With the python exmaple, if I use Gtk.Window all is fine but with Hdy.Window, I have no round corner as promised. I have no decoration at all and the window can’t be moved.
The vala example uses Hdy.ApplicationWindow and the result is the same without changing anything in the code: no window decoration.
I use gtk-3.24 and libhandy-1.0.3. What am I doing wrong?
Both of those examples are outdated. The demo from my repo was written against 0.81.0 (an alpha version of 1.x, where we experimented with implicit init) and the Python example is from the repo itself and is perpetually outdated and in a need of rework. (the C demo is up to date)
You need to call Hdy.init() in Vala / Handy.init() in Python in:
If you have a GApplication, you do it in startup() after chaining up, e.g. like here
Otherwise after your gtk_init() call
In future we’ll probably have a GtkApplication subclass that does this automatically among other things.