Detecting whether a widget is displayed.

[Daniel Burrows-4]

  Hi list,

  I have what's probably a simple GTK+ problem, and I was wondering if
anyone could give me a tip.

  I'm trying to write a custom widget (in GTK--) that would benefit
from knowing whether it's currently visible or not.  It seems pretty
easy to detect when a widget becomes visible for the first time by
hooking into the "expose" signal, but I can't for the life of me find
any way of detecting when a widget becomes invisible.  (for instance,
when the user switches away from its tab in a notebook or scrolls past
it in a TextView)

  The most promising thing I found was the "visibility notify event",
but it never seems to get delivered to my widget.  I've also tried to
use is_viewable() and get_visible_region() on the GDK window, but even
if these work (they don't seem to so far, but I could be doing it
wrong) I need a signal or event so that I know when to test them.

  Any suggestions?

    Thanks,
  Daniel
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[Lars Wirzenius-5]

On Thu, 2009-11-05 at 06:28 -0800, Daniel Burrows wrote:
>   I'm trying to write a custom widget (in GTK--) that would benefit
> from knowing whether it's currently visible or not.

Do the map-event and unmap-event signals on GtkWidget do what you need?


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[Daniel Burrows-4]

On Thu, Nov 05, 2009 at 04:31:27PM +0200, Lars Wirzenius <liw@...> was heard to say:
> On Thu, 2009-11-05 at 06:28 -0800, Daniel Burrows wrote:
> >   I'm trying to write a custom widget (in GTK--) that would benefit
> > from knowing whether it's currently visible or not.
>
> Do the map-event and unmap-event signals on GtkWidget do what you need?

  I tried them earlier -- it didn't seem like my object was ever
receiving the map or unmap events, though.  I can take another look;
maybe my test was wrong.

  One other thing that occurred to me since I wrote that first mail is
that maybe I need to wrap an event box around the image.  Do
map/unmap/visibility-notify events work on images at all?

  Daniel
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[Lars Wirzenius-5]

On Thu, 2009-11-05 at 07:58 -0800, Daniel Burrows wrote:

> On Thu, Nov 05, 2009 at 04:31:27PM +0200, Lars Wirzenius <liw@...> was heard to say:
> > On Thu, 2009-11-05 at 06:28 -0800, Daniel Burrows wrote:
> > >   I'm trying to write a custom widget (in GTK--) that would benefit
> > > from knowing whether it's currently visible or not.
> >
> > Do the map-event and unmap-event signals on GtkWidget do what you need?
>
>   I tried them earlier -- it didn't seem like my object was ever
> receiving the map or unmap events, though.  I can take another look;
> maybe my test was wrong.

Did you connect to map or map-event? Both signals seem to exist. I think
the latter is the one you'd want. (Ditto for unmap and unmap-event.)

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[Chris Vine]

On Thu, 5 Nov 2009 06:28:36 -0800
Daniel Burrows <dburrows@...> wrote:

>
>   I have what's probably a simple GTK+ problem, and I was wondering if
> anyone could give me a tip.
>
>   I'm trying to write a custom widget (in GTK--) that would benefit
> from knowing whether it's currently visible or not.  It seems pretty
> easy to detect when a widget becomes visible for the first time by
> hooking into the "expose" signal, but I can't for the life of me find
> any way of detecting when a widget becomes invisible.  (for instance,
> when the user switches away from its tab in a notebook or scrolls past
> it in a TextView)
>
>   The most promising thing I found was the "visibility notify event",
> but it never seems to get delivered to my widget.  I've also tried to
> use is_viewable() and get_visible_region() on the GDK window, but even
> if these work (they don't seem to so far, but I could be doing it
> wrong) I need a signal or event so that I know when to test them.

You need to add the GDK_VISIBILITY_NOTIFY_MASK for the widget with
gtk_widget_add_events() in order to get visibility notify events on it.
Also test GTK_WIDGET_VISIBLE() if you might call hide() on the widget
(eg when in the system tray), because hiding a widget for some reason
does not count as a change of visibility status.  Depending on what
you are after, you may also want to track window state events for cases
where a window is iconified (minimised).

In other words, a lot depends on what you mean by "visible".  Your
meaning many not be the same as GDK's meaning.  If you test for all of
the conditions I have mentioned it will probably do what you want.

Chris


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