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Ben Johnson <ben@xxxxxxxxx> writes:
> On Sat, Feb 19, 2005 at 11:47:15PM +0000, Roger Leigh wrote:
>> Ben Johnson <ben@xxxxxxxxx> writes:
>>
>> > I made a class that defines several _new() functions, which take various
>> > parameters. I now want to subclass from this and keep my various _new()
>> > functions with more or less the same parameters, and I want the behavior
>> > to stay the same too. I don't see anything in the documentation about
>> > how to do it though. anyone know?
>>
>> What about a factory function which allows one to choose the specific
>> derived type. For example,
>>
>> GtkGroupedToggle *
>> gtk_grouped_toggle_new_from_widget (GType group_toggle_type,
>> GtkGroupedToggle *group)
>> GtkGroupedToggle *new_toggle = NULL;
>>
>> g_return_val_if_fail(g_type_is_a(group_toggle_type,
>> GTK_TYPE_GROUPED_TOGGLE) == TRUE), NULL);
>>
>> new_toggle = g_object_new (type, NULL);
>> if( new_toggle )
>> new_toggle = gtk_grouped_toggle_add_to_list (new_toggle, group);
>>
>> return GTK_WIDGET(new_toggle);
>> }
>>
>> You now don't need any _new() functions for derived types.
>
> That's an interesting idea. So my objects of derived types would be
> created... like this?:
>
> w = gtk_grouped_toggle_new_from_widget (HPNT_TYPE_GROUPED_TOGGLE, NULL);
>
> huh. that's pretty cool. The base type doesn't need to know anything
> about derived types, but it supports them anyway and cuts down on
> coding. I might do that. (do I have it right? ...)
Yes, you've got it. (This is what the GnomeCanvas does, all derived
GnomeCanvasItems are created with gnome_canvas_item_new().
> #define HPNT_TYPE_GROUPED_TOGGLE (hpnt_grouped_toggle_get_type ())
>
>> Also, isn't it bad practice to have arguments to a _new() function
>> which are not construction parameters? Wouldn't it be better to add
>> to group manually, or have g_object_new in a method of the container
>> so it can't exist independently?
>
> I'm not sure what you mean by construction parameters.
Sorry, I meant construction /properties/ (properties created with
G_PARAM_CONSTRUCT), which are passed to g_object_new() for object
initialisation.
My understanding (which may be wrong) is that doing anything else in a
new() function (rather than in the object_init(), object_construct()
or with a construction parameter) makes is difficult to write language
bindings.
Regards,
Roger
- --
Roger Leigh
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