Re: [java-gnome-hackers] HBox constructor causing segfaults.

[Tom B. <Tom...@Su...>]

Yeah, constructors can be evil, since a subclass can't control when its
superclass gets called.  What many toolkits do to work around this is to
define a protected "void init()" which gets called by the superclass's
constructor.  This allows a subclass like AppBar to do something like:

    public AppBar() {
        super();
        // initialization moved down...
    }

    protected init() {
        // initialization here
        super.init();
    }

The init method is a bit dangerous in that subclassers need to realize
that they are dealing with a partially-initialized object, but at least
their superclass can finish initialization with one that is.

An alternative I prefer is to have a protected constructor and a public
static factory method.  Constructors can then initialization objects
like they are supposed to, and the factory method can ensure that the
event handler hookup is called afterwards before a client is given the
object.  

The main drawback to using a static factory method is that it can't
support the Java Beans model, and so these components won't plug into a
form editor easily.

Tom

On Sat, 2002-10-19 at 21:18, Philip A. Chapman wrote:
> Everyone,
> 
> In the constructor org.gnu.gtk.HBox.HBox(), I commented out the line:
> 
> initializeEventHandlers();
> 
> The reason is that it causes segfaults when called during the
> construction of org.gnu.gnome.AppBar, which extends HBox.  AppBar works
> fine if I comment out the line in HBox as specified above and call
> initializeEventHandlers() from AppBar's constructor AFTER calling
> AppBar's gnome_appbar_new native method (thereby obtaining a handle).
> 
> The same applies for org.gnu.gnome.DateEdit as it also extends
> org.gnu.gtk.HBox.
> 
> Jeffrey,
> You are far more familiar with org_gnu_glib_GObject's create_callback
> method than I.  Would you mind looking into this?  Should subclasses of
> HBox simply always call initializeEventHandlers() or is there a way to
> make it work from HBox's constructor?
> 
> The good news is that the TestGNOME application pretty much works now. 
> There's a few annoying things, like buttons that do nothing on the
> dialogs that are opened from the main app.  However. there are no more
> segfaults and all the enabled buttons on the main app seem to be doing
> what they are supposed to.
> 
> Thanks,
> -- 
> Philip A. Chapman