java-gnome 4.0.2 (12 Feb 2007)
The End of the Beginning!
Major bugfixes and refactorings
Setting and getting properties on GObjects requires some tricky manoeuvring.
We implemented the code to do this early on, and it looked like our general
mechanism for getting Proxy instances for arbitrary pointers was working fine
for properties. It turns out, however, that when you call
g_type_name() on a
GValue containing a GObject, it returns the name of the type that was listed
when the property specification was registered, rather than saying it is a
GValue (as you might expect) or what the object actually is (that you might
also reasonably expect).
This led to all kinds of nastiness since the type name was what we were using
instanceFor() mechanism to discriminate (on the Java side) what kind
of Proxy subclass to create. The example we tripped over was asking for the
parent property of a Button packed into a VBox. What
g_type_name() told us
was “GtkContainer”, not “GtkVBox”! And that was a big problem, because
Container is abstract, and besides, we want to instantiate a concrete VBox
Proxy, not a Container one!
The solution basically boiled down to having two separate code paths: one
objectFor() [a greatly simplified version of the previous
instanceFor()] which returns normal Proxy objects for GObject subclasses
(Buttons and Labels and whatnot), and a new code path available via
valueFor() to specifically return our GValue Proxy for the cases where we
know we’re getting a GValue back. Since that occurs in limited and known
circumstances only (ie, when we’re getting properties) it’s no problem to know
which to use when.
Thanks to Davyd Madeley for extensive debugging assistance, and credit to Manish Singh, James Henstridge, and Malcolm Tredinnick for having analyzed the root cause issue and having clarified that two code paths would indeed be necessary.
As often happens when you kick a stone loose, we were able to do a number of refactorings to clean things up. This eventually led to the realization (ok, epiphany) that our treatment of the GValue mechanism was needlessly complex. Toss. We no longer have individual Value subclasses for each different fundamental type, but rather just leave them as opaque references.
This allowed a further simplification of the
valueFor() mechanism and even
more smashing about in Plumbing with a chainsaw. Net result was a reduction
by several hundred lines of code. Yeay!
All of these changes were confined to the internals of the binding machinery and are not user visible.
User interface designers are nothing new, but one of the really cool things
about GTK has long been the existence of
libglade. It’s a library which
takes the output of a one of the GNOME user interface designers (such as such
as Glade 3 or Gazpacho) and dynamically, at runtime, generates live
Windows full of Widgets!
With the arbitrary Proxy retrieval sorted out, the beginnings of a binding of
libglade was possible. None of the fancy stuff is there yet, but a
file can be loaded, and Widgets retrieved from the instantiated tree.
The JavaDoc for these classes clearly indicates that this is preliminary and subject to change. It may well all be blown away when GtkBuilder lands. We’ll see.
We’ve introduced the beginnings of a unit test framework. At the moment, this just evaluates various getters and setters without doing anything that requires the main loop. Despite this, the unit tests end up exercising the entire Proxy system discussed above; validating that the properties set and get and that the correct Proxy object is returned through a round trip is no mean feat.
You can run the suite from Eclipse, by specifying a JUnit 3 launcher on class
UnitTests in the default package in
tests/java, or by running
$ make test
the command line.
This release also sees the addition of
This is significant because GtkFileChooser is an interface in GTK, and
GtkFileChooserButton implements it. We’d been putting off the question of
dealing with GInterface (would it work or be a major problem?) for a while
now. We were delighted to find that the design implied by the re-engineered
bindings handled it cleanly, elegantly, and without any fuss. Another nice
validation of our new architecture.
Finally, a number of new signals were exposed on
though these were mostly the result of doing live demonstrations at
conferences of how easy extending the coverage of the new bindings is.
We have successfully implemented full GObject memory management in java-gnome 4.0 using GLib’s ToggleRef mechanism.
A strongly referenced Java Proxy will not allow its GObject to be destroyed out from underneath it; meanwhile, as long as the GObject is still referenced by something other than java-gnome, an otherwise only weakly reachable Java object that Proxies it will not be finalized. When the situation does occur whereby the GObject is only referenced from java-gnome, and the Java object is no longer strongly referenced by any other Java objects, then the Java object can be garbage collected and the GObject will be unref()’d and destroyed.
You can watch the reference system in action if you set
Huge thanks go to Vreixo Formoso Lopes who collaborated on the design, reviewed the implementation, and contributed test case code.
Build system improvements
A better detection of jni.h is done on Ubuntu, thanks to Michael Kedzierski. This makes java-gnome more likely to build out of the box on Debian-derived systems.
On the eve of release, Srichand Pendyala noticed that if you are running such
a system, a package named
libglade-dev needs to be installed. Of course, on
more modern systems all the necessary dependencies are present merely by
having GNOME installed in the first place. We’ll add a check for this Debian
specific behaviour in 4.0.3.
APIVERSION constants were moved to
so that anyone working on the Gtk main class isn’t forced to do a
re-configuration every time they save.
Installation and Packaging
java-gnome 4.0 now has the standard
make install command, and the equally
--prefix option to
$ ./configure --prefix=/usr $ make $ sudo make install
install target understands the
DESTDIR variable used by packagers to
install to a specified prefix within a temporary directory.
README file for details.
The feature additions described above were done to bring java-gnome up to
speed for the GTK & GNOME tutorial given at linux.conf.au. With that
past, we’re not going to do any more manual mockups of code in what will be
the generated layers. Focus now turns to designing and implementing the tool
that will parse
.defs files and output the translation code.
And so my firm returns to focusing on securing the funding needed to develop the project. Once more into the breach! When we succeed, the code generator will be our top priority and shouldn’t take more than a couple months to complete.
You can download java-gnome from
ftp.gnome.org or clone a branch from
mainline in our DVCS.