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List:       gtk-app-devel
Subject:    Re: Arguments in GObject-based object constructor
From:       Roger Leigh <rleigh () whinlatter ! ukfsn ! org>
Date:       2005-05-30 22:18:32
Message-ID: 87wtpguzlz.fsf () hardknott ! home ! whinlatter ! ukfsn ! org
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Jacob Kroon <jacob.kroon@gmail.com> writes:

> Lets say I've written an abstract class Foo (a class that is not
> supposed to be instantiated), and a class that inherits from Foo
> called Bar, which is instantiable. Foo takes 2 constructor
> arguments/properties "x" and "y". Bar:s constructor takes the samt
> arguments. In order to initialize some of Bar:s attributes, it needs
> to know both "x" and "y". In the bar_init() function I can't get the
> "x" and "y" properties, because they arent set yet, so where do I
> initialize the attributes?

Object properties are set after construction has finished.  That is,
after the contructors and init functions have been called.  You need
to override the get_property and set_property vfuncs of GObjectClass,
and install properties of type G_PARAM_CONSTRUCT.

As an example, have a look at

http://arch.debian.org/cgi-bin/archzoom.cgi/rleigh@debian.org--2005-uterm/uterm--mainline--0.1--patch-41/cse/cse-selection.h?template=plain
 http://arch.debian.org/cgi-bin/archzoom.cgi/rleigh@debian.org--2005-uterm/uterm--mainline--0.1--patch-41/cse/cse-selection.c?template=plain


This is a type derived from GObject.  Here's an example for a type
derived from GtkWidget (hrm, just spotted a bug!):

http://arch.debian.org/cgi-bin/archzoom.cgi/rleigh@debian.org--2005-uterm/uterm--mainline--0.1--patch-41/cse/cse-canvas.h?template=plain
 http://arch.debian.org/cgi-bin/archzoom.cgi/rleigh@debian.org--2005-uterm/uterm--mainline--0.1--patch-41/cse/cse-canvas.c?template=plain


> Should I hook into the get/set property of both "x" and "y", and
> once both are set (check with some boolean variables), I can
> initialize them in bar_set_property() ?  That way sounds a little
> too complicated so I think I'm missing something.

If "x" and "y" are properties of the parent Bar class, simply call
g_object_new() with the properties to set.  You don't need to do
anything more, since it will handle setting the properties for you.


Regards,
Roger

- -- 
Roger Leigh
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