Re: Custom container + Child type with interface

[David Nečas <yeti physics muni cz>]

On Sun, Dec 20, 2009 at 01:57:06PM +0000, Matthew Bucknall wrote:
> I'm implementing a custom container widget which needs to only accept
> child widgets which derive from GtkWidget (obviously) but also implement
> a custom Interface called GpanesPanel.
> 
> I'm not sure how to enforce this rule within my code's API. What type
> should the container's child_type() method return? GPANES_TYPE_PANEL or
> GTK_TYPE_WIDGET? Likewise, I'm not sure what type custom insertion
> methods for my container should accept, GpanesPanel or GtkWidget?
> 
> It doesn't seem enough to use GPANES_TYPE_PANEL/GpanesPanel because, as
> it stands, any non-widget class could implement the GpanesPanel
> interface but would be unusable as a container child.

Returing GPANES_TYPE_PANEL would be probably better as it can be ensured
that the thing is also a widget (see below).

Note that GtkContainer methods do not use child_type at preset,
gtk_container_add() simply checks that the child is a GtkWidget, leaving
specific checks for add() implementation in subclasses.  This might be
an implementation detail though...

> Is there anything I can put in the GpanesPanel interface definition that
> states that it can only be applied to classes derived from GtkWidget?

Yes, g_type_interface_add_prerequisite() can do that.

Yeti