Re: signal_button_press_event() not sending signal?

[Antonio Coralles <noche suapie reflex at>]

Matthew Ryan Hurne wrote:

> On Sun, 2004-12-19 at 22:59 +0100, Antonio Coralles wrote:
> > Matthew Ryan Hurne wrote:
> >
> > > First of all, let me hint that I am very new to Gtkmm programming, and
> > > relatively new to C++ programming in general.
> > >
> > > I am trying to write a simple program that draws a bezier curve in a
> > > DrawingArea which can be manipulated by clicking and dragging its
> > > control points.
> > >
> > > Right now the program draws a curve, but I have not yet successfully
> > > implemented anything to manipulate it.  That's what I'm working on.
> > >
> > > I figured I'd start by figuring out how to detect a button click on the
> > > DrawingArea.  I know I'll need to get the coordinates of the mouse
> > > pointer as well.  From reading the tutorial, etc. it seemed that
> > > Widget::signal_button_press_event() is the appropriate method to 
> use.  I
> > > have connected it to a signal handler in my MainWindow class.
> > > Everything compiles fine but the code in my signal handler doesn't seem
> > > to execute.
> > >
> > > Here's what code it seems you'd need.
> > > In MainWindow's constructor (curveArea is my DrawingArea):
> > >
> > > curveArea.signal_button_press_event().connect(sigc::mem_fun(*this,
> > > &MainWindow::on_curve_button_press_event));
> > >
> > > A protected member of MainWindow:
> > >
> > > bool MainWindow::on_curve_button_press_event(GdkEventButton* event)
> > > {
> > >         std::cout << "The drawing area was clicked" << std::endl;
> > >
> > >         return true;
> > > }
> > >
> > > I searched the web for a while trying to find any hints, and was only
> > > able to find something on a mailing list from 2002 that said it was a
> > > bug.  Seems like that wouldn't be relevant anymore.  Any help would be
> > > greatly appreciated.  If you want all my source code, I can attach 
> it in
> > > a future e-mail.  I wasn't sure if that was proper mailing list
> > > etiquette so I figured I'd leave it out in this message.  Oh and one
> > > more thing...I'm having a lot of fun learning all this stuff.  :-)
> > >
> > > Matthew Hurne
> > >
> > > _______________________________________________
> > > gtkmm-list mailing list
> > > gtkmm-list gnome org <mailto:> <mailto:>
> > > http://mail.gnome.org/mailman/listinfo/gtkmm-list
> >
> > I would suggest you to read
> > http://www.gtkmm.org/docs/gtkmm-2.4/docs/tutorial/html/ch14.html. To
> > detect mouse clicks i would override bool
> > Gtk::Widget::on_button_press_event(GdkEventButton*  event)  ... For
> > further documentation for the various GdkEvent structs you may look at
> > http://developer.gnome.org/doc/API/2.0/gdk/gdk-Event-Structures.html.
> >
> > antonio
> > _______________________________________________
> > gtkmm-list mailing list
> > gtkmm-list gnome org <mailto:>
> > http://mail.gnome.org/mailman/listinfo/gtkmm-list
>
> Thanks for the tip on reading chapter 14, though I've already done that.
> I have been able to draw the curve, control points, and lines connected
> the control points just fine.  I haven't coded the interaction between
> the mouse and the curve, that's where I'm at now.
>
> Thanks a TON for the link to the GDK event structures.  Though right now
> I can't use it because it seems the mouse clicks aren't even being
> "detected", it will definitely be important when it comes to checking
> the mouse position and whether a control point has been clicked.
>
> I did what you suggested, or at least what I think you suggested, with
> no results.  I have inherited my own class, called CurveArea, from
> DrawingArea.  I overloaded its on_button_press_event(GdkEventButton
> *event) member with the following:
>
> bool CurveArea::on_button_press_event(GdkEventButton* event)
> {
>         if (event->type == GDK_BUTTON_PRESS && event->button == 1) {
>                std::cout << "The drawing area was clicked"
>                           << std::endl;
>         }
>
>         return true;
> }
>
> Here is the relevant line in CurveArea's constructor:
>
>         this->signal_button_press_event().connect(sigc::mem_fun(*this,
> &CurveArea::on_button_press_event));
>
> I'm guessing I don't need the this->, but I figured being explicit
> couldn't hurt.
Yes, you don't need it ....

> When clicking on the CurveArea, nothing is printed to the console.
> Help! Ahh!

Maybe you've put your drawing area into a widget which doesn't receive X 
events
[ http://www.gtkmm.org/docs/gtkmm-2.4/docs/tutorial/html/ch12.html ]. A 
Gtk::EventBox might help ...
By the way: are you working in windows or linux ?

> Oh, by the way, why does on_button_press_event have to return a bool?

To be honest, i'm not sure about this myself; as far as I know, 
returning true indicates that the event has been handled ....

antonio