZoomArea, GTK_PANZOOM_AREA,
Gtk::DrawingArea, GtkDrawingArea);
~~~
And here is the type declaration in `panzoomarea.h`:
~~~
G_DECLARE_DERIVABLE_TYPE(GtkPanZoomArea, gtk_panzoom_area, GTK,
PANZOOM_AREA,
GtkDrawingArea);
~~~
Does anyone know what I'm doing wrong here? The code for
`get_widget_checked` in `builder.ccg`[2] looks like it would print errors
if there were any problem retrieving the widget and checking the type and
since it does neither of these, it seems to be a problem in `Glib::wrap`.
For some reason `Glib::wrap` is constructing a C++ object other than my
object. It appears to be constructing a `Gtk::DrawingArea`. Assuming the
`Glib::wrap` uses the gobject type registry, I added the following in my
`main()`:
~~~
auto _ignoreme = Gtk::PanZoomArea::get_type();
(void)_ignoreme;
~~~
but this did not fix the problem.
[1]:
https://developer.gnome.org/gtkmm-tutorial/stable/chapter-wrapping-c-libraries.html.en
[2]: https://fossies.org/linux/gtkmm/gtk/src/builder.ccg#290
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