Re: connect_notify()

[Martin Schulze <martin-ml hippogriff de>]

Am 07.03.2005 11:35:55 schrieb(en) Matthias Kaeppler:
> Hello,
>
> I want a context menu to popup when the user right-clicks on a tree
> view. So I looked up signal_button_press_event() and I was told to
> either derive my own view from TreeView (I don't want that) and
> override
> the default handler, or use connect_notify() instead.
> Well, what does this mysterious function do? Googling for it turned
> out
> that it has something to do with coverting non-void return types to
> void
> return types of the signal handler (though I don't understand why  
> this
>
> is needed at all).
>
> Anyway, if I use this function to connect my own signal handler (as
> usual with sigc::mem_fun), the compiler complains about mismatching
> return types (the errors message is pretty long-winded, STL style,  
> you
>
> don't want to see it I guess...).
> Instead of posting the error message from g++, here's the code which
> caused it:
>
> // m_view is a TreeView
>
> m_view.signal_button_press_event().connect_notify( sigc::mem_fun(
> *this,
> &FileBrowser::on_rmb_clicked ) );
>
> // ...
>
> void FileBrowser::on_rmb_clicked()
> {
>     // ...
> }
>
> I don't get what's wrong here.

The function signature of your callback function does not match the  
function signature of the signal. It should look as follows:

void on_rmb_clicked(GdkEventButton* event)

for connect_notify() or

bool on_rmb_clicked(GdkEventButton* event)

for connect().

Like you already found out, the connect_notify() variant adds the  
boolean return value for you in such a way that the internal handling  
of an event is suppressed (which means a value of false, I think).

Regards,

 Martin


> --
> Matthias Kaeppler
>
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